Chakra B. Budhathoki; Thomas B. Lynch; James M. Guldin
2010-01-01
Nonlinear mixed-modeling methods were used to estimate parameters in an individual-tree basal area growth model for shortleaf pine (Pinus echinata Mill.). Shortleaf pine individual-tree growth data were available from over 200 permanently established 0.2-acre fixed-radius plots located in naturally-occurring even-aged shortleaf pine forests on the...
Individual-Tree Diameter Growth Models for Mixed Nothofagus Second Growth Forests in Southern Chile
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Paulo C. Moreno
2017-12-01
Full Text Available Second growth forests of Nothofagus obliqua (roble, N. alpina (raulí, and N. dombeyi (coihue, known locally as RORACO, are among the most important native mixed forests in Chile. To improve the sustainable management of these forests, managers need adequate information and models regarding not only existing forest conditions, but their future states with varying alternative silvicultural activities. In this study, an individual-tree diameter growth model was developed for the full geographical distribution of the RORACO forest type. This was achieved by fitting a complete model by comparing two variable selection procedures: cross-validation (CV, and least absolute shrinkage and selection operator (LASSO regression. A small set of predictors successfully explained a large portion of the annual increment in diameter at breast height (DBH growth, particularly variables associated with competition at both the tree- and stand-level. Goodness-of-fit statistics for this final model showed an empirical coefficient of correlation (R2emp of 0.56, relative root mean square error of 44.49% and relative bias of −1.96% for annual DBH growth predictions, and R2emp of 0.98 and 0.97 for DBH projection at 6 and 12 years, respectively. This model constitutes a simple and useful tool to support management plans for these forest ecosystems.
Directory of Open Access Journals (Sweden)
John A. KershawJr
2017-09-01
Full Text Available Background A novel approach to modelling individual tree growth dynamics is proposed. The approach combines multiple imputation and copula sampling to produce a stochastic individual tree growth and yield projection system. Methods The Nova Scotia, Canada permanent sample plot network is used as a case study to develop and test the modelling approach. Predictions from this model are compared to predictions from the Acadian variant of the Forest Vegetation Simulator, a widely used statistical individual tree growth and yield model. Results Diameter and height growth rates were predicted with error rates consistent with those produced using statistical models. Mortality and ingrowth error rates were higher than those observed for diameter and height, but also were within the bounds produced by traditional approaches for predicting these rates. Ingrowth species composition was very poorly predicted. The model was capable of reproducing a wide range of stand dynamic trajectories and in some cases reproduced trajectories that the statistical model was incapable of reproducing. Conclusions The model has potential to be used as a benchmarking tool for evaluating statistical and process models and may provide a mechanism to separate signal from noise and improve our ability to analyze and learn from large regional datasets that often have underlying flaws in sample design.
Stem analysis program (GOAP for evaluating of increment and growth data at individual tree
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Gafura Aylak Özdemir
2016-07-01
Full Text Available Stem analysis is a method evaluating in a detailed way data of increment and growth of individual tree at the past periods and widely used in various forestry disciplines. Untreated data of stem analysis consist of annual ring count and measurement procedures performed on cross sections taken from individual tree by section method. The evaluation of obtained this untreated data takes quite some time. Thus, a computer software was developed in this study to quickly and efficiently perform stem analysis. This computer software developed to evaluate untreated data of stem analysis as numerical and graphical was programmed as macro by utilizing Visual Basic for Application feature of MS Excel 2013 program currently the most widely used. In developed this computer software, growth height model is formed from two different approaches, individual tree volume depending on section method, cross-sectional area, increments of diameter, height and volume, volume increment percent and stem form factor at breast height are calculated depending on desired period lengths. This calculated values are given as table. Development of diameter, height, volume, increments of these variables, volume increment percent and stem form factor at breast height according to periodic age are given as chart. Stem model showing development of diameter, height and shape of individual tree in the past periods also can be taken from computer software as chart.
Effects of uncertainty in model predictions of individual tree volume on large area volume estimates
Ronald E. McRoberts; James A. Westfall
2014-01-01
Forest inventory estimates of tree volume for large areas are typically calculated by adding model predictions of volumes for individual trees. However, the uncertainty in the model predictions is generally ignored with the result that the precision of the large area volume estimates is overestimated. The primary study objective was to estimate the effects of model...
Dan Binkley; Jose Luiz Stape; William L. Bauerle; Michael G. Ryan
2010-01-01
The growth of wood in trees and forests depends on the acquisition of resources (light, water, and nutrients), the efficiency of using resources for photosynthesis, and subsequent partitioning to woody tissues. Patterns of efficiency over time for individual trees, or between trees at one time, result from changes in rates photosynthesis and shifts in...
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T. Sghaier
2013-12-01
Full Text Available Aim of study: The aim of the work was to develop an individual tree diameter-increment model for Thuya (Tetraclinis articulata in Tunisia.Area of study: The natural Tetraclinis articulata stands at Jbel Lattrech in north-eastern of Tunisia.Material and methods: Data came from 200 trees located in 50 sample plots. The diameter at age t and the diameter increment for the last five years obtained from cores taken at breast height were measured for each tree. Four difference equations derived from the base functions of Richards, Lundqvist, Hossfeld IV and Weibull were tested using the age-independent formulations of the growth functions. Both numerical and graphical analyses were used to evaluate the performance of the candidate models.Main results: Based on the analysis, the age-independent difference equation derived from the base function Richards model was selected. Two of the three parameters (growth rate and shape parameter of the retained model were related to site quality, represented by a Growth Index, stand density and the basal area in larger trees divided by diameter of the subject tree expressing the inter-tree competition.Research highlights: The proposed model can be useful for predicting the diameter growth of Tetraclinis articulata in Tunisia when age is not available or for trees growing in uneven-aged stands.Keywords: Age-independent growth model; difference equations; Tetraclinis articulata; Tunisia.
Liu, Tao; Im, Jungho; Quackenbush, Lindi J.
2015-12-01
This study provides a novel approach to individual tree crown delineation (ITCD) using airborne Light Detection and Ranging (LiDAR) data in dense natural forests using two main steps: crown boundary refinement based on a proposed Fishing Net Dragging (FiND) method, and segment merging based on boundary classification. FiND starts with approximate tree crown boundaries derived using a traditional watershed method with Gaussian filtering and refines these boundaries using an algorithm that mimics how a fisherman drags a fishing net. Random forest machine learning is then used to classify boundary segments into two classes: boundaries between trees and boundaries between branches that belong to a single tree. Three groups of LiDAR-derived features-two from the pseudo waveform generated along with crown boundaries and one from a canopy height model (CHM)-were used in the classification. The proposed ITCD approach was tested using LiDAR data collected over a mountainous region in the Adirondack Park, NY, USA. Overall accuracy of boundary classification was 82.4%. Features derived from the CHM were generally more important in the classification than the features extracted from the pseudo waveform. A comprehensive accuracy assessment scheme for ITCD was also introduced by considering both area of crown overlap and crown centroids. Accuracy assessment using this new scheme shows the proposed ITCD achieved 74% and 78% as overall accuracy, respectively, for deciduous and mixed forest.
Models to estimate volume of individual trees by morphometry of crowns obtained with lidar
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Evandro Orfanó Figueiredo
2014-12-01
Full Text Available The volumetric estimate from digital scanning of the forests through the use of LIDAR increases the precision of forest management techniques in planning tropical forest logging operations. The use of this remote detection technology allows the incorporation of crown morphometric variables which are still little known and little used due to the difficulty of collecting field data for volume equations. The objective of this study was to build equations capable of estimating the stem volume of dominant and codominant individual trees from the crown's morphometry obtained by airborne LIDAR, considering two forest inventory situations: a with the collection of diameter at breast height (DBH, and crown morphometric variables obtained from LIDAR data and b using only the crown morphometry variables. For the selection of models the factors considered were: the correlation matrix of predictor variables and the combination of variables that generates the best results by statistical criteria Syx, Syx(% and Pressp, and that were homoscedastic and had a normal and independent distribution of errors. The influence analysis was performed for the best equations. The results for the statistical fit of the equations to the two situations allowed the selection of models with and without DBH, with R2aj.( % values of a 92.92 and b 79.44, Syx(% values of a 16.73 and b 27.47, and, Pressp criterion values of a 201.15 m6 and b 537.47 m6, respectively. Through morphometric variables it was possible to develop equations capable of accurately estimating the stem volume of dominant and codominant trees in tropical forests.
Hao, Xu; Yujun, Sun; Xinjie, Wang; Jin, Wang; Yao, Fu
2015-01-01
A multiple linear model was developed for individual tree crown width of Cunninghamia lanceolata (Lamb.) Hook in Fujian province, southeast China. Data were obtained from 55 sample plots of pure China-fir plantation stands. An Ordinary Linear Least Squares (OLS) regression was used to establish the crown width model. To adjust for correlations between observations from the same sample plots, we developed one level linear mixed-effects (LME) models based on the multiple linear model, which take into account the random effects of plots. The best random effects combinations for the LME models were determined by the Akaike's information criterion, the Bayesian information criterion and the -2logarithm likelihood. Heteroscedasticity was reduced by three residual variance functions: the power function, the exponential function and the constant plus power function. The spatial correlation was modeled by three correlation structures: the first-order autoregressive structure [AR(1)], a combination of first-order autoregressive and moving average structures [ARMA(1,1)], and the compound symmetry structure (CS). Then, the LME model was compared to the multiple linear model using the absolute mean residual (AMR), the root mean square error (RMSE), and the adjusted coefficient of determination (adj-R2). For individual tree crown width models, the one level LME model showed the best performance. An independent dataset was used to test the performance of the models and to demonstrate the advantage of calibrating LME models.
A biologically-based individual tree model for managing the longleaf pine ecosystem
Rick Smith; Greg Somers
1998-01-01
Duration: 1995-present Objective: Develop a longleaf pine dynamics model and simulation system to define desirable ecosystem management practices in existing and future longleaf pine stands. Methods: Naturally-regenerated longleaf pine trees are being destructively sampled to measure their recent growth and dynamics. Soils and climate data will be combined with the...
T. Sghaier; M. Tome; J. Tome; M. Sanchez-Gonzalez; I. Cañellas; R. Calama
2013-01-01
Aim of study: The aim of the work was to develop an individual tree diameter-increment model for Thuya (Tetraclinis articulata) in Tunisia.Area of study: The natural Tetraclinis articulata stands at Jbel Lattrech in north-eastern of Tunisia.Material and methods: Data came from 200 trees located in 50 sample plots. The diameter at age t and the diameter increment for the last five years obtained from cores taken at breast height were measured for each tree. Four difference equations derived f...
Harvey A. Holt
1989-01-01
Controlling individual unwanted trees in forest stands is a readily accepted method for improving the value of future harvests. The practice is especially important in mixed hardwood forests where species differ considerably in value and within species individual trees differ in quality. Individual stem control is a mechanical or chemical weeding operation that...
Directory of Open Access Journals (Sweden)
R. J. L. Argamosa
2016-06-01
Full Text Available The generation of high resolution canopy height model (CHM from LiDAR makes it possible to delineate individual tree crown by means of a fully-automated method using the CHM’s curvature through its slope. The local maxima are obtained by taking the maximum raster value in a 3 m x 3 m cell. These values are assumed as tree tops and therefore considered as individual trees. Based on the assumptions, thiessen polygons were generated to serve as buffers for the canopy extent. The negative profile curvature is then measured from the slope of the CHM. The results show that the aggregated points from a negative profile curvature raster provide the most realistic crown shape. The absence of field data regarding tree crown dimensions require accurate visual assessment after the appended delineated tree crown polygon was superimposed to the hill shaded CHM.
Forest growth modeling in the Southern Region, National Forest System
International Nuclear Information System (INIS)
Belcher, D.M.
1988-01-01
This paper discusses an attempt to combine individual tree growth models and stand level growth models currently available for the Region into one computer program. Operation of the program is explained and growth models are included
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Aydın Kahriman
2012-11-01
Full Text Available The aim of this study is to investigate statistical relations between each of 12 competition indices (both distance-dependent and distance-independent and diameter growth of trees. Also we investigated the relations between each of 12 competition indices together with diameter at breast height and diameter growth. For that reason, six sampling plots (ranging from 1000 to 2000 m2 in size were taken from in mixed stands of Caucasion fir and Oriental spruce located within the Forest Management Districts of Torul and Artvin. Our results from those sampling plots were in agreement with general growth models. Regression analysis between each of competition indexes and diameter growth resulted in coefficients of determination (R2 values ranging from 30 to 64%. The distance-dependent competition indices gave stronger correlations with diameter growth than the distance-independent competition indexes. Coefficients of determination were even higher when competition indexes and dbh were used together as independent variables (R2 = 0.31 - 0.82.
Modelling diameter growth, mortality and recruitment of trees in ...
African Journals Online (AJOL)
Modelling diameter growth, mortality and recruitment of trees in miombo woodlands of Tanzania. ... Individual tree diameter growth and mortality models, and area-based recruitment models were developed. ... AJOL African Journals Online.
Growth models for Pinus patula in Angola | Delgado-Matas ...
African Journals Online (AJOL)
This study developed growth models for Pinus patula Schiede ex Schltdl. et Cham. for the Central Highlands of Angola for simulating the development of stand characteristics. The model set included dominant height, individual-tree diameter increment, individual-tree height and self-thinning models. The study was based ...
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Thelma Shirlen Soares
2004-12-01
Full Text Available Neste estudo foram conduzidos testes preliminares com o objetivo de avaliar um modelo de taper, proposto a partir da adaptação dos modelos desenvolvidos por Ormerod (1973 e Turnbull (1979, caracterizados pela sua simplicidade e facilidade de ajuste. Em comparação com modelos já consagrados, observou-se que o modelo alternativo apresentou consistência nos ajustes realizados. Portanto, pode-se concluir que o modelo apresentado é recomendável para a quantificação de multiprodutos de árvores individuais.Preliminary tests were conducted with the objective of evaluating a taper model, proposed from the adaptation of the models developed by Ormerod (1973 and Turnbull (1979, characterized by the simplicity and adjustment easiness. After adjustments and comparisons with other consecrated models, it was observed that the alternative model presented consistency in the carried out adjustments. In conclusion, the presented model can be recommended for multiproduct quantification of individual trees.
Jeremy W. Lichstein; Jonathan Dushoff; Kiona Ogle; Anping Chen; Drew W. Purves; John P. Caspersen; Stephen W. Pacala
2010-01-01
Geographically extensive forest inventories, such as the USDA Forest Service's Forest Inventory and Analysis (FIA) program, contain millions of individual tree growth and mortality records that could be used to develop broad-scale models of forest dynamics. A limitation of inventory data, however, is that individual-level measurements of light (L) and other...
Nakai, T.; Kumagai, T.; Saito, T.; Matsumoto, K.; Kume, T.; Nakagawa, M.; Sato, H.
2015-12-01
Bornean tropical rain forests are among the moistest biomes of the world with abundant rainfall throughout the year, and considered to be vulnerable to a change in the rainfall regime; e.g., high tree mortality was reported in such forests induced by a severe drought associated with the ENSO event in 1997-1998. In order to assess the effect (risk) of future climate change on eco-hydrology in such tropical rain forests, it is important to understand the water use of trees individually, because the vulnerability or mortality of trees against climate change can depend on the size of trees. Therefore, we refined the Spatially Explicit Individual-Based Dynamic Global Vegetation Model (SEIB-DGVM) so that the transpiration and its control by stomata are calculated for each individual tree. By using this model, we simulated the transpiration of each tree and its DBH-size dependency, and successfully reproduced the measured data of sap flow of trees and eddy covariance flux data obtained in a Bornean lowland tropical rain forest in Lambir Hills National Park, Sarawak, Malaysia.
Charles H. (Hobie) Perry; Kevin J. Horn; R. Quinn Thomas; Linda H. Pardo; Erica A.H. Smithwick; Doug Baldwin; Gregory B. Lawrence; Scott W. Bailey; Sabine Braun; Christopher M. Clark; Mark Fenn; Annika Nordin; Jennifer N. Phelan; Paul G. Schaberg; Sam St. Clair; Richard Warby; Shaun Watmough; Steven S. Perakis
2015-01-01
The abundance of temporally and spatially consistent Forest Inventory and Analysis data facilitates hierarchical/multilevel analysis to investigate factors affecting tree growth, scaling from plot-level to continental scales. Herein we use FIA tree and soil inventories in conjunction with various spatial climate and soils data to estimate species-specific responses of...
Monitoring individual tree-based change with airborne lidar.
Duncanson, Laura; Dubayah, Ralph
2018-05-01
Understanding the carbon flux of forests is critical for constraining the global carbon cycle and managing forests to mitigate climate change. Monitoring forest growth and mortality rates is critical to this effort, but has been limited in the past, with estimates relying primarily on field surveys. Advances in remote sensing enable the potential to monitor tree growth and mortality across landscapes. This work presents an approach to measure tree growth and loss using multidate lidar campaigns in a high-biomass forest in California, USA. Individual tree crowns were delineated in 2008 and again in 2013 using a 3D crown segmentation algorithm, with derived heights and crown radii extracted and used to estimate individual tree aboveground biomass. Tree growth, loss, and aboveground biomass were analyzed with respect to tree height and crown radius. Both tree growth and loss rates decrease with increasing tree height, following the expectation that trees slow in growth rate as they age. Additionally, our aboveground biomass analysis suggests that, while the system is a net source of aboveground carbon, these carbon dynamics are governed by size class with the largest sources coming from the loss of a relatively small number of large individuals. This study demonstrates that monitoring individual tree-based growth and loss can be conducted with multidate airborne lidar, but these methods remain relatively immature. Disparities between lidar acquisitions were particularly difficult to overcome and decreased the sample of trees analyzed for growth rate in this study to 21% of the full number of delineated crowns. However, this study illuminates the potential of airborne remote sensing for ecologically meaningful forest monitoring at an individual tree level. As methods continue to improve, airborne multidate lidar will enable a richer understanding of the drivers of tree growth, loss, and aboveground carbon flux.
Individual tree diameter, height, and volume functions for longleaf pine
Carlos A. Gonzalez-Benecke; Salvador A. Gezan; Timothy A. Martin; Wendell P. Cropper; Lisa J. Samuelson; Daniel J. Leduc
2014-01-01
Currently, little information is available to estimate individual tree attributes for longleaf pine (Pinus palustris Mill.), an important tree species of the southeastern United States. The majority of available models are local, relying on stem diameter outside bark at breast height (dbh, cm) and not including stand-level parameters. We developed...
Evan Johnson; Michael Kane; Dehai Zhao; Robert Teskey
2015-01-01
Three existing loblolly pine (Pinus taeda L.) installations in the Plantation Management Research Cooperative's Upper Coastal Plain/Piedmont Culture Density Study were used to examine the effects of two cultural intensities, four initial planting densities, and their interactions on stem growth at the individual tree level from age 12 to 15 years and at the stand...
Visualizing Individual Tree Differences in Tree-Ring Studies
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Mario Trouillier
2018-04-01
Full Text Available Averaging tree-ring measurements from multiple individuals is one of the most common procedures in dendrochronology. It serves to filter out noise from individual differences between trees, such as competition, height, and micro-site effects, which ideally results in a site chronology sensitive to regional scale factors such as climate. However, the climate sensitivity of individual trees can be modulated by factors like competition, height, and nitrogen deposition, calling attention to whether average chronologies adequately assess climatic growth-control. In this study, we demonstrate four simple but effective methods to visually assess differences between individual trees. Using individual tree climate-correlations we: (1 employed jitter plots with superimposed metadata to assess potential causes for these differences; (2 plotted the frequency distributions of climate correlations over time as heat maps; (3 mapped the spatial distribution of climate sensitivity over time to assess spatio-temporal dynamics; and (4 used t-distributed Stochastic Neighborhood Embedding (t-SNE to assess which trees were generally more similar in terms of their tree-ring pattern and their correlation with climate variables. This suite of exploratory methods can indicate if individuals in tree-ring datasets respond differently to climate variability, and therefore, should not solely be explored with climate correlations of the mean population chronology.
Ralph L. Amateis; Harold E. Burkhart
2016-01-01
Site index is the most common metric of site productivity in loblolly pine plantations. GenerallyÂ applied as a constant for a particular stand, it provides an overall measure of a siteâs ability to grow trees.Â It is well known, however, that even the most uniform stands can have considerable variation in site indexÂ due to soil factors that influence microsite,...
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Dan A. MacIsaac
2011-09-01
Full Text Available We investigated the relationship of stem diameter to tree, site and stand characteristics for six major tree species (trembling aspen, white birch, balsam fir, lodgepole pine, black spruce, and white spruce in Alberta (Canada with data from Alberta Sustainable Resource Development Permanent Sample Plots. Using non-linear mixed effects modeling techniques, we developed models to estimate diameter at breast height using height, crown and stand attributes. Mixed effects models (with plot as subject using height, crown area, and basal area of the larger trees explained on average 95% of the variation in diameter at breast height across the six species with a root mean square error of 2.0 cm (13.4% of mean diameter. Fixed effects models (without plot as subject including the Natural Sub-Region (NSR information explained on average 90% of the variation in diameter at breast height across the six species with a root mean square error equal to 2.8 cm (17.9% of mean diameter. Selected climate variables provided similar results to models with NSR information. The inclusion of nutrient regime and moisture regime did not significantly improve the predictive ability of these models.
Adjusting the Stems Regional Forest Growth Model to Improve Local Predictions
W. Brad Smith
1983-01-01
A simple procedure using double sampling is described for adjusting growth in the STEMS regional forest growth model to compensate for subregional variations. Predictive accuracy of the STEMS model (a distance-independent, individual tree growth model for Lake States forests) was improved by using this procedure
Ambros Berger; Thomas Gschwantner; Ronald E. McRoberts; Klemens. Schadauer
2014-01-01
National forest inventories typically estimate individual tree volumes using models that rely on measurements of predictor variables such as tree height and diameter, both of which are subject to measurement error. The aim of this study was to quantify the impacts of these measurement errors on the uncertainty of the model-based tree stem volume estimates. The impacts...
Berger, U.; Hildenbrandt, H.
2003-01-01
We simulated the self-thinning of Rhizophora mangle mangrove forests with the spatially explicit simulation model KiWi. This model is an application of the field-of-neighbourhood (FON) approach, which describes an individual tree by a competition function defined on the zone of influence (ZOI)
Pradip Saud; Thomas B. Lynch; Duncan S. Wilson; John Stewart; James M. Guldin; Bob Heinemann; Randy Holeman; Dennis Wilson; Keith Anderson
2015-01-01
An individual-tree basal area growth model previously developed for even-aged naturally occurring shortleaf pine trees (Pinus echinata Mill.) in western Arkansas and southeastern Oklahoma did not include weather variables. Individual-tree growth and yield modeling of shortleaf pine has been carried out using the remeasurements of over 200 plots...
ACCURACY ASSESSMENT OF CROWN DELINEATION METHODS FOR THE INDIVIDUAL TREES USING LIDAR DATA
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K. T. Chang
2016-06-01
Full Text Available Forest canopy density and height are used as variables in a number of environmental applications, including the estimation of biomass, forest extent and condition, and biodiversity. The airborne Light Detection and Ranging (LiDAR is very useful to estimate forest canopy parameters according to the generated canopy height models (CHMs. The purpose of this work is to introduce an algorithm to delineate crown parameters, e.g. tree height and crown radii based on the generated rasterized CHMs. And accuracy assessment for the extraction of volumetric parameters of a single tree is also performed via manual measurement using corresponding aerial photo pairs. A LiDAR dataset of a golf course acquired by Leica ALS70-HP is used in this study. Two algorithms, i.e. a traditional one with the subtraction of a digital elevation model (DEM from a digital surface model (DSM, and a pit-free approach are conducted to generate the CHMs firstly. Then two algorithms, a multilevel morphological active-contour (MMAC and a variable window filter (VWF, are implemented and used in this study for individual tree delineation. Finally, experimental results of two automatic estimation methods for individual trees can be evaluated with manually measured stand-level parameters, i.e. tree height and crown diameter. The resulting CHM generated by a simple subtraction is full of empty pixels (called "pits" that will give vital impact on subsequent analysis for individual tree delineation. The experimental results indicated that if more individual trees can be extracted, tree crown shape will became more completely in the CHM data after the pit-free process.
Energy Technology Data Exchange (ETDEWEB)
Mielke, D. L.; Shugart, H. H.; West, D. C.
1977-04-01
This report is a user's manual for FORAR, a computer model simulating stand growth and composition of upland forests of south central Arkansas. The model computes: the number and biomass of each tree species, and the dbh, age, and species of each individual tree on a 1/12-ha circular plot.
Directory of Open Access Journals (Sweden)
Maggi Kelly
2013-08-01
Full Text Available Light detection and ranging (lidar data is increasingly being used for ecosystem monitoring across geographic scales. This work concentrates on delineating individual trees in topographically-complex, mixed conifer forest across the California’s Sierra Nevada. We delineated individual trees using vector data and a 3D lidar point cloud segmentation algorithm, and using raster data with an object-based image analysis (OBIA of a canopy height model (CHM. The two approaches are compared to each other and to ground reference data. We used high density (9 pulses/m2, discreet lidar data and WorldView-2 imagery to delineate individual trees, and to classify them by species or species types. We also identified a new method to correct artifacts in a high-resolution CHM. Our main focus was to determine the difference between the two types of approaches and to identify the one that produces more realistic results. We compared the delineations via tree detection, tree heights, and the shape of the generated polygons. The tree height agreement was high between the two approaches and the ground data (r2: 0.93–0.96. Tree detection rates increased for more dominant trees (8–100 percent. The two approaches delineated tree boundaries that differed in shape: the lidar-approach produced fewer, more complex, and larger polygons that more closely resembled real forest structure.
Assessing Precision in Conventional Field Measurements of Individual Tree Attributes
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Ville Luoma
2017-02-01
Full Text Available Forest resource information has a hierarchical structure: individual tree attributes are summed at the plot level and then in turn, plot-level estimates are used to derive stand or large-area estimates of forest resources. Due to this hierarchy, it is imperative that individual tree attributes are measured with accuracy and precision. With the widespread use of different measurement tools, it is also important to understand the expected degree of precision associated with these measurements. The most prevalent tree attributes measured in the field are tree species, stem diameter-at-breast-height (dbh, and tree height. For dbh and height, the most commonly used measuring devices are calipers and clinometers, respectively. The aim of our study was to characterize the precision of individual tree dbh and height measurements in boreal forest conditions when using calipers and clinometers. The data consisted of 319 sample trees at a study area in Evo, southern Finland. The sample trees were measured independently by four trained mensurationists. The standard deviation in tree dbh and height measurements was 0.3 cm (1.5% and 0.5 m (2.9%, respectively. Precision was also assessed by tree species and tree size classes; however, there were no statistically significant differences between the mensurationists for dbh or height measurements. Our study offers insights into the expected precision of tree dbh and height as measured with the most commonly used devices. These results are important when using sample plot data in forest inventory applications, especially now, at a time when new tree attribute measurement techniques based on remote sensing are being developed and compared to the conventional caliper and clinometer measurements.
James A. Moore; David A Hamilton; Yu Xiao; John Byrne
2004-01-01
Individual tree mortality models for western white pine (Pinus monticola Dougl. ex D. Don), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), western redcedar (Thuja plicata Donn ex. D. Don), western hemlock (Tsuga heterophylla (Raf.) Sarg.), and western larch (Larix occidentalis Nutt.) were developed using data...
Non-Destructive, Laser-Based Individual Tree Aboveground Biomass Estimation in a Tropical Rainforest
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Muhammad Zulkarnain Abd Rahman
2017-03-01
Full Text Available Recent methods for detailed and accurate biomass and carbon stock estimation of forests have been driven by advances in remote sensing technology. The conventional approach to biomass estimation heavily relies on the tree species and site-specific allometric equations, which are based on destructive methods. This paper introduces a non-destructive, laser-based approach (terrestrial laser scanner for individual tree aboveground biomass estimation in the Royal Belum forest reserve, Perak, Malaysia. The study area is in the state park, and it is believed to be one of the oldest rainforests in the world. The point clouds generated for 35 forest plots, using the terrestrial laser scanner, were geo-rectified and cleaned to produce separate point clouds for individual trees. The volumes of tree trunks were estimated based on a cylinder model fitted to the point clouds. The biomasses of tree trunks were calculated by multiplying the volume and the species wood density. The biomasses of branches and leaves were also estimated based on the estimated volume and density values. Branch and leaf volumes were estimated based on the fitted point clouds using an alpha-shape approach. The estimated individual biomass and the total above ground biomass were compared with the aboveground biomass (AGB value estimated using existing allometric equations and individual tree census data collected in the field. The results show that the combination of a simple single-tree stem reconstruction and wood density can be used to estimate stem biomass comparable to the results usually obtained through existing allometric equations. However, there are several issues associated with the data and method used for branch and leaf biomass estimations, which need further improvement.
E. Gregory McPherson; Paula J. Peper
2012-01-01
This paper describes three long-term tree growth studies conducted to evaluate tree performance because repeated measurements of the same trees produce critical data for growth model calibration and validation. Several empirical and process-based approaches to modeling tree growth are reviewed. Modeling is more advanced in the fields of forestry and...
An individual-based growth and competition model for coastal redwood forest restoration
van Mantgem, Phillip J.; Das, Adrian J.
2014-01-01
Thinning treatments to accelerate coastal redwood forest stand development are in wide application, but managers have yet to identify prescriptions that might best promote Sequoia sempervirens (Lamb. ex D. Don) Endl. (redwood) growth. The creation of successful thinning prescriptions would be aided by identifying the underlying mechanisms governing how individual tree growth responds to competitive environments in coastal redwood forests. We created a spatially explicit individual-based model of tree competition and growth parameterized using surveys of upland redwood forests at Redwood National Park, California. We modeled competition for overstory trees (stems ≥ 20 cm stem diameter at breast height, 1.37 m (dbh)) as growth reductions arising from sizes, distances, and species identity of competitor trees. Our model explained up to half of the variation in individual tree growth, suggesting that neighborhood crowding is an important determinant of growth in this forest type. We used our model to simulate the effects of novel thinning prescriptions (e.g., 40% stand basal area removal) for redwood forest restoration, concluding that these treatments could lead to substantial growth releases, particularly for S. sempervirens. The results of this study, along with continued improvements to our model, will help to determine spacing and species composition that best encourage growth.
A novel approach for individual tree crown delineation using lidar data
Liu, Tao
Individual tree crown delineation (ITCD) is an important technique to support precision forestry. ITCD is particularly difficult for deciduous forests where the existence of multiple branches can lead to false tree top detection. This thesis focused on developing a new ITCD model, which consists of two components: (1) boundary refinement using a novel algorithm called Fishing Net Dragging (FiND), and (2) segment merging using boundary classification. The proposed ITCD model was tested in both deciduous and mixed forests, attaining an overall accuracy of 74% and 78%, respectively. This compared favorably to an ITCD method commonly cited in the literature, which attained 41% and 51% on the same plots. To facilitate comparison of research in the ITCD community, this thesis also developed a new accuracy assessment scheme for ITCD. This new accuracy assessment is easy to interpret and convenient to implement while comprehensively evaluating ITCD accuracy.
Liu, Feng; Tan, Chang; Lei, Pi-Feng
2014-11-01
Taking Wugang forest farm in Xuefeng Mountain as the research object, using the airborne light detection and ranging (LiDAR) data under leaf-on condition and field data of concomitant plots, this paper assessed the ability of using LiDAR technology to estimate aboveground biomass of the mid-subtropical forest. A semi-automated individual tree LiDAR cloud point segmentation was obtained by using condition random fields and optimization methods. Spatial structure, waveform characteristics and topography were calculated as LiDAR metrics from the segmented objects. Then statistical models between aboveground biomass from field data and these LiDAR metrics were built. The individual tree recognition rates were 93%, 86% and 60% for coniferous, broadleaf and mixed forests, respectively. The adjusted coefficients of determination (R(2)adj) and the root mean squared errors (RMSE) for the three types of forest were 0.83, 0.81 and 0.74, and 28.22, 29.79 and 32.31 t · hm(-2), respectively. The estimation capability of model based on canopy geometric volume, tree percentile height, slope and waveform characteristics was much better than that of traditional regression model based on tree height. Therefore, LiDAR metrics from individual tree could facilitate better performance in biomass estimation.
Metzger, Johanna Clara; Germer, Sonja; Hildebrandt, Anke
2017-04-01
The redistribution of precipitation by canopies changes the water flow dynamics to the forest floor. The spatial pattern of throughfall has been researched in a number of studies in different ecosystems. Yet, also stemflow substantially influences water input patterns, constituting a mean of 12% of gross precipitation for European beech as one of the most abundant tree species in Central Europe. While the initiation of stemflow depends mostly on precipitation event properties, stemflow amounts are strongly shaped by canopy structure. Stemflow research has mainly addressed the impact of single tree morphological variables. In previous studies, the impact of forest structure on area-based stemflow was studied comparing plots with different properties using few exemplary stemflow measurements. In non-homogeneous stands, this approach might not be accurate, as the variation of stand properties like tree density could change tree individual stemflow fluxes. To investigate this, a total measurement of all trees per plot is required. We hypothesize, that in addition to individual tree metrics, tree neighborhood relations have a significant impact on stemflow generation in a heterogeneous beech forest. Our study site is located in the pristine forest of the National Park Hainich, central Germany. It is heterogeneous in respect to tree density, species composition and tree age. We measured stemflow in an areal approach, for all trees on 11 subplots (each 10 m x 10 m) spaced evenly throughout a 1 ha plot. This involved overall 65 trees, which is 11% of the plot's trees. 27 precipitation events were recorded in spring and early summer of 2015 and 2016. Stand properties were surveyed, including diameter at breast height, height, position and species of a tree. From this data, we calculated neighborhood properties for each tree, as number, basal area, and relative height of neighboring trees within a radius of the plot's mean tree distance. Using linear mixed effects models, we
A Novel Modelling Approach for Predicting Forest Growth and Yield under Climate Change.
Directory of Open Access Journals (Sweden)
M Irfan Ashraf
Full Text Available Global climate is changing due to increasing anthropogenic emissions of greenhouse gases. Forest managers need growth and yield models that can be used to predict future forest dynamics during the transition period of present-day forests under a changing climatic regime. In this study, we developed a forest growth and yield model that can be used to predict individual-tree growth under current and projected future climatic conditions. The model was constructed by integrating historical tree growth records with predictions from an ecological process-based model using neural networks. The new model predicts basal area (BA and volume growth for individual trees in pure or mixed species forests. For model development, tree-growth data under current climatic conditions were obtained using over 3000 permanent sample plots from the Province of Nova Scotia, Canada. Data to reflect tree growth under a changing climatic regime were projected with JABOWA-3 (an ecological process-based model. Model validation with designated data produced model efficiencies of 0.82 and 0.89 in predicting individual-tree BA and volume growth. Model efficiency is a relative index of model performance, where 1 indicates an ideal fit, while values lower than zero means the predictions are no better than the average of the observations. Overall mean prediction error (BIAS of basal area and volume growth predictions was nominal (i.e., for BA: -0.0177 cm(2 5-year(-1 and volume: 0.0008 m(3 5-year(-1. Model variability described by root mean squared error (RMSE in basal area prediction was 40.53 cm(2 5-year(-1 and 0.0393 m(3 5-year(-1 in volume prediction. The new modelling approach has potential to reduce uncertainties in growth and yield predictions under different climate change scenarios. This novel approach provides an avenue for forest managers to generate required information for the management of forests in transitional periods of climate change. Artificial intelligence
Stochastic ontogenetic growth model
West, B. J.; West, D.
2012-02-01
An ontogenetic growth model (OGM) for a thermodynamically closed system is generalized to satisfy both the first and second law of thermodynamics. The hypothesized stochastic ontogenetic growth model (SOGM) is shown to entail the interspecies allometry relation by explicitly averaging the basal metabolic rate and the total body mass over the steady-state probability density for the total body mass (TBM). This is the first derivation of the interspecies metabolic allometric relation from a dynamical model and the asymptotic steady-state distribution of the TBM is fit to data and shown to be inverse power law.
International Nuclear Information System (INIS)
Waterman, T.E.; Takata, A.N.
1983-01-01
The IITRI Urban Fire Spread Model as well as others of similar vintage were constrained by computer size and running costs such that many approximations/generalizations were introduced to reduce program complexity and data storage requirements. Simplifications were introduced both in input data and in fire growth and spread calculations. Modern computational capabilities offer the means to introduce greater detail and to examine its practical significance on urban fire predictions. Selected portions of the model are described as presently configured, and potential modifications are discussed. A single tract model is hypothesized which permits the importance of various model details to be assessed, and, other model applications are identified
INDIVIDUAL TREE OF URBAN FOREST EXTRACTION FROM VERY HIGH DENSITY LIDAR DATA
Directory of Open Access Journals (Sweden)
A. Moradi
2016-06-01
Full Text Available Airborne LiDAR (Light Detection and Ranging data have a high potential to provide 3D information from trees. Most proposed methods to extract individual trees detect points of tree top or bottom firstly and then using them as starting points in a segmentation algorithm. Hence, in these methods, the number and the locations of detected peak points heavily effect on the process of detecting individual trees. In this study, a new method is presented to extract individual tree segments using LiDAR points with 10cm point density. In this method, a two-step strategy is performed for the extraction of individual tree LiDAR points: finding deterministic segments of individual trees points and allocation of other LiDAR points based on these segments. This research is performed on two study areas in Zeebrugge, Bruges, Belgium (51.33° N, 3.20° E. The accuracy assessment of this method showed that it could correctly classified 74.51% of trees with 21.57% and 3.92% under- and over-segmentation errors respectively.
Economic Growth Models Transition
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Coralia Angelescu
2006-03-01
Full Text Available The transitional recession in countries of Eastern Europe has been much longer than expected. The legacy and recent policy mistakes have both contributed to the slow progress. As structural reforms and gradual institution building have taken hold, the post-socialist economics have started to recover, with some leading countries building momentum toward faster growth. There is a possibility that in wider context of globalization several of these emerging market economies will be able to catch up with the more advanced industrial economies in a matter of one or two generations. Over the past few years, most candidate countries have made progress in the transition to a competitive market economy, macroeconomic stabilization and structural reform. However their income levels have remained far below those in the Member States. Measured by per capita income in purchasing power standards, there has been a very limited amount of catching up over the past fourteen years. Prior, the distinctions between Solow-Swan model and endogenous growth model. The interdependence between transition and integration are stated in this study. Finally, some measures of macroeconomic policy for sustainable growth are proposed in correlation with real macroeconomic situation of the Romanian economy. Our study would be considered the real convergence for the Romanian economy and the recommendations for the adequate policies to achieve a fast real convergence and sustainable growth.
Economic Growth Models Transition
Directory of Open Access Journals (Sweden)
Coralia Angelescu
2006-01-01
Full Text Available The transitional recession in countries of Eastern Europe has been much longer than expected. The legacy and recent policy mistakes have both contributed to the slow progress. As structural reforms and gradual institution building have taken hold, the post-socialist economics have started to recover, with some leading countries building momentum toward faster growth. There is a possibility that in wider context of globalization several of these emerging market economies will be able to catch up with the more advanced industrial economies in a matter of one or two generations. Over the past few years, most candidate countries have made progress in the transition to a competitive market economy, macroeconomic stabilization and structural reform. However their income levels have remained far below those in the Member States. Measured by per capita income in purchasing power standards, there has been a very limited amount of catching up over the past fourteen years. Prior, the distinctions between Solow-Swan model and endogenous growth model. The interdependence between transition and integration are stated in this study. Finally, some measures of macroeconomic policy for sustainable growth are proposed in correlation with real macroeconomic situation of the Romanian economy. Our study would be considered the real convergence for the Romanian economy and the recommendations for the adequate policies to achieve a fast real convergence and sustainable growth.
Individual tree detection based on densities of high points of high resolution airborne lidar
Abd Rahman, M.Z.; Gorte, B.G.H.
2008-01-01
The retrieval of individual tree location from Airborne LiDAR has focused largely on utilizing canopy height. However, high resolution Airborne LiDAR offers another source of information for tree detection. This paper presents a new method for tree detection based on high points’ densities from a
Logging damage using an individual tree selection practice in Appalachian hardwood stands
Neil I. Lamson; H. Clay Smith; Gary W. Miller
1985-01-01
Four West Virginia hardwood stands, managed using individual-tree selection for the past 30 years, were examined after the third and, in one instance, the fourth periodic harvest to determine the severity of logging damage. On existing skid roads, trees were removed with a rubber-tired skidder or a crawler tractor with a rubber-tired arch. Logging damage reduced...
Daniel A. Yaussy
2000-01-01
Two individual-tree growth simulators are used to predict the growth and mortality on a 30-year-old forest site and an 80-year-old forest site in eastern Kentucky. The empirical growth and yield model (NE-TWIGS) was developed to simulate short-term (
Wang, Le
2003-10-01
Modern forest management poses an increasing need for detailed knowledge of forest information at different spatial scales. At the forest level, the information for tree species assemblage is desired whereas at or below the stand level, individual tree related information is preferred. Remote Sensing provides an effective tool to extract the above information at multiple spatial scales in the continuous time domain. To date, the increasing volume and readily availability of high-spatial-resolution data have lead to a much wider application of remotely sensed products. Nevertheless, to make effective use of the improving spatial resolution, conventional pixel-based classification methods are far from satisfactory. Correspondingly, developing object-based methods becomes a central challenge for researchers in the field of Remote Sensing. This thesis focuses on the development of methods for accurate individual tree identification and tree species classification. We develop a method in which individual tree crown boundaries and treetop locations are derived under a unified framework. We apply a two-stage approach with edge detection followed by marker-controlled watershed segmentation. Treetops are modeled from radiometry and geometry aspects. Specifically, treetops are assumed to be represented by local radiation maxima and to be located near the center of the tree-crown. As a result, a marker image was created from the derived treetop to guide a watershed segmentation to further differentiate overlapping trees and to produce a segmented image comprised of individual tree crowns. The image segmentation method developed achieves a promising result for a 256 x 256 CASI image. Then further effort is made to extend our methods to the multiscales which are constructed from a wavelet decomposition. A scale consistency and geometric consistency are designed to examine the gradients along the scale-space for the purpose of separating true crown boundary from unwanted
Santos, E. G.; Jorge, A.; Shimabukuro, Y. E.; Gasparini, K.
2017-12-01
The State of Mato Grosso - MT has the second largest area with degraded forest among the states of the Brazilian Legal Amazon. Land use and land cover change processes that occur in this region cause the loss of forest biomass, releasing greenhouse gases that contribute to the increase of temperature on earth. These degraded forest areas lose biomass according to the intensity and magnitude of the degradation type. The estimate of forest biomass, commonly performed by forest inventory through sample plots, shows high variance in degraded forest areas. Due to this variance and complexity of tropical forests, the aim of this work was to estimate forest biomass using LiDAR point clouds in three distinct forest areas: one degraded by fire, another by selective logging and one area of intact forest. The approach applied in these areas was the Individual Tree Detection (ITD). To isolate the trees, we generated Canopy Height Models (CHM) images, which are obtained by subtracting the Digital Elevation Model (MDE) and the Digital Terrain Model (MDT), created by the cloud of LiDAR points. The trees in the CHM images are isolated by an algorithm provided by the Quantitative Ecology research group at the School of Forestry at Northern Arizona University (SILVA, 2015). With these points, metrics were calculated for some areas, which were used in the model of biomass estimation. The methodology used in this work was expected to reduce the error in biomass estimate in the study area. The cloud points of the most representative trees were analyzed, and thus field data was correlated with the individual trees found by the proposed algorithm. In a pilot study, the proposed methodology was applied generating the individual tree metrics: total height and area of the crown. When correlating 339 isolated trees, an unsatisfactory R² was obtained, as heights found by the algorithm were lower than those obtained in the field, with an average difference of 2.43 m. This shows that the
Comparing Individual Tree Segmentation Based on High Resolution Multispectral Image and Lidar Data
Xiao, P.; Kelly, M.; Guo, Q.
2014-12-01
This study compares the use of high-resolution multispectral WorldView images and high density Lidar data for individual tree segmentation. The application focuses on coniferous and deciduous forests in the Sierra Nevada Mountains. The tree objects are obtained in two ways: a hybrid region-merging segmentation method with multispectral images, and a top-down and bottom-up region-growing method with Lidar data. The hybrid region-merging method is used to segment individual tree from multispectral images. It integrates the advantages of global-oriented and local-oriented region-merging strategies into a unified framework. The globally most-similar pair of regions is used to determine the starting point of a growing region. The merging iterations are constrained within the local vicinity, thus the segmentation is accelerated and can reflect the local context. The top-down region-growing method is adopted in coniferous forest to delineate individual tree from Lidar data. It exploits the spacing between the tops of trees to identify and group points into a single tree based on simple rules of proximity and likely tree shape. The bottom-up region-growing method based on the intensity and 3D structure of Lidar data is applied in deciduous forest. It segments tree trunks based on the intensity and topological relationships of the points, and then allocate other points to exact tree crowns according to distance. The accuracies for each method are evaluated with field survey data in several test sites, covering dense and sparse canopy. Three types of segmentation results are produced: true positive represents a correctly segmented individual tree, false negative represents a tree that is not detected and assigned to a nearby tree, and false positive represents that a point or pixel cluster is segmented as a tree that does not in fact exist. They respectively represent correct-, under-, and over-segmentation. Three types of index are compared for segmenting individual tree
Grow--a computer subroutine that projects the growth of trees in the Lake States' forests.
Gary J. Brand
1981-01-01
A computer subroutine, Grow, has been written in 1977 Standard FORTRAN to implement a distance-independent, individual tree growth model for Lake States' forests. Grow is a small and easy-to-use version of the growth model. All the user has to do is write a calling program to read initial conditions, call Grow, and summarize the results.
Ali, Arshad; Mattsson, Eskil
2017-01-01
Individual tree size variation, which is generally quantified by variances in tree diameter at breast height (DBH) and height in isolation or conjunction, plays a central role in ecosystem functioning in both controlled and natural environments, including forests. However, none of the studies have been conducted in homegarden agroforestry systems. In this study, aboveground biomass, stand quality, cation exchange capacity (CEC), DBH variation, and species diversity were determined across 45 homegardens in the dry zone of Sri Lanka. We employed structural equation modeling (SEM) to test for the direct and indirect effects of stand quality and CEC, via tree size inequality and species diversity, on aboveground biomass. The SEM accounted for 26, 8, and 1% of the variation in aboveground biomass, species diversity and DBH variation, respectively. DBH variation had the strongest positive direct effect on aboveground biomass (β=0.49), followed by the non-significant direct effect of species diversity (β=0.17), stand quality (β=0.17) and CEC (β=-0.05). There were non-significant direct effects of CEC and stand quality on DBH variation and species diversity. Stand quality and CEC had also non-significant indirect effects, via DBH variation and species diversity, on aboveground biomass. Our study revealed that aboveground biomass substantially increased with individual tree size variation only, which supports the niche complementarity mechanism. However, aboveground biomass was not considerably increased with species diversity, stand quality and soil fertility, which might be attributable to the adaptation of certain productive species to the local site conditions. Stand structure shaped by few productive species or independent of species diversity is a main determinant for the variation in aboveground biomass in the studied homegardens. Maintaining stand structure through management practices could be an effective approach for enhancing aboveground biomass in these dry
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Grigorijs Goldbergs
2018-01-01
Full Text Available The reliability of airborne light detection and ranging (LiDAR for delineating individual trees and estimating aboveground biomass (AGB has been proven in a diverse range of ecosystems, but can be difficult and costly to commission. Point clouds derived from structure from motion (SfM matching techniques obtained from unmanned aerial systems (UAS could be a feasible low-cost alternative to airborne LiDAR scanning for canopy parameter retrieval. This study assesses the extent to which SfM three-dimensional (3D point clouds—obtained from a light-weight mini-UAS quadcopter with an inexpensive consumer action GoPro camera—can efficiently and effectively detect individual trees, measure tree heights, and provide AGB estimates in Australian tropical savannas. Two well-established canopy maxima and watershed segmentation tree detection algorithms were tested on canopy height models (CHM derived from SfM imagery. The influence of CHM spatial resolution on tree detection accuracy was analysed, and the results were validated against existing high-resolution airborne LiDAR data. We found that the canopy maxima and watershed segmentation routines produced similar tree detection rates (~70% for dominant and co-dominant trees, but yielded low detection rates (<35% for suppressed and small trees due to poor representativeness in point clouds and overstory occlusion. Although airborne LiDAR provides higher tree detection rates and more accurate estimates of tree heights, we found SfM image matching to be an adequate low-cost alternative for the detection of dominant and co-dominant tree stands.
Modeling Exponential Population Growth
McCormick, Bonnie
2009-01-01
The concept of population growth patterns is a key component of understanding evolution by natural selection and population dynamics in ecosystems. The National Science Education Standards (NSES) include standards related to population growth in sections on biological evolution, interdependence of organisms, and science in personal and social…
Stand and individual tree growth response to treatments in young natural hardwoods
Daniel J. Robison; Tracy San Filipo; Charlie Lawrence III; Jamie L. Schuler; Bryan J. Berenguer
2012-01-01
Young even-aged upland Piedmont mixed hardwood and pine stands were treated with a variety of fertilizer and release (competition control) treatments. The sites studied are on the NC State University Hill Demonstration Forest in central North Carolina, and are characterized by formerly highly eroded agricultural sites (Richter et al. 2000) now in their third rotation...
Dobbertin, M.; Solberg, S.; Laubhann, D.; Sterba, H.; Reinds, G. J.; de Vries, W.
2009-04-01
Most recent studies show increasing forest growth in central Europe, rather than a decline as was expected due to negative effects of air pollution. While nitrogen deposition, increasing temperature and change in forest management are discussed as possible causes, quantification of the various environmental factors has rarely been undertaken. In our study, we used data from several hundreds of intensive monitoring plots from the ICP Forests network in Europe, ranging from northern Finland to Spain and southern Italy. Five-year growth data for the period 1994-1999 were available from roughly 650 plots to examine the influence of environmental factors on forest growth. Evaluations focused on the influence of nitrogen, sulphur and acid deposition, temperature, precipitation and drought. Concerning the latter meteorological variables we used the deviation from the long-term (30 years) mean. The study included the main tree species common beech (Fagus sylvatica), sessile or pedunculate oak (Quercus petraea and Q. robur), Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Two very different approaches were used. In the first approach an individual tree-based regression model was applied (Laubhahn et al., 2009), while in the second approach a stand-based model was applied (Solberg et al., 2009). The individual tree-based model had measured basal area increment of each individual tree as a growth response variable and tree size (diameter at breast height), tree competition (basal area of larger trees and stand density index), site factors (e.g. soil C/N ratio, temperature), and environmental factors (e.g. temperature change compared to long-term average, nitrogen and sulphur deposition) as influencing parameters. In the stand-growth model, stem volume increment was used as the growth response variable, after filtering out the expected growth. Expected growth was modelled as a function of site productivity, stand age and a stand density index. Relative volume
Automated estimation of leaf distribution for individual trees based on TLS point clouds
Koma, Zsófia; Rutzinger, Martin; Bremer, Magnus
2017-04-01
Light Detection and Ranging (LiDAR) especially the ground based LiDAR (Terrestrial Laser Scanning - TLS) is an operational used and widely available measurement tool supporting forest inventory updating and research in forest ecology. High resolution point clouds from TLS already represent single leaves which can be used for a more precise estimation of Leaf Area Index (LAI) and for higher accurate biomass estimation. However, currently the methodology for extracting single leafs from the unclassified point clouds for individual trees is still missing. The aim of this study is to present a novel segmentation approach in order to extract single leaves and derive features related to leaf morphology (such as area, slope, length and width) of each single leaf from TLS point cloud data. For the study two exemplary single trees were scanned in leaf-on condition on the university campus of Innsbruck during calm wind conditions. A northern red oak (Quercus rubra) was scanned by a discrete return recording Optech ILRIS-3D TLS scanner and a tulip tree (Liliodendron tulpifera) with Riegl VZ-6000 scanner. During the scanning campaign a reference dataset was measured parallel to scanning. In this case 230 leaves were randomly collected around the lower branches of the tree and photos were taken. The developed workflow steps were the following: in the first step normal vectors and eigenvalues were calculated based on the user specified neighborhood. Then using the direction of the largest eigenvalue outliers i.e. ghost points were removed. After that region growing segmentation based on the curvature and angles between normal vectors was applied on the filtered point cloud. On each segment a RANSAC plane fitting algorithm was applied in order to extract the segment based normal vectors. Using the related features of the calculated segments the stem and branches were labeled as non-leaf and other segments were classified as leaf. The validation of the different segmentation
International Nuclear Information System (INIS)
Makela, A.
2003-01-01
A generally accepted method has not emerged for managing the different temporal and spatial scales in a forest ecosystem. This paper reviews a hierarchical-modular modelling tradition, with the main focus on individual tree growth throughout the rotation. At this scale, model performance requires (i) realistic long-term dynamic properties, (ii) realistic responses of growth and mortality of competing individuals, and (iii) realistic responses to ecophysio-logical inputs. Model development and validation are illustrated through allocation patterns, height growth, and size-related feedbacks. Empirical work to test the approach is reviewed. In this approach, finer scale effects are embedded in parameters calculated using more detailed, interacting modules. This is exemplified by (i) the within-year effect of weather on annual photosynthesis, (ii) the effects of fast soil processes on carbon allocation and photosynthesis, and (iii) the utilization of detailed stem structure to predict wood quality. Prevailing management paradigms are reflected in growth modelling. A shift of emphasis has occurred from productivity in homogeneous canopies towards, e.g., wood quality versus total yield, spatially more explicit models, and growth decline in old-growth forests. The new problems emphasize the hierarchy of the system and interscale interactions, suggesting that the hierarchical-modular approach could prove constructive. (author)
Canopy Fuel Load Mapping of Mediterranean Pine Sites Based on Individual Tree-Crown Delineation
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Giorgos Mallinis
2013-12-01
Full Text Available This study presents an individual tree-crown-based approach for canopy fuel load estimation and mapping in two Mediterranean pine stands. Based on destructive sampling, an allometric equation was developed for the estimation of crown fuel weight considering only pine crown width, a tree characteristic that can be estimated from passive imagery. Two high resolution images were used originally for discriminating Aleppo and Calabrian pines crown regions through a geographic object based image analysis approach. Subsequently, the crown region images were segmented using a watershed segmentation algorithm and crown width was extracted. The overall accuracy of the tree crown isolation expressed through a perfect match between the reference and the delineated crowns was 34.00% for the Kassandra site and 48.11% for the Thessaloniki site, while the coefficient of determination between the ground measured and the satellite extracted crown width was 0.5. Canopy fuel load values estimated in the current study presented mean values from 1.29 ± 0.6 to 1.65 ± 0.7 kg/m2 similar to other conifers worldwide. Despite the modest accuracies attained in this first study of individual tree crown fuel load mapping, the combination of the allometric equations with satellite-based extracted crown width information, can contribute to the spatially explicit mapping of canopy fuel load in Mediterranean areas. These maps can be used among others in fire behavior prediction, in fuel reduction treatments prioritization and during active fire suppression.
Lidar-based individual tree species classification using convolutional neural network
Mizoguchi, Tomohiro; Ishii, Akira; Nakamura, Hiroyuki; Inoue, Tsuyoshi; Takamatsu, Hisashi
2017-06-01
Terrestrial lidar is commonly used for detailed documentation in the field of forest inventory investigation. Recent improvements of point cloud processing techniques enabled efficient and precise computation of an individual tree shape parameters, such as breast-height diameter, height, and volume. However, tree species are manually specified by skilled workers to date. Previous works for automatic tree species classification mainly focused on aerial or satellite images, and few works have been reported for classification techniques using ground-based sensor data. Several candidate sensors can be considered for classification, such as RGB or multi/hyper spectral cameras. Above all candidates, we use terrestrial lidar because it can obtain high resolution point cloud in the dark forest. We selected bark texture for the classification criteria, since they clearly represent unique characteristics of each tree and do not change their appearance under seasonable variation and aged deterioration. In this paper, we propose a new method for automatic individual tree species classification based on terrestrial lidar using Convolutional Neural Network (CNN). The key component is the creation step of a depth image which well describe the characteristics of each species from a point cloud. We focus on Japanese cedar and cypress which cover the large part of domestic forest. Our experimental results demonstrate the effectiveness of our proposed method.
Modeling Population Growth and Extinction
Gordon, Sheldon P.
2009-01-01
The exponential growth model and the logistic model typically introduced in the mathematics curriculum presume that a population grows exclusively. In reality, species can also die out and more sophisticated models that take the possibility of extinction into account are needed. In this article, two extensions of the logistic model are considered,…
Stochastic models for tumoral growth
Escudero, Carlos
2006-02-01
Strong experimental evidence has indicated that tumor growth belongs to the molecular beam epitaxy universality class. This type of growth is characterized by the constraint of cell proliferation to the tumor border and the surface diffusion of cells at the growing edge. Tumor growth is thus conceived as a competition for space between the tumor and the host, and cell diffusion at the tumor border is an optimal strategy adopted for minimizing the pressure and helping tumor development. Two stochastic partial differential equations are reported in this paper in order to correctly model the physical properties of tumoral growth in (1+1) and (2+1) dimensions. The advantage of these models is that they reproduce the correct geometry of the tumor and are defined in terms of polar variables. An analysis of these models allows us to quantitatively estimate the response of the tumor to an unfavorable perturbation during growth.
Towards Sustainable Growth Business Models
Energy Technology Data Exchange (ETDEWEB)
Kamp-Roelands, N.; Balkenende, J.P.; Van Ommen, P.
2012-03-15
The Dutch Sustainable Growth Coalition (DSGC) has the following objectives: The DSGC aims to pro-actively drive sustainable growth business models along three lines: (1) Shape. DSGC member companies aim to connect economic profitability with environmental and social progress on the basis of integrated sustainable growth business models; (2) Share. DSGC member companies aim for joint advocacy of sustainable growth business models both internationally and nationally; and (3) Stimulate. DSGC member companies aim to stimulate and influence the policy debate on enabling sustainable growth - with a view to finding solutions to the environmental and social challenges we are facing. This is their first report. The vision, actions and mission of DSGC are documented in the Manifesto in Chapter 2 of this publication. Chapter 3 contains an overview of key features of an integrated sustainable growth business model and the roadmap towards such a model. In Chapter 4, project examples of DSGC members are presented, providing insight into the hands-on reality of implementing the good practices. Chapter 5 offers an overview of how the Netherlands provides an enabling environment for sustainable growth business models. Chapter 6 offers the key conclusions.
Trends in Automatic Individual Tree Crown Detection and Delineation—Evolution of LiDAR Data
Directory of Open Access Journals (Sweden)
Zhen Zhen
2016-04-01
Full Text Available Automated individual tree crown detection and delineation (ITCD using remotely sensed data plays an increasingly significant role in efficiently, accurately, and completely monitoring forests. This paper reviews trends in ITCD research from 1990–2015 from several perspectives—data/forest type, method applied, accuracy assessment and research objective—with a focus on studies using LiDAR data. This review shows that active sources are becoming more prominent in ITCD studies. Studies using active data—LiDAR in particular—accounted for 80% of the total increase over the entire time period, those using passive data or fusion of passive and active data comprised relatively small proportions of the total increase (8% and 12%, respectively. Additionally, ITCD research has moved from incremental adaptations of algorithms developed for passive data sources to innovative approaches that take advantage of the novel characteristics of active datasets like LiDAR. These improvements make it possible to explore more complex forest conditions (e.g., closed hardwood forests, suburban/urban forests rather than a single forest type although most published ITCD studies still focused on closed softwood (41% or mixed forest (22%. Approximately one-third of studies applied individual tree level (30% assessment, with only a quarter reporting more comprehensive multi-level assessment (23%. Almost one-third of studies (32% that concentrated on forest parameter estimation based on ITCD results had no ITCD-specific evaluation. Comparison of methods continues to be complicated by both choice of reference data and assessment metric; it is imperative to establish a standardized two-level assessment framework to evaluate and compare ITCD algorithms in order to provide specific recommendations about suitable applications of particular algorithms. However, the evolution of active remotely sensed data and novel platforms implies that automated ITCD will continue to be a
Model uncertainty in growth empirics
Prüfer, P.
2008-01-01
This thesis applies so-called Bayesian model averaging (BMA) to three different economic questions substantially exposed to model uncertainty. Chapter 2 addresses a major issue of modern development economics: the analysis of the determinants of pro-poor growth (PPG), which seeks to combine high
Bressan, Alberto; Lewicka, Marta
2018-03-01
We consider a free boundary problem for a system of PDEs, modeling the growth of a biological tissue. A morphogen, controlling volume growth, is produced by specific cells and then diffused and absorbed throughout the domain. The geometric shape of the growing tissue is determined by the instantaneous minimization of an elastic deformation energy, subject to a constraint on the volumetric growth. For an initial domain with C}^{2,α boundary, our main result establishes the local existence and uniqueness of a classical solution, up to a rigid motion.
Low Tree-Growth Elasticity of Forest Biomass Indicated by an Individual-Based Model
Directory of Open Access Journals (Sweden)
Robbie A. Hember
2018-01-01
Full Text Available Environmental conditions and silviculture fundamentally alter the metabolism of individual trees and, therefore, need to be studied at that scale. However, changes in forest biomass density (Mg C ha−1 may be decoupled from changes in growth (kg C year−1 when the latter also accelerates the life cycle of trees and strains access to light, nutrients, and water. In this study, we refer to an individual-based model of forest biomass dynamics to constrain the magnitude of system feedbacks associated with ontogeny and competition and estimate the scaling relationship between changes in tree growth and forest biomass density. The model was driven by fitted equations of annual aboveground biomass growth (Gag, probability of recruitment (Pr, and probability of mortality (Pm parameterized against field observations of black spruce (Picea mariana (Mill. BSP, interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn. Franco, and western hemlock (Tsuga heterophylla (Raf. Sarg.. A hypothetical positive step-change in mean tree growth was imposed half way through the simulations and landscape-scale responses were then evaluated by comparing pre- and post-stimulus periods. Imposing a 100% increase in tree growth above calibrated predictions (i.e., contemporary rates only translated into 36% to 41% increases in forest biomass density. This corresponded with a tree-growth elasticity of forest biomass (εG,SB ranging from 0.33 to 0.55. The inelastic nature of stand biomass density was attributed to the dependence of mortality on intensity of competition and tree size, which decreased stand density by 353 to 495 trees ha−1, and decreased biomass residence time by 10 to 23 years. Values of εG,SB depended on the magnitude of the stimulus. For example, a retrospective scenario in which tree growth increased from 50% below contemporary rates up to contemporary rates indicated values of εG,SB ranging from 0.66 to 0.75. We conclude that: (1 effects of
The Validation of the Mixedwood Growth Model (MGM for Use in Forest Management Decision Making
Directory of Open Access Journals (Sweden)
Mike Bokalo
2013-01-01
Full Text Available We evaluated the Mixedwood Growth Model (MGM at a whole model scale for pure and mixed species stands of aspen and white spruce in the western boreal forest. MGM is an individual tree-based, distance-independent growth model, designed to evaluate growth and yield implications relating to the management of white spruce, black spruce, aspen, lodgepole pine, and mixedwood stands in Alberta, British Columbia, Saskatchewan, and Manitoba. Our validation compared stand-level model predictions against re-measured data (volume, basal area, diameter at breast height (DBH, average and top height and density from permanent sample plots using combined analysis of residual plots, bias statistics, efficiency and an innovative application of the equivalence test. For state variables, the model effectively simulated juvenile and mature stages of stand development for both pure and mixed species stands of aspen and white spruce in Alberta. MGM overestimates increment in older stands likely due to age-related pathology and weather-related stand damage. We identified underestimates of deciduous density and volume in Saskatchewan. MGM performs well for increment in postharvest stands less than 30 years of age. These results illustrate the comprehensive application of validation metrics to evaluate a complex model, and provide support for the use of MGM in management planning.
Mudcake growth: Model and implications
Liu, Q.; Santamarina, Carlos
2017-01-01
cementing, and to prevent partial differential sticking. We developed a robust mud cake growth model for water-based mud based on wide stress-range constitutive equations within a Lagrangian reference system to avoid non-natural moving boundary solutions
A simple photographical method for analyzing the radiation interception by an individual tree
International Nuclear Information System (INIS)
Elsacker, P. van; Keppens, H.; Impens, I.
1983-01-01
A method for analyzing radiation interception by an individual tree is presented. The use of a whole set of expensive radiation instruments is eliminated, the work-intensive field experiments are reduced to half a day for a large tree (9 m), and neither clear sky conditions nor diffuse radiation data are necessary. It is assumed that for a given azimuth and solar elevation the shading caused by a tree can be estimated photographically by taking a slide in the opposite direction. From slides taken of the whole tree in different directions and from different distances (i.e., different view angles), gap frequencies for certain heights are measured. At each height, gap frequency decreases significantly with increasing solar elevation. By calculating the mean path length within the crown (s) corresponding with each gap frequency (g), a highly significant exponential relationship between both is obtained [g = exp(−0.42s)]. With this equation and by knowing the tree dimensions calculated from the slides, direct and diffuse radiation interception of the whole tree can be estimated. Total leaf area and leaf area density are also calculated. These values agree very well with direct measurements on similar cut trees
Directory of Open Access Journals (Sweden)
Sebastian Lamprecht
2017-05-01
Full Text Available Determining the exact position of a forest inventory plot—and hence the position of the sampled trees—is often hampered by a poor Global Navigation Satellite System (GNSS signal quality beneath the forest canopy. Inaccurate geo-references hamper the performance of models that aim to retrieve useful information from spatially high remote sensing data (e.g., species classification or timber volume estimation. This restriction is even more severe on the level of individual trees. The objective of this study was to develop a post-processing strategy to improve the positional accuracy of GNSS-measured sample-plot centers and to develop a method to automatically match trees within a terrestrial sample plot to aerial detected trees. We propose a new method which uses a random forest classifier to estimate the matching probability of each terrestrial-reference and aerial detected tree pair, which gives the opportunity to assess the reliability of the results. We investigated 133 sample plots of the Third German National Forest Inventory (BWI, 2011–2012 within the German federal state of Rhineland-Palatinate. For training and objective validation, synthetic forest stands have been modeled using the Waldplaner 2.0 software. Our method has achieved an overall accuracy of 82.7% for co-registration and 89.1% for tree matching. With our method, 60% of the investigated plots could be successfully relocated. The probabilities provided by the algorithm are an objective indicator of the reliability of a specific result which could be incorporated into quantitative models to increase the performance of forest attribute estimations.
Yankine, S. A.; Van Stan, J. T., II; Mesta, D. C.; Côté, J. F.; Hildebrandt, A.; Friesen, J.; Maldonado, G.
2017-12-01
Stemflow is a pointed hydrologic flux at the base of tree stems that has been linked to a host of biogeochemical processes in vegetated landscapes. Much work has been done to examine controls over stemflow water yield, finding three major factors: individual tree canopy structure, meteorological variables, and neighborhood conditions. However, the authors are unaware of any study to directly quantify all factors using a combination of terrestrial LiDAR and micrometeorological monitoring methods. This study directly quantifies individual Pinus palustris tree canopy characteristics (trunk volume and angle, branch volume and angle from 1st-to-3rd order, bark roughness, and height), 10-m radius neighborhood properties (number of trees, mean diameter and height, mean distance from study tree, and canopy overlap), and above-canopy storm conditions (magnitude, intensity, mean/max wind speed, and vapor pressure deficit) directly at the site. Stemflow production was 1% of rainfall, ranging from 0.3-59 L per storm from individual trees. Preliminary findings from storms (5-176 mm in magnitude) indicate that all individual tree characteristics, besides bark roughness, have little influence on stemflow generation. Bark roughness altered stemflow generation by affecting trunk water storage (0.1-0.7 mm) and wet trunk evaporation rates (0.005-0.03 mm/h). The strongest influence over stemflow generation from individual trees was the interaction between neighborhood characteristics and meteorological conditions (primarily rainfall amount and, secondarily, rainfall intensity).
Tyson L. Swetnam; Donald A. Falk; Ann M. Lynch; Stephen R. Yool
2014-01-01
Limitations inherent to airborne laser scanning (ALS) technology and the complex sorting and packing relationships of forests complicate accurate remote sensing of mid- and understory trees, especially in denser forest stands. Self-similarities in rank-sized individual tree distributions (ITD), e.g. bole diameter or height, are a well-understood property of natural,...
Individual tree crown modeling and change detection from airborne lidar data
Xiao, W.; Xu, Sudan; Oude Elberink, S.J.; Vosselman, G.
2016-01-01
Light detection and ranging (lidar) provides a promising way of detecting changes of trees in three-dimensional (3-D) because laser beams can penetrate through the foliage and therefore provide full coverage of trees. The aim is to detect changes in trees in urban areas using multitemporal airborne
Viscoelastic model of tungsten 'fuzz' growth
International Nuclear Information System (INIS)
Krasheninnikov, S I
2011-01-01
A viscoelastic model of fuzz growth is presented. The model describes the main features of tungsten fuzz observed in experiments. It gives estimates of fuzz growth rate and temperature range close to experimental ones.
Stand model for upland forests of Southern Arkansas
Energy Technology Data Exchange (ETDEWEB)
Mielke, D.L.; Shugart, H.H.; West, D.C.
1978-06-01
A forest stand growth and composition simulator (FORAR) was developed by modifying a stand growth model by Shugart and West (1977). FORAR is a functional stand model which used ecological parameters to relate individual tree growth to environment rather than using Markov probability matrices or differential equations to determine single tree or species replacement rates. FORAR simulated tree growth and species composition of upland forests of Union County, Ark., by considering 33 tree species on a /sup 1///sub 12/ ha circular plot.
"Growing trees backwards": Description of a stand reconstruction model
Jonathan D. Bakker; Andrew J. Sanchez Meador; Peter Z. Fule; David W. Huffman; Margaret M. Moore
2008-01-01
We describe an individual-tree model that uses contemporary measurements to "grow trees backward" and reconstruct past tree diameters and stand structure in ponderosa pine dominated stands of the Southwest. Model inputs are contemporary structural measurements of all snags, logs, stumps, and living trees, and radial growth measurements, if available. Key...
Mudcake growth: Model and implications
Liu, Q.
2017-12-15
Oil and gas account for 60% of the world\\'s energy consumption. Drilling muds that are used to advance oil and gas wells must be engineered to avoid wellbore integrity problems associated with mud cake formation, to favor cake erosion during cementing, and to prevent partial differential sticking. We developed a robust mud cake growth model for water-based mud based on wide stress-range constitutive equations within a Lagrangian reference system to avoid non-natural moving boundary solutions. The comprehensive mud cake growth model readily accommodates environmental factors (e.g., temperature, pH, and ionic concentration) and defines the yield stress distribution for displacement-erosion analyses. Results show that the mud cake thickness is more sensitive to time than to filtration pressure, therefore, time controls the non-uniform distribution of mudcake thickness during drilling. Long filtration time, high permeability, high salinity, high in-situ temperature and low viscosity exacerbate fluid loss and give rise to thick filter cakes. The analysis of residual cake thickness during cement displacement must take into account the effective stress dependent mudcake formation and the time-dependent mud thixotropy. Thixotropy dominates the mud yield stress at high void ratios, e.g. e > 20. The offsetting force that causes differential pressure sticking increases sub-linearly as a power function of the still-time.
A model for predicting the growth of Eucalyptus globulus seedling stands in Bolivia
Energy Technology Data Exchange (ETDEWEB)
Guzman, G.; Morales, M.; Pukkala, T.; Miguel, S. de
2012-11-01
Eucalyptus globulus is one of the most planted species in the Inter-Andean Valleys of Bolivia, where growing conditions are different from most places where eucalyptus have been studied. This prevents a straightforward utilization of models fitted elsewhere. In this study a distance-independent individual-tree growth model for E. globulus plantations in Bolivia was developed based on data from 67 permanent sample plots. The model consists of sub-models for dominant height, tree diameter increment, height-diameter relationship and survival. According to model-based simulations, the mean annual increment with the optimal rotation length is about 13 m3 ha{sup -}1 yr{sup -}1 on medium-quality sites and 18 m{sup 3} ha{sup -}1 yr -1 on the best sites. A suitable rotation length for maximizing wood production is approximately 30 years on medium sites and 20 years on the most productive sites. The developed models provide valuable information for further studies on optimizing the management and evaluating alternative management regimes for the species. (Author) 22 refs.
Directory of Open Access Journals (Sweden)
Y. Takenaka
2017-10-01
Full Text Available Pine wilt disease is caused by the pine wood nematode (Bursaphelenchus xylophilus and Japanese pine sawyer (Monochamus alternatus. This study attempted to detect damaged pine trees at different levels using a combination of airborne laser scanning (ALS data and high-resolution space-borne images. A canopy height model with a resolution of 50 cm derived from the ALS data was used for the delineation of tree crowns using the Individual Tree Detection method. Two pan-sharpened images were established using the ortho-rectified images. Next, we analyzed two kinds of intensity-hue-saturation (IHS images and 18 remote sensing indices (RSI derived from the pan-sharpened images. The mean and standard deviation of the 2 IHS images, 18 RSI, and 8 bands of the WV-2 and WV-3 images were extracted for each tree crown and were used to classify tree crowns using a support vector machine classifier. Individual tree crowns were assigned to one of nine classes: bare ground, Larix kaempferi, Cryptomeria japonica, Chamaecyparis obtusa, broadleaved trees, healthy pines, and damaged pines at slight, moderate, and heavy levels. The accuracy of the classifications using the WV-2 images ranged from 76.5 to 99.6 %, with an overall accuracy of 98.5 %. However, the accuracy of the classifications using the WV-3 images ranged from 40.4 to 95.4 %, with an overall accuracy of 72 %, which suggests poorer accuracy compared to those classes derived from the WV-2 images. This is because the WV-3 images were acquired in October 2016 from an area with low sun, at a low altitude.
Mathematical modeling of microbial growth in milk
Directory of Open Access Journals (Sweden)
Jhony Tiago Teleken
2011-12-01
Full Text Available A mathematical model to predict microbial growth in milk was developed and analyzed. The model consists of a system of two differential equations of first order. The equations are based on physical hypotheses of population growth. The model was applied to five different sets of data of microbial growth in dairy products selected from Combase, which is the most important database in the area with thousands of datasets from around the world, and the results showed a good fit. In addition, the model provides equations for the evaluation of the maximum specific growth rate and the duration of the lag phase which may provide useful information about microbial growth.
Latent Growth and Dynamic Structural Equation Models.
Grimm, Kevin J; Ram, Nilam
2018-05-07
Latent growth models make up a class of methods to study within-person change-how it progresses, how it differs across individuals, what are its determinants, and what are its consequences. Latent growth methods have been applied in many domains to examine average and differential responses to interventions and treatments. In this review, we introduce the growth modeling approach to studying change by presenting different models of change and interpretations of their model parameters. We then apply these methods to examining sex differences in the development of binge drinking behavior through adolescence and into adulthood. Advances in growth modeling methods are then discussed and include inherently nonlinear growth models, derivative specification of growth models, and latent change score models to study stochastic change processes. We conclude with relevant design issues of longitudinal studies and considerations for the analysis of longitudinal data.
Aubry-Kientz, Mélaine; Rossi, Vivien; Boreux, Jean-Jacques; Hérault, Bruno
2015-06-01
Tree vigor is often used as a covariate when tree mortality is predicted from tree growth in tropical forest dynamic models, but it is rarely explicitly accounted for in a coherent modeling framework. We quantify tree vigor at the individual tree level, based on the difference between expected and observed growth. The available methods to join nonlinear tree growth and mortality processes are not commonly used by forest ecologists so that we develop an inference methodology based on an MCMC approach, allowing us to sample the parameters of the growth and mortality model according to their posterior distribution using the joint model likelihood. We apply our framework to a set of data on the 20-year dynamics of a forest in Paracou, French Guiana, taking advantage of functional trait-based growth and mortality models already developed independently. Our results showed that growth and mortality are intimately linked and that the vigor estimator is an essential predictor of mortality, highlighting that trees growing more than expected have a far lower probability of dying. Our joint model methodology is sufficiently generic to be used to join two longitudinal and punctual linked processes and thus may be applied to a wide range of growth and mortality models. In the context of global changes, such joint models are urgently needed in tropical forests to analyze, and then predict, the effects of the ongoing changes on the tree dynamics in hyperdiverse tropical forests.
Modelling dwarf mistletoe at three scales: life history, ballistics and contagion
Donald C. E. Robinson; Brian W. Geils
2006-01-01
The epidemiology of dwarf mistletoe (Arceuthobium) is simulated for the reproduction, dispersal, and spatial patterns of these plant pathogens on conifer trees. A conceptual model for mistletoe spread and intensification is coded as sets of related subprograms that link to either of two individual-tree growth models (FVS and TASS) used by managers to develop...
"Growing trees backwards": Description of a stand reconstruction model (P-53)
Jonathan D. Bakker; Andrew J. Sanchez Meador; Peter Z. Fule; David W. Huffman; Margaret M. Moore
2008-01-01
We describe an individual-tree model that uses contemporary measurements to "grow trees backward" and reconstruct past tree diameters and stand structure in ponderosa pine dominated stands of the Southwest. Model inputs are contemporary structural measurements of all snags, logs, stumps, and living trees, and radial growth measurements, if available. Key...
DEFF Research Database (Denmark)
Jónsdóttir, Kristjana Ýr; Schmiegel, Jürgen; Jensen, Eva Bjørn Vedel
2008-01-01
In the present paper, we give a condensed review, for the nonspecialist reader, of a new modelling framework for spatio-temporal processes, based on Lévy theory. We show the potential of the approach in stochastic geometry and spatial statistics by studying Lévy-based growth modelling of planar o...... objects. The growth models considered are spatio-temporal stochastic processes on the circle. As a by product, flexible new models for space–time covariance functions on the circle are provided. An application of the Lévy-based growth models to tumour growth is discussed....
Stochastic models for tumoral growth
Escudero, Carlos
2006-01-01
Strong experimental evidence has indicated that tumor growth belongs to the molecular beam epitaxy universality class. This type of growth is characterized by the constraint of cell proliferation to the tumor border, and surface diffusion of cells at the growing edge. Tumor growth is thus conceived as a competition for space between the tumor and the host, and cell diffusion at the tumor border is an optimal strategy adopted for minimizing the pressure and helping tumor development. Two stoch...
Mechanistic model for microbial growth on hydrocarbons
Energy Technology Data Exchange (ETDEWEB)
Mallee, F M; Blanch, H W
1977-12-01
Based on available information describing the transport and consumption of insoluble alkanes, a mechanistic model is proposed for microbial growth on hydrocarbons. The model describes the atypical growth kinetics observed, and has implications in the design of large scale equipment for single cell protein (SCP) manufacture from hydrocarbons. The model presents a framework for comparison of the previously published experimental kinetic data.
Testing mechanistic models of growth in insects.
Maino, James L; Kearney, Michael R
2015-11-22
Insects are typified by their small size, large numbers, impressive reproductive output and rapid growth. However, insect growth is not simply rapid; rather, insects follow a qualitatively distinct trajectory to many other animals. Here we present a mechanistic growth model for insects and show that increasing specific assimilation during the growth phase can explain the near-exponential growth trajectory of insects. The presented model is tested against growth data on 50 insects, and compared against other mechanistic growth models. Unlike the other mechanistic models, our growth model predicts energy reserves per biomass to increase with age, which implies a higher production efficiency and energy density of biomass in later instars. These predictions are tested against data compiled from the literature whereby it is confirmed that insects increase their production efficiency (by 24 percentage points) and energy density (by 4 J mg(-1)) between hatching and the attainment of full size. The model suggests that insects achieve greater production efficiencies and enhanced growth rates by increasing specific assimilation and increasing energy reserves per biomass, which are less costly to maintain than structural biomass. Our findings illustrate how the explanatory and predictive power of mechanistic growth models comes from their grounding in underlying biological processes. © 2015 The Author(s).
Trajectories and models of individual growth
Directory of Open Access Journals (Sweden)
Arseniy Karkach
2006-11-01
Full Text Available It has long been recognized that the patterns of growth play an important role in the evolution of age trajectories of fertility and mortality (Williams, 1957. Life history studies would benefit from a better understanding of strategies and mechanisms of growth, but still no comparative research on individual growth strategies has been conducted. Growth patterns and methods have been shaped by evolution and a great variety of them are observed. Two distinct patterns - determinate and indeterminate growth - are of a special interest for these studies since they present qualitatively different outcomes of evolution. We attempt to draw together studies covering growth in plant and animal species across a wide range of phyla focusing primarily on the noted qualitative features. We also review mathematical descriptions of growth, namely empirical growth curves and growth models, and discuss the directions of future research.
Nonconvex Model of Material Growth: Mathematical Theory
Ganghoffer, J. F.; Plotnikov, P. I.; Sokolowski, J.
2018-06-01
The model of volumetric material growth is introduced in the framework of finite elasticity. The new results obtained for the model are presented with complete proofs. The state variables include the deformations, temperature and the growth factor matrix function. The existence of global in time solutions for the quasistatic deformations boundary value problem coupled with the energy balance and the evolution of the growth factor is shown. The mathematical results can be applied to a wide class of growth models in mechanics and biology.
Pollution externalities in a Schumpeterian growth model
Koesler, Simon
2010-01-01
This paper extends a standard Schumpeterian growth model to include an environmental dimension. Thereby, it explicitly links the pollution intensity of economic activity to technological progress. In a second step, it investigates the effect of pollution on economic growth under the assumption that pollution intensities are related to technological progress. Several conclusions emerge from the model. In equilibrium, the economy follows a balanced growth path. The effect of pollution on the ec...
Sawyer S. Scherer; Anthony W. D' Amato; Christel C. Kern; Brian J. Palik; Matthew B. Russell
2016-01-01
Prescribed fire is increasingly being viewed as a valuable tool for mitigating the ecological consequences of long-term fire suppression within fire-adapted forest ecosystems. While the use of burning treatments in northern temperate conifer forests has at times received considerable attention, the long-term (>10 years) effects on forest structure and...
Modelling asymmetric growth in crowded plant communities
DEFF Research Database (Denmark)
Damgaard, Christian
2010-01-01
A class of models that may be used to quantify the effect of size-asymmetric competition in crowded plant communities by estimating a community specific degree of size-asymmetric growth for each species in the community is suggested. The model consists of two parts: an individual size......-asymmetric growth part, where growth is assumed to be proportional to a power function of the size of the individual, and a term that reduces the relative growth rate as a decreasing function of the individual plant size and the competitive interactions from other plants in the neighbourhood....
Growth curve models and statistical diagnostics
Pan, Jian-Xin
2002-01-01
Growth-curve models are generalized multivariate analysis-of-variance models. These models are especially useful for investigating growth problems on short times in economics, biology, medical research, and epidemiology. This book systematically introduces the theory of the GCM with particular emphasis on their multivariate statistical diagnostics, which are based mainly on recent developments made by the authors and their collaborators. The authors provide complete proofs of theorems as well as practical data sets and MATLAB code.
On a Versatile Stochastic Growth Model
Directory of Open Access Journals (Sweden)
Samiur Arif
2012-06-01
Full Text Available Growth phenomena are ubiquitous and pervasive not only in biology and the medical sciences, but also in economics, marketing and the computer and social sciences. We introduce a three-parameter version of the classic pure-birth process growth model when suitably instantiated, can be used to model growth phenomena in many seemingly unrelated application domains. We point out that the model is computationally attractive since it admits of conceptually simple, closed form solutions for the time-dependent probabilities.
Recent advances in modelling creep crack growth
International Nuclear Information System (INIS)
Riedel, H.
1988-08-01
At the time of the previous International Conference on Fracture, the C* integral had long been recognized as a promising load parameter for correlating crack growth rates in creep-ductile materials. The measured crack growth rates as a function of C* and of the temperature could be understood on the basis of micromechanical models. The distinction between C*-controlled and K I -controlled creep crack growth had been clarified and first attempts had been made to describe creep crack growth in the transient regime between elastic behavior and steady-state creep. This paper describes the progress in describing transient crack growth including the effect of primary creep. The effect of crack-tip geometry changes by blunting and by crack growth on the crack-tip fields and on the validity of C* is analyzed by idealizing the growing-crack geometry by a sharp notch and using recent solutions for the notch-tip fields. A few new three-dimensional calculations of C* are cited and important theoretical points are emphasized regarding the three-dimensional fields at crack tips. Finally, creep crack growth is described by continuum-damage models for which similarity solutions can be obtained. Crack growth under small-scale creep conditions turns out to be difficult to understand. Slightly different models yield very different crack growth rates. (orig.) With 4 figs
Kinetic Model of Growth of Arthropoda Populations
Ershov, Yu. A.; Kuznetsov, M. A.
2018-05-01
Kinetic equations were derived for calculating the growth of crustacean populations ( Crustacea) based on the biological growth model suggested earlier using shrimp ( Caridea) populations as an example. The development cycle of successive stages for populations can be represented in the form of quasi-chemical equations. The kinetic equations that describe the development cycle of crustaceans allow quantitative prediction of the development of populations depending on conditions. In contrast to extrapolation-simulation models, in the developed kinetic model of biological growth the kinetic parameters are the experimental characteristics of population growth. Verification and parametric identification of the developed model on the basis of the experimental data showed agreement with experiment within the error of the measurement technique.
Compatible growth models and stand density diagrams
International Nuclear Information System (INIS)
Smith, N.J.; Brand, D.G.
1988-01-01
This paper discusses a stand average growth model based on the self-thinning rule developed and used to generate stand density diagrams. Procedures involved in testing are described and results are included
Value function in economic growth model
Bagno, Alexander; Tarasyev, Alexandr A.; Tarasyev, Alexander M.
2017-11-01
Properties of the value function are examined in an infinite horizon optimal control problem with an unlimited integrand index appearing in the quality functional with a discount factor. Optimal control problems of such type describe solutions in models of economic growth. Necessary and sufficient conditions are derived to ensure that the value function satisfies the infinitesimal stability properties. It is proved that value function coincides with the minimax solution of the Hamilton-Jacobi equation. Description of the growth asymptotic behavior for the value function is provided for the logarithmic, power and exponential quality functionals and an example is given to illustrate construction of the value function in economic growth models.
Tax Evasion and Economic Growth in an Endogenous Growth Model
加藤, 秀弥; KATO, Hideya
2004-01-01
This paper presents an endogenous growth model with tax evasion where government expenditures affect production. An individual evades a tax so as to maximize his or her utility, the tax authority controls the detection probability to maximize net tax revenue, and the government chooses the income tax rate to maximize individuals’ utility. The main conclusions are as follows. First, the optical income tax rate with tax evasion is higher than that without tax evasion. Second, the rise in a ...
Lu, Yi
2016-01-01
To model students' math growth trajectory, three conventional growth curve models and three growth mixture models are applied to the Early Childhood Longitudinal Study Kindergarten-Fifth grade (ECLS K-5) dataset in this study. The results of conventional growth curve model show gender differences on math IRT scores. When holding socio-economic…
McNeish, Daniel; Dumas, Denis
2017-01-01
Recent methodological work has highlighted the promise of nonlinear growth models for addressing substantive questions in the behavioral sciences. In this article, we outline a second-order nonlinear growth model in order to measure a critical notion in development and education: potential. Here, potential is conceptualized as having three components-ability, capacity, and availability-where ability is the amount of skill a student is estimated to have at a given timepoint, capacity is the maximum amount of ability a student is predicted to be able to develop asymptotically, and availability is the difference between capacity and ability at any particular timepoint. We argue that single timepoint measures are typically insufficient for discerning information about potential, and we therefore describe a general framework that incorporates a growth model into the measurement model to capture these three components. Then, we provide an illustrative example using the public-use Early Childhood Longitudinal Study-Kindergarten data set using a Michaelis-Menten growth function (reparameterized from its common application in biochemistry) to demonstrate our proposed model as applied to measuring potential within an educational context. The advantage of this approach compared to currently utilized methods is discussed as are future directions and limitations.
Localisation in a Growth Model with Interaction
Costa, M.; Menshikov, M.; Shcherbakov, V.; Vachkovskaia, M.
2018-05-01
This paper concerns the long term behaviour of a growth model describing a random sequential allocation of particles on a finite cycle graph. The model can be regarded as a reinforced urn model with graph-based interaction. It is motivated by cooperative sequential adsorption, where adsorption rates at a site depend on the configuration of existing particles in the neighbourhood of that site. Our main result is that, with probability one, the growth process will eventually localise either at a single site, or at a pair of neighbouring sites.
Residual Structures in Latent Growth Curve Modeling
Grimm, Kevin J.; Widaman, Keith F.
2010-01-01
Several alternatives are available for specifying the residual structure in latent growth curve modeling. Two specifications involve uncorrelated residuals and represent the most commonly used residual structures. The first, building on repeated measures analysis of variance and common specifications in multilevel models, forces residual variances…
Growth and yield models in Spain: Historical overview, Contemporary Examples and perspectives
Energy Technology Data Exchange (ETDEWEB)
Bravo, F.; Alvarez-Gonzalez, J. G.; Rio, M. del; Barrio, M.; Bonet, J. a.; Bravo-Oviedo, A.; Calama, R.; Castedo-Dorado, F.; Crecente-Campo, F.; Condes, S.; Dieguez-Aranda, U.; Gonzalez-Martinez, S. C.; Lizarralde, I.; Nanos, N.; Madrigal, A.; Martinez-Millan, F. J.; Montero, G.; Ordonez, C.; Palahi, M.; Pique, M.; Rodriguez, F.; Rodriguez-Soalleiro, R.; Rojo, A.; Ruiz-Peinado, R.; Sanchez-Gonzalez, M.; Trasobares, A.; Vazquez-Pique, J.
2011-07-01
In this paper we present a review of forest models developed in Spain in recent years for both timber and non timber production and forest dynamics (regeneration, mortality,..). Models developed are whole stand, size (diameter) class and individual-tree. The models developed to date have been developed using data from permanent plots, experimental sites and the National Forest Inventory. In this paper we show the different sub-models developed so far and the friendly use software. Main perspectives of forest modelling in Spain are presented. (Author) 107 refs.
Thermal models pertaining to continental growth
International Nuclear Information System (INIS)
Morgan, P.; Ashwal, L.
1988-01-01
Thermal models are important to understanding continental growth as the genesis, stabilization, and possible recycling of continental crust are closely related to the tectonic processes of the earth which are driven primarily by heat. The thermal energy budget of the earth was slowly decreasing since core formation, and thus the energy driving the terrestrial tectonic engine was decreasing. This fundamental observation was used to develop a logic tree defining the options for continental growth throughout earth history
Structural modelling of economic growth: Technological changes
Directory of Open Access Journals (Sweden)
Sukharev Oleg
2016-01-01
Full Text Available Neoclassical and Keynesian theories of economic growth assume the use of Cobb-Douglas modified functions and other aggregate econometric approaches to growth dynamics modelling. In that case explanations of economic growth are based on the logic of the used mathematical ratios often including the ideas about aggregated values change and factors change a priori. The idea of assessment of factor productivity is the fundamental one among modern theories of economic growth. Nevertheless, structural parameters of economic system, institutions and technological changes are practically not considered within known approaches, though the latter is reflected in the changing parameters of production function. At the same time, on the one hand, the ratio of structural elements determines the future value of the total productivity of the factors and, on the other hand, strongly influences the rate of economic growth and its mode of innovative dynamics. To put structural parameters of economic system into growth models with the possibility of assessment of such modes under conditions of interaction of new and old combinations is an essential step in the development of the theory of economic growth/development. It allows forming stimulation policy of economic growth proceeding from the structural ratios and relations recognized for this economic system. It is most convenient in such models to use logistic functions demonstrating the resource change for old and new combination within the economic system. The result of economy development depends on starting conditions, and on institutional parameters of velocity change of resource borrowing in favour of a new combination and creation of its own resource. Model registration of the resource is carried out through the idea of investments into new and old combinations.
In silico modeling for tumor growth visualization.
Jeanquartier, Fleur; Jean-Quartier, Claire; Cemernek, David; Holzinger, Andreas
2016-08-08
Cancer is a complex disease. Fundamental cellular based studies as well as modeling provides insight into cancer biology and strategies to treatment of the disease. In silico models complement in vivo models. Research on tumor growth involves a plethora of models each emphasizing isolated aspects of benign and malignant neoplasms. Biologists and clinical scientists are often overwhelmed by the mathematical background knowledge necessary to grasp and to apply a model to their own research. We aim to provide a comprehensive and expandable simulation tool to visualizing tumor growth. This novel Web-based application offers the advantage of a user-friendly graphical interface with several manipulable input variables to correlate different aspects of tumor growth. By refining model parameters we highlight the significance of heterogeneous intercellular interactions on tumor progression. Within this paper we present the implementation of the Cellular Potts Model graphically presented through Cytoscape.js within a Web application. The tool is available under the MIT license at https://github.com/davcem/cpm-cytoscape and http://styx.cgv.tugraz.at:8080/cpm-cytoscape/ . In-silico methods overcome the lack of wet experimental possibilities and as dry method succeed in terms of reduction, refinement and replacement of animal experimentation, also known as the 3R principles. Our visualization approach to simulation allows for more flexible usage and easy extension to facilitate understanding and gain novel insight. We believe that biomedical research in general and research on tumor growth in particular will benefit from the systems biology perspective.
John T. Perren; Michael Kane; Dehai Zhao; Richard Daniels
2016-01-01
Thinning is a well understood concept used to manage density dependent factors at the standÂ level. This study evaluates the effect of planting density, cultural intensity, and thinning treatment on loblollyÂ pine post-thinning individual tree development. The Lower Coastal Plain Culture/Density Study, has four initialÂ densities, in combination with two cultural...
Modelling the growth of a methanotrophic biofilm
DEFF Research Database (Denmark)
Arcangeli, J.-P.; Arvin, E.
1999-01-01
This article discusses the growth of methanotrophic biofilms. Several independent biofilm growths scenarios involving different inocula were examined. Biofilm growth, substrate removal and product formation were monitored throughout the experiments. Based on the oxygen consumption it was concluded...... that heterotrophs and nitrifiers co-existed with methanotrophs in the biofilm. Heterotrophic biomass grew on soluble polymers formed by the hydrolysis of dead biomass entrapped in the biofilm. Nitrifier populations developed because of the presence of ammonia in the mineral medium. Based on these experimental...... was performed on this model. It indicated that the most influential parameters were those related to the biofilm (i.e. density; solid-volume fraction; thickness). This suggests that in order to improve the model, further research regarding the biofilm structure and composition is needed....
Modeling Fish Growth in Low Dissolved Oxygen
Neilan, Rachael Miller
2013-01-01
This article describes a computational project designed for undergraduate students as an introduction to mathematical modeling. Students use an ordinary differential equation to describe fish weight and assume the instantaneous growth rate depends on the concentration of dissolved oxygen. Published laboratory experiments suggest that continuous…
Stochastic Growth Models with No Discounting
Czech Academy of Sciences Publication Activity Database
Sladký, Karel
2007-01-01
Roč. 15, č. 4 (2007), s. 88-98 ISSN 0572-3043 R&D Projects: GA ČR(CZ) GA402/06/0990; GA ČR GA402/05/0115 Institutional research plan: CEZ:AV0Z10750506 Keywords : economic dynamics * stochastic version of the Ramsey growth model * Markov decision processes Subject RIV: AH - Economics
Vastaranta, Mikko; Kankare, Ville; Holopainen, Markus; Yu, Xiaowei; Hyyppä, Juha; Hyyppä, Hannu
2012-01-01
The two main approaches to deriving forest variables from laser-scanning data are the statistical area-based approach (ABA) and individual tree detection (ITD). With ITD it is feasible to acquire single tree information, as in field measurements. Here, ITD was used for measuring training data for the ABA. In addition to automatic ITD (ITD auto), we tested a combination of ITD auto and visual interpretation (ITD visual). ITD visual had two stages: in the first, ITD auto was carried out and in the second, the results of the ITD auto were visually corrected by interpreting three-dimensional laser point clouds. The field data comprised 509 circular plots ( r = 10 m) that were divided equally for testing and training. ITD-derived forest variables were used for training the ABA and the accuracies of the k-most similar neighbor ( k-MSN) imputations were evaluated and compared with the ABA trained with traditional measurements. The root-mean-squared error (RMSE) in the mean volume was 24.8%, 25.9%, and 27.2% with the ABA trained with field measurements, ITD auto, and ITD visual, respectively. When ITD methods were applied in acquiring training data, the mean volume, basal area, and basal area-weighted mean diameter were underestimated in the ABA by 2.7-9.2%. This project constituted a pilot study for using ITD measurements as training data for the ABA. Further studies are needed to reduce the bias and to determine the accuracy obtained in imputation of species-specific variables. The method could be applied in areas with sparse road networks or when the costs of fieldwork must be minimized.
Mathematical foundations of the dendritic growth models.
Villacorta, José A; Castro, Jorge; Negredo, Pilar; Avendaño, Carlos
2007-11-01
At present two growth models describe successfully the distribution of size and topological complexity in populations of dendritic trees with considerable accuracy and simplicity, the BE model (Van Pelt et al. in J. Comp. Neurol. 387:325-340, 1997) and the S model (Van Pelt and Verwer in Bull. Math. Biol. 48:197-211, 1986). This paper discusses the mathematical basis of these models and analyzes quantitatively the relationship between the BE model and the S model assumed in the literature by developing a new explicit equation describing the BES model (a dendritic growth model integrating the features of both preceding models; Van Pelt et al. in J. Comp. Neurol. 387:325-340, 1997). In numerous studies it is implicitly presupposed that the S model is conditionally linked to the BE model (Granato and Van Pelt in Brain Res. Dev. Brain Res. 142:223-227, 2003; Uylings and Van Pelt in Network 13:397-414, 2002; Van Pelt, Dityatev and Uylings in J. Comp. Neurol. 387:325-340, 1997; Van Pelt and Schierwagen in Math. Biosci. 188:147-155, 2004; Van Pelt and Uylings in Network. 13:261-281, 2002; Van Pelt, Van Ooyen and Uylings in Modeling Dendritic Geometry and the Development of Nerve Connections, pp 179, 2000). In this paper we prove the non-exactness of this assumption, quantify involved errors and determine the conditions under which the BE and S models can be separately used instead of the BES model, which is more exact but considerably more difficult to apply. This study leads to a novel expression describing the BE model in an analytical closed form, much more efficient than the traditional iterative equation (Van Pelt et al. in J. Comp. Neurol. 387:325-340, 1997) in many neuronal classes. Finally we propose a new algorithm in order to obtain the values of the parameters of the BE model when this growth model is matched to experimental data, and discuss its advantages and improvements over the more commonly used procedures.
Modeling error distributions of growth curve models through Bayesian methods.
Zhang, Zhiyong
2016-06-01
Growth curve models are widely used in social and behavioral sciences. However, typical growth curve models often assume that the errors are normally distributed although non-normal data may be even more common than normal data. In order to avoid possible statistical inference problems in blindly assuming normality, a general Bayesian framework is proposed to flexibly model normal and non-normal data through the explicit specification of the error distributions. A simulation study shows when the distribution of the error is correctly specified, one can avoid the loss in the efficiency of standard error estimates. A real example on the analysis of mathematical ability growth data from the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99 is used to show the application of the proposed methods. Instructions and code on how to conduct growth curve analysis with both normal and non-normal error distributions using the the MCMC procedure of SAS are provided.
Integrated Intelligent Modeling, Design and Control of Crystal Growth Processes
National Research Council Canada - National Science Library
Prasad, V
2000-01-01
.... This MURI program took an integrated approach towards modeling, design and control of crystal growth processes and in conjunction with growth and characterization experiments developed much better...
Wang, Y.; Wei, A.; del Campo, A.; Li, Q.; Giles-Hansen, K.
2017-12-01
Large-scale disturbances in Canadian forests, including mountain pine beetle infestation in western Canada, forest fires, timber harvesting and climate change impacts, have significantly affected both forest carbon and water cycles. Thinning, which selectively removes trees at a given forest stand, may be an effective tool to mitigate the effect of these disturbances. Various studies have been conducted to assess the thinning effect on growth, transpiration, and nutrient availability; however, relatively few studies have been conducted to examine its effect on the coupling of forest carbon and water. Thus, the objective of this research is to evaluate the effect of thinning on forest carbon and water coupling at both the leaf and tree levels in a 16-year-old natural Pinus Contorta forest in the interior of British Columbia in Canada. We used water-use efficiency (WUE), the ratio of basal area increment (BA) to tree transpiration (E), as the indicator of the carbon and water coupling at individual tree level, and use intrinsic water-use efficiency (iWUE), the ratio of photosynthesis (A) to stomatal conductance (G), to represent the coupling at the leaf level. Field experiments were conducted in the Upper Penticton Watershed where the mean annual precipitation is 750 mm with seasonal drought during summer. A randomized block design was used, with three blocks each containing two thinning intensities and one unthinned plot (T1: 4,500, T2: 1,100, C: 26,400 trees per ha.). From May to October 2016, basal diameter, sap flow, and environmental conditions were monitored continuously at every 20 minutes, while A and G were measured weekly. Preliminary results showed that thinning significantly increased solar radiation, wind speed, and soil moisture in the treatment plots, where the changes observed were proportional to the intensity of the thinning; but thinning did not change stand level temperature and relative humidity. Thinning also significantly enhanced tree E and BA
Energy Technology Data Exchange (ETDEWEB)
Chadoeuf, J.; Joannes, H.; Nandris, D.; Pierrat, J.C.
1988-12-01
The spread of root diseases in rubber tree (Hevea brasiliensis) due to Rigidoporus lignosus and Phellinus noxius was investigated epidemiologically using data collected every 6 month during a 6-year survey in a plantation. The aim of the present study is to see what factors could predict whether a given tree would be infested at the following inspection. Using a qualitative regression method we expressed the probability of pathogenic attack on a tree in terms of three factors: the state of health of the surrounding trees, the method used to clear the forest prior to planting, and evolution with time. The effects of each factor were ranked, and the roles of the various classes of neighbors were established and quantified. Variability between successive inspections was small, and the method of forest clearing was important only while primary inocula in the soil were still infectious. The state of health of the immediate neighbors was most significant; more distant neighbors in the same row had some effect; interrow spread was extremely rare. This investigation dealt only with trees as individuals, and further study of the interrelationships of groups of trees is needed.
Growth models and analysis of development
Energy Technology Data Exchange (ETDEWEB)
Mathur, G
1979-10-01
This paper deals with remnants of neoclassical elements in Keynesian and post-Keynesian thought, and attempts to demonstrate that the elimination of these elements from our modes of thinking would not impoverish economic analysis as a means of solving real problems. In the Keynesian analysis the causation from investment to savings is exhibited in terms of income determination. When put in terms of a capital-theory model, the vector of savings is represented in two ways: real savings and counterpart real savings. The former coincides with the investment vector and the latter with the vector of consumption goods foregone for diverting resources towards equipment making. Thus the Keynesian causation in capital theory terms makes the concept of national savings as an independent variable redudant. The Robinsonian causation in a golden age with full employment and its reversal of direction in a steady state with non-employment are then considered. But in each of these, variables like rate of savings and output/capital ratio are found to be dormant variables. They are termed as null variables which, being of no account in both full-employment and unemployment situations, could, without loss, be deleted from the repertory of analytical tools. The Harrod formula of warranted rate of growth, when put in causal form, thus becomes a redundant portion of economics of growth. The real determinants of the growth rate and real wage rate on which the analysis of growth or of development should be based, are also depicted.
Modeling and control of greenhouse crop growth
Rodríguez, Francisco; Guzmán, José Luis; Ramírez-Arias, Armando
2015-01-01
A discussion of challenges related to the modeling and control of greenhouse crop growth, this book presents state-of-the-art answers to those challenges. The authors model the subsystems involved in successful greenhouse control using different techniques and show how the models obtained can be exploited for simulation or control design; they suggest ideas for the development of physical and/or black-box models for this purpose. Strategies for the control of climate- and irrigation-related variables are brought forward. The uses of PID control and feedforward compensators, both widely used in commercial tools, are summarized. The benefits of advanced control techniques—event-based, robust, and predictive control, for example—are used to improve on the performance of those basic methods. A hierarchical control architecture is developed governed by a high-level multiobjective optimization approach rather than traditional constrained optimization and artificial intelligence techniques. Reference trajector...
Transitions in a probabilistic interface growth model
International Nuclear Information System (INIS)
Alves, S G; Moreira, J G
2011-01-01
We study a generalization of the Wolf–Villain (WV) interface growth model based on a probabilistic growth rule. In the WV model, particles are randomly deposited onto a substrate and subsequently move to a position nearby where the binding is strongest. We introduce a growth probability which is proportional to a power of the number n i of bindings of the site i: p i ∝n i ν . Through extensive simulations, in (1 + 1) dimensions, we find three behaviors depending on the ν value: (i) if ν is small, a crossover from the Mullins–Herring to the Edwards–Wilkinson (EW) universality class; (ii) for intermediate values of ν, a crossover from the EW to the Kardar–Parisi–Zhang (KPZ) universality class; and, finally, (iii) for large ν values, the system is always in the KPZ class. In (2 + 1) dimensions, we obtain three different behaviors: (i) a crossover from the Villain–Lai–Das Sarma to the EW universality class for small ν values; (ii) the EW class is always present for intermediate ν values; and (iii) a deviation from the EW class is observed for large ν values
Modeling of multibranched crosslike crack growth
International Nuclear Information System (INIS)
Canessa, E.; Tanatar, B.
1991-06-01
Multibranched crosslike crack patterns formed in concentrically loaded square plates are studied in terms of fractal geometry, where the associated fractal dimension d f is calculated for their characterization. We apply simplest deterministic and stochastic approaches at a phenomenological level in an attempt to find generic features as guidelines for future experimental and theoretical work. The deterministic model for fracture propagation we apply, which is a variant of the discretized Laplace approach for randomly ramified fractal cracks proposed by Takayasu, reproduces the basic ingredients of observed complex fracture patters. The stochastic model, although is not strictly a model for crack propagation, is based on diffusion-limited aggregation (DLA) for fractal growth and produces slightly more realistic assessment of the crosslike growth of the cracks in asymmetric multibranches. Nevertheless, this simple ad-hoc DLA-version for modeling the present phenomena as well as the deterministic approach for fracture propagation give fractal dimensionality for the fracture pattern in accord with our estimations made from recent experimental data. It is found that there is a crossover of two fractal dimensions, corresponding to the core (higher d f ) and multibranched crosslike (lower D f ) regions, that contains loops, that are interpreted as representing different symmetry regions within the square plates of finite size. (author). 26 refs, 5 figs
Fang, F. J.
2017-12-01
Reconciling observations at fundamentally different scales is central in understanding the global carbon cycle. This study investigates a model-based melding of forest inventory data, remote-sensing data and micrometeorological-station data ("flux towers" estimating forest heat, CO2 and H2O fluxes). The individual tree-based model FORCCHN was used to evaluate the tree DBH increment and forest carbon fluxes. These are the first simultaneous simulations of the forest carbon budgets from flux towers and individual-tree growth estimates of forest carbon budgets using the continuous forest inventory data — under circumstances in which both predictions can be tested. Along with the global implications of such findings, this also improves the capacity for forest sustainable management and the comprehensive understanding of forest ecosystems. In forest ecology, diameter at breast height (DBH) of a tree significantly determines an individual tree's cross-sectional sapwood area, its biomass and carbon storage. Evaluation the annual DBH increment (ΔDBH) of an individual tree is central to understanding tree growth and forest ecology. Ecosystem Carbon flux is a consequence of key ecosystem processes in the forest-ecosystem carbon cycle, Gross and Net Primary Production (GPP and NPP, respectively) and Net Ecosystem Respiration (NEP). All of these closely relate with tree DBH changes and tree death. Despite advances in evaluating forest carbon fluxes with flux towers and forest inventories for individual tree ΔDBH, few current ecological models can simultaneously quantify and predict the tree ΔDBH and forest carbon flux.
Flower Power: Sunflowers as a Model for Logistic Growth
Fernandez, Eileen; Geist, Kristi A.
2011-01-01
Logistic growth displays an interesting pattern: It starts fast, exhibiting the rapid growth characteristic of exponential models. As time passes, it slows in response to constraints such as limited resources or reallocation of energy. The growth continues to slow until it reaches a limit, called capacity. When the growth describes a population,…
Forest disturbance spurs growth of modeling and technology
Bohrer, G.; Matheny, A. M.; Mirfenderesgi, G.; Morin, T. H.; Rey Sanchez, A. C.; Gough, C. M.; Vogel, C. S.; Nadelhoffer, K. J.; Curtis, P.
2016-12-01
As new opportunities for scientific exploration open, needs for data generate a drive for innovative developments of new research tools. The Forest Accelerated Succession ExperimenT (FASET) was enacted in 2007, continuous flux observations at the University of Michigan Biological Station (UMBS) since 2000. FASET is a large-scale ecological experiment testing the immediate and intermediate term effects of disturbance, and eventually, the role of succession and community composition on forest flux dynamics. Decades-long tree-level observations in the UMBS forest, combined with the long term flux observations allowed us to match the bottom-up accumulated response of individual trees with the top-down whole-plot response measured from the flux tower. However, data describing tree-level canopy structure and hydrological response over an entire plot were not readily available. Unintentionally, FASET became both a motivation and a test-bed for new research tools and approaches. We expanded the operation and analysis approach for a portable canopy LiDARfor 3-D measurements meter-scale canopy structure. We matched canopy LiDAR measurements with root measurements from ground penetrating radar. To study the hydrological effects of the disturbance, we instrumented a large number of trees with Granier-style sap flux sensors. We further developed an approach to use frequency domain reflectometry sensors for continuous measurements of tree water content. We developed an approach to combine plot census, allometry and sap-flux observations in a bottom-up fashion to compare with plot-level EC transpiration rates. We found that while the transpirational water demand in the disturbance plot increased, overall evapotranspiration decreased. This decrease, however, is not uniform across species. A new individual-plant to ecosystem scale hydrodynamic model (FETCH2) demonstrates how specific traits translate to intra-daily differences in plot-level transpiration dynamics.
REFERENCE MODELS OF ENDOGENOUS ECONOMIC GROWTH
GEAMĂNU MARINELA
2012-01-01
The new endogenous growth theories are a very important research area for shaping the most effective policies and long term sustainable development strategies. Endogenous growth theory has emerged as a reaction to the imperfections of neoclassical theory, by the fact that the economic growth is the endogenous product of an economical system.
Modeling urban growth in Kigali city Rwanda
Nduwayezu, G.; Sliuzas, R.V.; Kuffer, M.
2017-01-01
The uncontrolled urban growth is the key characteristics in most cities in less developed countries. However, having a good understanding of the key drivers of the city's growth dynamism has proven to be a key instrument to manage urban growth. This paper investigates the main determinants of Kigali
Study of growth kinetic and modeling of ethanol production by ...
African Journals Online (AJOL)
... coefficient (0.96299). Based on Leudking-Piret model, it could be concluded that ethanol batch fermentation is a non-growth associated process. Key words: Kinetic parameters, simulation, cell growth, ethanol, Saccharomyces cerevisiae.
Reactive burn models and ignition & growth concept
Directory of Open Access Journals (Sweden)
Shaw M.S.
2011-01-01
Full Text Available Plastic-bonded explosives are heterogeneous materials. Experimentally, shock initiation is sensitive to small amounts of porosity, due to the formation of hot spots (small localized regions of high temperature. This leads to the Ignition & Growth concept, introduced by LeeTarver in 1980, as the basis for reactive burn models. A homo- genized burn rate needs to account for three meso-scale physical effects: (i the density of active hot spots or burn centers; (ii the growth of the burn fronts triggered by the burn centers; (iii a geometric factor that accounts for the overlap of deflagration wavelets from adjacent burn centers. These effects can be combined and the burn model defined by specifying the reaction progress variable λ = g(s as a function of a dimensionless reaction length s(t = rbc/ℓbc, rather than by specifying an explicit burn rate. The length scale ℓbc(Ps = [Nbc(Ps]−1/3 is the average distance between burn centers, where Nbc is the number density of burn centers activated by the lead shock. The reaction length rbc(t = ∫t0 D(P(t′dt′ is the distance the burn front propagates from a single burn center, where D(P is the deflagration speed as a function of the local pressure and t is the time since the shock arrival. A key implementation issue is how to determine the lead shock strength in conjunction with a shock capturing scheme. We have developed a robust algorithm for this purpose based on the Hugoniot jump condition for the energy. The algorithm utilizes the time dependence of density, pressure and energy within each cell. The method is independent of the numerical dissipation used for shock capturing. It is local and can be used in one or more space dimensions. The burn model has a small number of parameters which can be calibrated to fit velocity gauge data from shock initiation experiments.
Stochastic modeling of thermal fatigue crack growth
Radu, Vasile
2015-01-01
The book describes a systematic stochastic modeling approach for assessing thermal-fatigue crack-growth in mixing tees, based on the power spectral density of temperature fluctuation at the inner pipe surface. It shows the development of a frequency-temperature response function in the framework of single-input, single-output (SISO) methodology from random noise/signal theory under sinusoidal input. The frequency response of stress intensity factor (SIF) is obtained by a polynomial fitting procedure of thermal stress profiles at various instants of time. The method, which takes into account the variability of material properties, and has been implemented in a real-world application, estimates the probabilities of failure by considering a limit state function and Monte Carlo analysis, which are based on the proposed stochastic model. Written in a comprehensive and accessible style, this book presents a new and effective method for assessing thermal fatigue crack, and it is intended as a concise and practice-or...
Neo-logistic model for the growth of bacteria
Tashiro, Tohru; Yoshimura, Fujiko
2017-01-01
We propose a neo-logistic model that can describe bacterial growth data precisely. This model is not derived by modifying the logistic model formally, but by incorporating the synthesis of inducible enzymes into the logistic model indirectly. Therefore, the meaning of the parameters of the neo-logistic model becomes physically clear. The neo-logistic model can approximate bacterial growth better than models previously presented, and predict the order of the saturated number of bacteria in the...
Testing linear growth rate formulas of non-scale endogenous growth models
Ziesemer, Thomas
2017-01-01
Endogenous growth theory has produced formulas for steady-state growth rates of income per capita which are linear in the growth rate of the population. Depending on the details of the models, slopes and intercepts are positive, zero or negative. Empirical tests have taken over the assumption of
A literature review on growth models and strategies: The missing link in entrepreneurial growth
Directory of Open Access Journals (Sweden)
Syed Fida Hussain Shah
2013-08-01
Full Text Available This study focuses on the importance of growth models, growth strategies, role of knowledge management system in the formulation of effective strategy for the enterprises following growth. Choice of an appropriate growth strategy is at the heart of any successful entrepreneurial venture. Selection of a strategy may be effective for one entrepreneur while it is not for other. Choice of Growth Strategy depends on various different factors, organisational context and environment which may vary from enterprise to enterprise. Resource based view is very important consideration for the entrepreneurs on the path of growth. Evaluation of all kind of resources helps them to grow their enterprises successfully. Selection of an appropriate growth strategy allows the entrepreneurs in overcoming growth challenges and avoiding the growth reversals and setbacks.
Layered growth model and epitaxial growth structures for SiCAlN alloys
International Nuclear Information System (INIS)
Liu Zhaoqing; Ni Jun; Su Xiaoao; Dai Zhenhong
2009-01-01
Epitaxial growth structures for (SiC) 1-x (AlN) x alloys are studied using a layered growth model. First-principle calculations are used to determine the parameters in the layered growth model. The phase diagrams of epitaxial growth are given. There is a rich variety of the new metastable polytype structures at x=1/6 ,1/5 ,1/4 ,1/3 , and 1/2 in the layered growth phase diagrams. We have also calculated the electronic properties of the short periodical SiCAlN alloys predicted by our layered growth model. The results show that various ordered structures of (SiC) 1-x (AlN) x alloys with the band gaps over a wide range are possible to be synthesized by epitaxial growth.
Evaluating growth assumptions using diameter or radial increments in natural even-aged longleaf pine
John C. Gilbert; Ralph S. Meldahl; Jyoti N. Rayamajhi; John S. Kush
2010-01-01
When using increment cores to predict future growth, one often assumes future growth is identical to past growth for individual trees. Once this assumption is accepted, a decision has to be made between which growth estimate should be used, constant diameter growth or constant basal area growth. Often, the assumption of constant diameter growth is used due to the ease...
Forest Growth and Yield Models Viewed From a Different Perspective
Jeffery C. Goelz
2002-01-01
Typically, when different forms of growth and yield models are considered, they are grouped into convenient discrete classes. As a heuristic device, I chose to use a contrasting perspective, that all growth and yield models are diameter distribution models that merely differ in regard to which diameter distribution is employed and how the distribution is projected to...
Parameter Estimates in Differential Equation Models for Population Growth
Winkel, Brian J.
2011-01-01
We estimate the parameters present in several differential equation models of population growth, specifically logistic growth models and two-species competition models. We discuss student-evolved strategies and offer "Mathematica" code for a gradient search approach. We use historical (1930s) data from microbial studies of the Russian biologist,…
Spiral Growth in Plants: Models and Simulations
Allen, Bradford D.
2004-01-01
The analysis and simulation of spiral growth in plants integrates algebra and trigonometry in a botanical setting. When the ideas presented here are used in a mathematics classroom/computer lab, students can better understand how basic assumptions about plant growth lead to the golden ratio and how the use of circular functions leads to accurate…
Growth Kinetics and Modeling of Direct Oxynitride Growth with NO-O2 Gas Mixtures
Energy Technology Data Exchange (ETDEWEB)
Everist, Sarah; Nelson, Jerry; Sharangpani, Rahul; Smith, Paul Martin; Tay, Sing-Pin; Thakur, Randhir
1999-05-03
We have modeled growth kinetics of oxynitrides grown in NO-O_{2} gas mixtures from first principles using modified Deal-Grove equations. Retardation of oxygen diffusion through the nitrided dielectric was assumed to be the dominant growth-limiting step. The model was validated against experimentally obtained curves with good agreement. Excellent uniformity, which exceeded expected walues, was observed.
Detecting Growth Shape Misspecifications in Latent Growth Models: An Evaluation of Fit Indexes
Leite, Walter L.; Stapleton, Laura M.
2011-01-01
In this study, the authors compared the likelihood ratio test and fit indexes for detection of misspecifications of growth shape in latent growth models through a simulation study and a graphical analysis. They found that the likelihood ratio test, MFI, and root mean square error of approximation performed best for detecting model misspecification…
Modeling Urban Spatial Growth in Mountainous Regions of Western China
Directory of Open Access Journals (Sweden)
Guoping Huang
2017-08-01
Full Text Available The scale and speed of urbanization in the mountainous regions of western China have received little attention from researchers. These cities are facing rapid population growth and severe environmental degradation. This study analyzed historical urban growth trends in this mountainous region to better understand the interaction between the spatial growth pattern and the mountainous topography. Three major factors—slope, accessibility, and land use type—were studied in light of their relationships with urban spatial growth. With the analysis of historical data as the basis, a conceptual urban spatial growth model was devised. In this model, slope, accessibility, and land use type together create resistance to urban growth, while accessibility controls the sequence of urban development. The model was tested and evaluated using historical data. It serves as a potential tool for planners to envision and assess future urban growth scenarios and their potential environmental impacts to make informed decisions.
Differential model of macroeconomic growth with endogenic cyclicity
Directory of Open Access Journals (Sweden)
Mikhail I. Geraskin
2017-09-01
Full Text Available Objective to elaborate a mathematical model of economic growth taking into account the cyclical nature of macroeconomic dynamics with the model parameters based on the Russian economy statistics. Methods economic and mathematical modeling system analysis regression factor analysis econometric time series analysis. Results the article states that under unstable economic growth in Russia forecasting of strategic prospects of the Russian economy is one of the topical directions of scientific studies. Furthermore construction of predictive models should be based on multiple factors taking into account such basic concepts as the neoKeynesian HarrodDomar model Ramsey ndash Cass ndash Koopmans model S. V. Dubovskiyrsquos concept as well as the neoclassical growth model by R. Solow. They served as the basis for developing a multifactor differential economic growth model which is a modification of the neoclassical growth model by R. Solow taking into account the laborsaving and capitalsaving forms of scientifictechnical progress and the Keynesian concept of investment. The model parameters are determined based on the dynamics of actual GDP employment fixed assets and investments in fixed assets for 19652016 in Russia on the basis of official statistics. The generalized model showed the presence of longwave fluctuations that are not detected during the individual periods modeling. The cyclical nature of macroeconomic dynamics with a period of 54 years was found which corresponds to the parameters of long waves by N. D. Kondratiev. Basing on the model the macroeconomic growth forecast was generated which shows that after 2020 the increase of scientifictechnical progress will be negative. Scientific novelty a model is proposed of the scientifictechnical progress indicator showing the growth rate of the capital productivity ratio to the saving rate a differential model of macroeconomic growth is obtained which endogenously takes cyclicity into account
Foster, Jane R.; Finley, Andrew O.; D'Amato, Anthony W.; Bradford, John B.; Banerjee, Sudipto
2016-01-01
As global temperatures rise, variation in annual climate is also changing, with unknown consequences for forest biomes. Growing forests have the ability to capture atmospheric CO2and thereby slow rising CO2 concentrations. Forests’ ongoing ability to sequester C depends on how tree communities respond to changes in climate variation. Much of what we know about tree and forest response to climate variation comes from tree-ring records. Yet typical tree-ring datasets and models do not capture the diversity of climate responses that exist within and among trees and species. We address this issue using a model that estimates individual tree response to climate variables while accounting for variation in individuals’ size, age, competitive status, and spatially structured latent covariates. Our model allows for inference about variance within and among species. We quantify how variables influence aboveground biomass growth of individual trees from a representative sample of 15 northern or southern tree species growing in a transition zone between boreal and temperate biomes. Individual trees varied in their growth response to fluctuating mean annual temperature and summer moisture stress. The variation among individuals within a species was wider than mean differences among species. The effects of mean temperature and summer moisture stress interacted, such that warm years produced positive responses to summer moisture availability and cool years produced negative responses. As climate models project significant increases in annual temperatures, growth of species likeAcer saccharum, Quercus rubra, and Picea glauca will vary more in response to summer moisture stress than in the past. The magnitude of biomass growth variation in response to annual climate was 92–95% smaller than responses to tree size and age. This means that measuring or predicting the physical structure of current and future forests could tell us more about future C dynamics than growth
Foster, Jane R; Finley, Andrew O; D'Amato, Anthony W; Bradford, John B; Banerjee, Sudipto
2016-06-01
As global temperatures rise, variation in annual climate is also changing, with unknown consequences for forest biomes. Growing forests have the ability to capture atmospheric CO2 and thereby slow rising CO2 concentrations. Forests' ongoing ability to sequester C depends on how tree communities respond to changes in climate variation. Much of what we know about tree and forest response to climate variation comes from tree-ring records. Yet typical tree-ring datasets and models do not capture the diversity of climate responses that exist within and among trees and species. We address this issue using a model that estimates individual tree response to climate variables while accounting for variation in individuals' size, age, competitive status, and spatially structured latent covariates. Our model allows for inference about variance within and among species. We quantify how variables influence aboveground biomass growth of individual trees from a representative sample of 15 northern or southern tree species growing in a transition zone between boreal and temperate biomes. Individual trees varied in their growth response to fluctuating mean annual temperature and summer moisture stress. The variation among individuals within a species was wider than mean differences among species. The effects of mean temperature and summer moisture stress interacted, such that warm years produced positive responses to summer moisture availability and cool years produced negative responses. As climate models project significant increases in annual temperatures, growth of species like Acer saccharum, Quercus rubra, and Picea glauca will vary more in response to summer moisture stress than in the past. The magnitude of biomass growth variation in response to annual climate was 92-95% smaller than responses to tree size and age. This means that measuring or predicting the physical structure of current and future forests could tell us more about future C dynamics than growth responses
Modeling urban growth in Kigali city Rwanda
African Journals Online (AJOL)
kagoyire
industrialization, land consumption and infrastructural development, have impacted ..... urban growth (reference image) and urban development predicted to the ..... neighboring characteristics (regular water and electricity provision) were not ...
Growth of cortical neuronal network in vitro: Modeling and analysis
International Nuclear Information System (INIS)
Lai, P.-Y.; Jia, L. C.; Chan, C. K.
2006-01-01
We present a detailed analysis and theoretical growth models to account for recent experimental data on the growth of cortical neuronal networks in vitro [Phys. Rev. Lett. 93, 088101 (2004)]. The experimentally observed synchronized firing frequency of a well-connected neuronal network is shown to be proportional to the mean network connectivity. The growth of the network is consistent with the model of an early enhanced growth of connection, but followed by a retarded growth once the synchronized cluster is formed. Microscopic models with dominant excluded volume interactions are consistent with the observed exponential decay of the mean connection probability as a function of the mean network connectivity. The biological implications of the growth model are also discussed
Modeling the effects of ozone on soybean growth and yield.
Kobayashi, K; Miller, J E; Flagler, R B; Heck, W W
1990-01-01
A simple mechanistic model was developed based on an existing growth model in order to address the mechanisms of the effects of ozone on growth and yield of soybean [Glycine max. (L.) Merr. 'Davis'] and interacting effects of other environmental stresses. The model simulates daily growth of soybean plants using environmental data including shortwave radiation, temperature, precipitation, irrigation and ozone concentration. Leaf growth, dry matter accumulation, water budget, nitrogen input and seed growth linked to senescence and abscission of leaves are described in the model. The effects of ozone are modeled as reduced photosynthate production and accelerated senescence. The model was applied to the open-top chamber experiments in which soybean plants were exposed to ozone under two levels of soil moisture regimes. After calibrating the model to the growth data and seed yield, goodness-of-fit of the model was tested. The model fitted well for top dry weight in the vegetative growth phase and also at maturity. The effect of ozone on seen yield was also described satisfactorily by the model. The simulation showed apparent interaction between the effect of ozone and soil moisture stress on the seed yield. The model revealed that further work is needed concerning the effect of ozone on the senescence process and the consequences of alteration of canopy microclimate by the open-top chambers.
Tax Evasion in a Model of Endogenous Growth
Been-Lon Chen
2003-01-01
This paper integrates tax evasion into a standard AK growth model with public capital. In the model, the government optimizes the tax rate, while individuals optimize tax evasion. It studies tax rate, tax evasion and economic growth, and compares them with otherwise identical economies except those without tax evasion. It inquires into the effects of three government policies on tax rate, tax evasion, and economic growth. It finds that an increase in both unit cost of tax evasion and punishme...
Stochastic growth logistic model with aftereffect for batch fermentation process
Rosli, Norhayati; Ayoubi, Tawfiqullah; Bahar, Arifah; Rahman, Haliza Abdul; Salleh, Madihah Md
2014-06-01
In this paper, the stochastic growth logistic model with aftereffect for the cell growth of C. acetobutylicum P262 and Luedeking-Piret equations for solvent production in batch fermentation system is introduced. The parameters values of the mathematical models are estimated via Levenberg-Marquardt optimization method of non-linear least squares. We apply Milstein scheme for solving the stochastic models numerically. The effciency of mathematical models is measured by comparing the simulated result and the experimental data of the microbial growth and solvent production in batch system. Low values of Root Mean-Square Error (RMSE) of stochastic models with aftereffect indicate good fits.
Stochastic growth logistic model with aftereffect for batch fermentation process
International Nuclear Information System (INIS)
Rosli, Norhayati; Ayoubi, Tawfiqullah; Bahar, Arifah; Rahman, Haliza Abdul; Salleh, Madihah Md
2014-01-01
In this paper, the stochastic growth logistic model with aftereffect for the cell growth of C. acetobutylicum P262 and Luedeking-Piret equations for solvent production in batch fermentation system is introduced. The parameters values of the mathematical models are estimated via Levenberg-Marquardt optimization method of non-linear least squares. We apply Milstein scheme for solving the stochastic models numerically. The effciency of mathematical models is measured by comparing the simulated result and the experimental data of the microbial growth and solvent production in batch system. Low values of Root Mean-Square Error (RMSE) of stochastic models with aftereffect indicate good fits
Stochastic growth logistic model with aftereffect for batch fermentation process
Energy Technology Data Exchange (ETDEWEB)
Rosli, Norhayati; Ayoubi, Tawfiqullah [Faculty of Industrial Sciences and Technology, Universiti Malaysia Pahang, Lebuhraya Tun Razak, 26300 Gambang, Pahang (Malaysia); Bahar, Arifah; Rahman, Haliza Abdul [Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia); Salleh, Madihah Md [Department of Biotechnology Industry, Faculty of Biosciences and Bioengineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia)
2014-06-19
In this paper, the stochastic growth logistic model with aftereffect for the cell growth of C. acetobutylicum P262 and Luedeking-Piret equations for solvent production in batch fermentation system is introduced. The parameters values of the mathematical models are estimated via Levenberg-Marquardt optimization method of non-linear least squares. We apply Milstein scheme for solving the stochastic models numerically. The effciency of mathematical models is measured by comparing the simulated result and the experimental data of the microbial growth and solvent production in batch system. Low values of Root Mean-Square Error (RMSE) of stochastic models with aftereffect indicate good fits.
Testing R&D-Based Endogenous Growth Models
DEFF Research Database (Denmark)
Kruse-Andersen, Peter Kjær
2017-01-01
R&D-based growth models are tested using US data for the period 1953-2014. A general growth model is developed which nests the model varieties of interest. The model implies a cointegrating relationship between multifactor productivity, research intensity, and employment. This relationship...... is estimated using cointegrated VAR models. The results provide evidence against the widely used fully endogenous variety and in favor of the semi-endogenous variety. Forecasts based on the empirical estimates suggest that the slowdown in US productivity growth will continue. Particularly, the annual long...
Kinetic models of cell growth, substrate utilization and bio ...
African Journals Online (AJOL)
STORAGESEVER
2008-05-02
May 2, 2008 ... Aspergillus fumigatus. A simple model was proposed using the Logistic Equation for the growth, ... costs and also involved in less sophisticated fermentation ... apply and they are accurately proved that the model can express ...
Nonlinear Growth Models in M"plus" and SAS
Grimm, Kevin J.; Ram, Nilam
2009-01-01
Nonlinear growth curves or growth curves that follow a specified nonlinear function in time enable researchers to model complex developmental patterns with parameters that are easily interpretable. In this article we describe how a variety of sigmoid curves can be fit using the M"plus" structural modeling program and the nonlinear…
Growth rate in the dynamical dark energy models
International Nuclear Information System (INIS)
Avsajanishvili, Olga; Arkhipova, Natalia A.; Samushia, Lado; Kahniashvili, Tina
2014-01-01
Dark energy models with a slowly rolling cosmological scalar field provide a popular alternative to the standard, time-independent cosmological constant model. We study the simultaneous evolution of background expansion and growth in the scalar field model with the Ratra-Peebles self-interaction potential. We use recent measurements of the linear growth rate and the baryon acoustic oscillation peak positions to constrain the model parameter α that describes the steepness of the scalar field potential. (orig.)
Growth rate in the dynamical dark energy models.
Avsajanishvili, Olga; Arkhipova, Natalia A; Samushia, Lado; Kahniashvili, Tina
Dark energy models with a slowly rolling cosmological scalar field provide a popular alternative to the standard, time-independent cosmological constant model. We study the simultaneous evolution of background expansion and growth in the scalar field model with the Ratra-Peebles self-interaction potential. We use recent measurements of the linear growth rate and the baryon acoustic oscillation peak positions to constrain the model parameter [Formula: see text] that describes the steepness of the scalar field potential.
Bar-El Dadon, Shimrit; Shahar, Ron; Katalan, Vered; Monsonego-Ornan, Efrat; Reifen, Ram
2011-09-01
Skeletal abnormalities are one of the hallmarks of growth delay during gestation. The aim of this study was to determine changes induced by leptin in skeletal growth and development in a rat model of intrauterine growth retardation (IUGR) and to elucidate the possible underlying mechanisms. Intrauterine growth retardation was induced prepartum and the effects of leptin to mothers prenatally or to offspring postnatally were studied. Radii were harvested and tested mechanically and structurally. Tibias were evaluated for growth-plate morphometry. On day 40 postpartum, total bone length and mineral density and tibial growth-plate width and numbers of cells within its zones of offspring treated with leptin were significantly greater than in the control group. Postnatal leptin administration in an IUGR model improves the structural properties and elongation rate of bone. These findings could pave the way to preventing some phenotypic presentations of IUGR. Copyright © 2011 Elsevier Inc. All rights reserved.
Graphene growth process modeling: a physical-statistical approach
Wu, Jian; Huang, Qiang
2014-09-01
As a zero-band semiconductor, graphene is an attractive material for a wide variety of applications such as optoelectronics. Among various techniques developed for graphene synthesis, chemical vapor deposition on copper foils shows high potential for producing few-layer and large-area graphene. Since fabrication of high-quality graphene sheets requires the understanding of growth mechanisms, and methods of characterization and control of grain size of graphene flakes, analytical modeling of graphene growth process is therefore essential for controlled fabrication. The graphene growth process starts with randomly nucleated islands that gradually develop into complex shapes, grow in size, and eventually connect together to cover the copper foil. To model this complex process, we develop a physical-statistical approach under the assumption of self-similarity during graphene growth. The growth kinetics is uncovered by separating island shapes from area growth rate. We propose to characterize the area growth velocity using a confined exponential model, which not only has clear physical explanation, but also fits the real data well. For the shape modeling, we develop a parametric shape model which can be well explained by the angular-dependent growth rate. This work can provide useful information for the control and optimization of graphene growth process on Cu foil.
Mechanical model for filament buckling and growth by phase ordering.
Rey, Alejandro D; Abukhdeir, Nasser M
2008-02-05
A mechanical model of open filament shape and growth driven by phase ordering is formulated. For a given phase-ordering driving force, the model output is the filament shape evolution and the filament end-point kinematics. The linearized model for the slope of the filament is the Cahn-Hilliard model of spinodal decomposition, where the buckling corresponds to concentration fluctuations. Two modes are predicted: (i) sequential growth and buckling and (ii) simultaneous buckling and growth. The relation among the maximum buckling rate, filament tension, and matrix viscosity is given. These results contribute to ongoing work in smectic A filament buckling.
Modeling and optimization of algae growth
Thornton, Anthony Richard; Weinhart, Thomas; Bokhove, Onno; Zhang, Bowen; van der Sar, Dick M.; Kumar, Kundan; Pisarenco, Maxim; Rudnaya, Maria; Savcenco, Valeriu; Rademacher, Jens; Zijlstra, Julia; Szabelska, Alicja; Zyprych, Joanna; van der Schans, Martin; Timperio, Vincent; Veerman, Frits
2010-01-01
The wastewater from greenhouses has a high amount of mineral contamination and an environmentally-friendly method of removal is to use algae to clean this runoff water. The algae consume the minerals as part of their growth process. In addition to cleaning the water, the created algal bio-mass has a
Optimal Patent Life in a Variety-Expansion Growth Model
Lin, Hwan C.
2013-01-01
This paper presents more channels through which the optimal patent life is determined in a R&D-based endogenous growth model that permits growth of new varieties of consumer goods over time. Its modeling features include an endogenous hazard rate facing incumbent monopolists, the prevalence of research congestion, and the aggregate welfare importance of product differentiation. As a result, a patent’s effective life is endogenized and less than its legal life. The model is calibrated to a glo...
Modeling of Craniofacial Anatomy, Variation, and Growth
DEFF Research Database (Denmark)
Thorup, Signe Strann
The topic of this thesis is automatic analysis of craniofacial images with respect to changes due to growth and surgery, inter-subject variation and intracranial volume estimation. The methods proposed contribute to the knowledge about specific craniofacial anomalies, as well as provide a tool...... for detailed analyses for clinical and research purposes. Most of the applications in this thesis rely on non-rigid image registration by the means of warping one image into the coordinate system of another image. This warping results in a deformation field that describes the anatomical correspondence between......, thus creating a personalized atlas. The knowledge built into the atlas is e.g. location of anatomical regions and landmarks of importance to surgery planning and evaluation or population studies. With these correspondences, various analyses could be carried out e.g. quantification of growth, inter...
Modelling the Growth of Swine Flu
Thomson, Ian
2010-01-01
The spread of swine flu has been a cause of great concern globally. With no vaccine developed as yet, (at time of writing in July 2009) and given the fact that modern-day humans can travel speedily across the world, there are fears that this disease may spread out of control. The worst-case scenario would be one of unfettered exponential growth.…
On Latent Growth Models for Composites and Their Constituents.
Hancock, Gregory R; Mao, Xiulin; Kher, Hemant
2013-09-01
Over the last decade and a half, latent growth modeling has become an extremely popular and versatile technique for evaluating longitudinal change and its determinants. Most common among the models applied are those for a single measured variable over time. This model has been extended in a variety of ways, most relevant for the current work being the multidomain and the second-order latent growth models. Whereas the former allows for growth function characteristics to be modeled for multiple outcomes simultaneously, with the degree of growth characteristics' relations assessed within the model (e.g., cross-domain slope factor correlations), the latter models growth in latent outcomes, each of which has effect indicators repeated over time. But what if one has an outcome that is believed to be formative relative to its indicator variables rather than latent? In this case, where the outcome is a composite of multiple constituents, modeling change over time is less straightforward. This article provides analytical and applied details for simultaneously modeling growth in composites and their constituent elements, including a real data example using a general computer self-efficacy questionnaire.
Stochastic process corrosion growth models for pipeline reliability
International Nuclear Information System (INIS)
Bazán, Felipe Alexander Vargas; Beck, André Teófilo
2013-01-01
Highlights: •Novel non-linear stochastic process corrosion growth model is proposed. •Corrosion rate modeled as random Poisson pulses. •Time to corrosion initiation and inherent time-variability properly represented. •Continuous corrosion growth histories obtained. •Model is shown to precisely fit actual corrosion data at two time points. -- Abstract: Linear random variable corrosion models are extensively employed in reliability analysis of pipelines. However, linear models grossly neglect well-known characteristics of the corrosion process. Herein, a non-linear model is proposed, where corrosion rate is represented as a Poisson square wave process. The resulting model represents inherent time-variability of corrosion growth, produces continuous growth and leads to mean growth at less-than-one power of time. Different corrosion models are adjusted to the same set of actual corrosion data for two inspections. The proposed non-linear random process corrosion growth model leads to the best fit to the data, while better representing problem physics
Directory of Open Access Journals (Sweden)
Dejun Yang
Full Text Available ABSTRACT Simulations for root growth, crop growth, and N uptake in agro-hydrological models are of significant concern to researchers. SWMS_2D is one of the most widely used physical hydrologically related models. This model solves equations that govern soil-water movement by the finite element method, and has a public access source code. Incorporating key agricultural components into the SWMS_2D model is of practical importance, especially for modeling some critical cereal crops such as winter wheat. We added root growth, crop growth, and N uptake modules into SWMS_2D. The root growth model had two sub-models, one for root penetration and the other for root length distribution. The crop growth model used was adapted from EU-ROTATE_N, linked to the N uptake model. Soil-water limitation, nitrogen limitation, and temperature effects were all considered in dry-weight modeling. Field experiments for winter wheat in Bouwing, the Netherlands, in 1983-1984 were selected for validation. Good agreements were achieved between simulations and measurements, including soil water content at different depths, normalized root length distribution, dry weight and nitrogen uptake. This indicated that the proposed new modules used in the SWMS_2D model are robust and reliable. In the future, more rigorous validation should be carried out, ideally under 2D situations, and attention should be paid to improve some modules, including the module simulating soil N mineralization.
Applied model for the growth of the daytime mixed layer
DEFF Research Database (Denmark)
Batchvarova, E.; Gryning, Sven-Erik
1991-01-01
numerically. When the mixed layer is shallow or the atmosphere nearly neutrally stratified, the growth is controlled mainly by mechanical turbulence. When the layer is deep, its growth is controlled mainly by convective turbulence. The model is applied on a data set of the evolution of the height of the mixed...... layer in the morning hours, when both mechanical and convective turbulence contribute to the growth process. Realistic mixed-layer developments are obtained....
Weinberger, J. L.; Quinlan, P. T.; Martin, J.; Tartakovsky, D. M.
2013-12-01
Watershed scale estimates of evapotranspiration (ET) have proven difficult to quantify in areas of native vegetation with uncertain or unknown crop coefficients. In this study, we evaluate the water use in Quercus engelmanni and Quercus agrifolia, two species of oak native to Southern California. Thermal dissipation probes (TDPs) were installed at four locations within a 14,500 acre watershed, comprising 770 acres of Q. agrifolia woodland and 2440 acres of Q. engelmanni woodland. Installation duration ranged from 6 weeks to 14 months. The TDPs were calibrated to each species in the laboratory using limbs ranging from 2 to 5 inches in diameter. Dye was run through each limb at the end of the calibration test in order to establish a relationship between active sapwood area and limb diameter. ET measured in the field for each species was 0.15 to 0.3 times that of the reference evapotranspiration (ETo) derived from the Penman-Monteith equation, with the primary variability in the demand related to measured incident solar radiation. The total water demand for each species is estimated using the laboratory determined relationship between the active sapwood area and the diameter of the limb, and a survey of the tree diameter breast height (DBH) of each tree in the watershed. This study provides new insight into the actual water demand of two native tree species in Southern California and has serious implications for conservation plans, which are often developed using watershed models that apply ETo to all vegetation communities, regardless of actual water demand.
Non-rigid image registration using bone growth model
DEFF Research Database (Denmark)
Bro-Nielsen, Morten; Gramkow, Claus; Kreiborg, Sven
1997-01-01
Non-rigid registration has traditionally used physical models like elasticity and fluids. These models are very seldom valid models of the difference between the registered images. This paper presents a non-rigid registration algorithm, which uses a model of bone growth as a model of the change...... between time sequence images of the human mandible. By being able to register the images, this paper at the same time contributes to the validation of the growth model, which is based on the currently available medical theories and knowledge...
Phase-field model of eutectic growth
International Nuclear Information System (INIS)
Karma, A.
1994-01-01
A phase-field model which describes the solidification of a binary eutectic alloy with a simple symmetric phase diagram is introduced and the sharp-interface limit of this model is explored both analytically and numerically
Balanced growth path solutions of a Boltzmann mean field game model for knowledge growth
Burger, Martin
2016-11-18
In this paper we study balanced growth path solutions of a Boltzmann mean field game model proposed by Lucas and Moll [15] to model knowledge growth in an economy. Agents can either increase their knowledge level by exchanging ideas in learning events or by producing goods with the knowledge they already have. The existence of balanced growth path solutions implies exponential growth of the overall production in time. We prove existence of balanced growth path solutions if the initial distribution of individuals with respect to their knowledge level satisfies a Pareto-tail condition. Furthermore we give first insights into the existence of such solutions if in addition to production and knowledge exchange the knowledge level evolves by geometric Brownian motion.
A smart growth evaluation model based on data envelopment analysis
Zhang, Xiaokun; Guan, Yongyi
2018-04-01
With the rapid spread of urbanization, smart growth (SG) has attracted plenty of attention from all over the world. In this paper, by the establishment of index system for smart growth, data envelopment analysis (DEA) model was suggested to evaluate the SG level of the current growth situation in cities. In order to further improve the information of both radial direction and non-radial detection, we introduced the non-Archimedean infinitesimal to form C2GS2 control model. Finally, we evaluated the SG level in Canberra and identified a series of problems, which can verify the applicability of the model and provide us more improvement information.
Studying historical occupational careers with multilevel growth models
Directory of Open Access Journals (Sweden)
Wiebke Schulz
2010-10-01
Full Text Available In this article we propose to study occupational careers with historical data by using multilevel growth models. Historical career data are often characterized by a lack of information on the timing of occupational changes and by different numbers of observations of occupations per individual. Growth models can handle these specificities, whereas standard methods, such as event history analyses can't. We illustrate the use of growth models by studying career success of men and women, using data from the Historical Sample of the Netherlands. The results show that the method is applicable to male careers, but causes trouble when analyzing female careers.
Modeling growth from weaning to maturity in beef cattle breeds
To better understand growth trajectory and maturity differences between beef breeds, three models – Brody, spline, and quadratic – were fit to cow growth data, and resulting parameter estimates were evaluated for 3 breed categories – British, continental, and Brahman-influenced. The data were weight...
Modeling growth of Clostridium perfringens in pea soup during cooling
Jong, de A.E.I.; Beumer, R.R.; Zwietering, M.H.
2005-01-01
Clostridium perfringens is a pathogen that mainly causes food poisoning outbreaks when large quantities of food are prepared. Therefore, a model was developed to predict the effect of different cooling procedures on the growth of this pathogen during cooling of food: Dutch pea soup. First, a growth
Evaluating the Predictive Value of Growth Prediction Models
Murphy, Daniel L.; Gaertner, Matthew N.
2014-01-01
This study evaluates four growth prediction models--projection, student growth percentile, trajectory, and transition table--commonly used to forecast (and give schools credit for) middle school students' future proficiency. Analyses focused on vertically scaled summative mathematics assessments, and two performance standards conditions (high…
Modelling growth curves of Nigerian indigenous normal feather ...
African Journals Online (AJOL)
This study was conducted to predict the growth curve parameters using Bayesian Gompertz and logistic models and also to compare the two growth function in describing the body weight changes across age in Nigerian indigenous normal feather chicken. Each chick was wing-tagged at day old and body weights were ...
A Schumpeterian Model of Entrepreneurship, Innovation, and Regional Economic Growth
Batabyal, A.; Nijkamp, P.
2012-01-01
The authors provide the first theoretical analysis of a one-sector, discrete-time, Schumpeterian model of growth in a regional economy in which consumers are risk neutral, there is no population growth, monopolistic entrepreneurs produce intermediate goods, and a single consumption good is produced
A grain boundary sliding model for cavitation, crack growth and ...
African Journals Online (AJOL)
A model is presented for cavity growth, crack propagation and fracture resulting from grain boundary sliding (GBS) during high temperature creep deformation. The theory of cavity growth by GBS was based on energy balance criteria on the assumption that the matrix is sufficiently plastic to accommodate misfit strains ...
A size-structured model of bacterial growth and reproduction.
Ellermeyer, S F; Pilyugin, S S
2012-01-01
We consider a size-structured bacterial population model in which the rate of cell growth is both size- and time-dependent and the average per capita reproduction rate is specified as a model parameter. It is shown that the model admits classical solutions. The population-level and distribution-level behaviours of these solutions are then determined in terms of the model parameters. The distribution-level behaviour is found to be different from that found in similar models of bacterial population dynamics. Rather than convergence to a stable size distribution, we find that size distributions repeat in cycles. This phenomenon is observed in similar models only under special assumptions on the functional form of the size-dependent growth rate factor. Our main results are illustrated with examples, and we also provide an introductory study of the bacterial growth in a chemostat within the framework of our model.
Directory of Open Access Journals (Sweden)
Songqiu Deng
2013-12-01
Full Text Available This study attempted to measure forest resources at the individual tree level using high-resolution images by combining GPS, RS, and Geographic Information System (GIS technologies. The images were acquired by the WorldView-2 satellite with a resolution of 0.5 m in the panchromatic band and 2.0 m in the multispectral bands. Field data of 90 plots were used to verify the interpreted accuracy. The tops of trees in three groups, namely ≥10 cm, ≥15 cm, and ≥20 cm DBH (diameter at breast height, were extracted by the individual tree crown (ITC approach using filters with moving windows of 3 × 3 pixels, 5 × 5 pixels and 7 × 7 pixels, respectively. In the study area, there were 1,203,970 trees of DBH over 10 cm, and the interpreted accuracy was 73.68 ± 15.14% averaged over the 90 plots. The numbers of the trees that were ≥15 cm and ≥20 cm DBH were 727,887 and 548,919, with an average accuracy of 68.74 ± 17.21% and 71.92 ± 18.03%, respectively. The pixel-based classification showed that the classified accuracies of the 16 classes obtained using the eight multispectral bands were higher than those obtained using only the four standard bands. The increments ranged from 0.1% for the water class to 17.0% for Metasequoia glyptostroboides, with an average value of 4.8% for the 16 classes. In addition, to overcome the “mixed pixels” problem, a crown-based supervised classification, which can improve the classified accuracy of both dominant species and smaller classes, was used for generating a thematic map of tree species. The improvements of the crown- to pixel-based classification ranged from −1.6% for the open forest class to 34.3% for Metasequoia glyptostroboides, with an average value of 20.3% for the 10 classes. All tree tops were then annotated with the species attributes from the map, and a tree count of different species indicated that the forest of Purple Mountain is mainly dominated by Quercus acutissima, Liquidambar formosana
Selection, calibration, and validation of models of tumor growth.
Lima, E A B F; Oden, J T; Hormuth, D A; Yankeelov, T E; Almeida, R C
2016-11-01
This paper presents general approaches for addressing some of the most important issues in predictive computational oncology concerned with developing classes of predictive models of tumor growth. First, the process of developing mathematical models of vascular tumors evolving in the complex, heterogeneous, macroenvironment of living tissue; second, the selection of the most plausible models among these classes, given relevant observational data; third, the statistical calibration and validation of models in these classes, and finally, the prediction of key Quantities of Interest (QOIs) relevant to patient survival and the effect of various therapies. The most challenging aspects of this endeavor is that all of these issues often involve confounding uncertainties: in observational data, in model parameters, in model selection, and in the features targeted in the prediction. Our approach can be referred to as "model agnostic" in that no single model is advocated; rather, a general approach that explores powerful mixture-theory representations of tissue behavior while accounting for a range of relevant biological factors is presented, which leads to many potentially predictive models. Then representative classes are identified which provide a starting point for the implementation of OPAL, the Occam Plausibility Algorithm (OPAL) which enables the modeler to select the most plausible models (for given data) and to determine if the model is a valid tool for predicting tumor growth and morphology ( in vivo ). All of these approaches account for uncertainties in the model, the observational data, the model parameters, and the target QOI. We demonstrate these processes by comparing a list of models for tumor growth, including reaction-diffusion models, phase-fields models, and models with and without mechanical deformation effects, for glioma growth measured in murine experiments. Examples are provided that exhibit quite acceptable predictions of tumor growth in laboratory
Gompertzian stochastic model with delay effect to cervical cancer growth
International Nuclear Information System (INIS)
Mazlan, Mazma Syahidatul Ayuni binti; Rosli, Norhayati binti; Bahar, Arifah
2015-01-01
In this paper, a Gompertzian stochastic model with time delay is introduced to describe the cervical cancer growth. The parameters values of the mathematical model are estimated via Levenberg-Marquardt optimization method of non-linear least squares. We apply Milstein scheme for solving the stochastic model numerically. The efficiency of mathematical model is measured by comparing the simulated result and the clinical data of cervical cancer growth. Low values of Mean-Square Error (MSE) of Gompertzian stochastic model with delay effect indicate good fits
Gompertzian stochastic model with delay effect to cervical cancer growth
Energy Technology Data Exchange (ETDEWEB)
Mazlan, Mazma Syahidatul Ayuni binti; Rosli, Norhayati binti [Faculty of Industrial Sciences and Technology, Universiti Malaysia Pahang, Lebuhraya Tun Razak, 26300 Gambang, Pahang (Malaysia); Bahar, Arifah [Department of Mathematical Sciences, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor and UTM Centre for Industrial and Applied Mathematics (UTM-CIAM), Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia)
2015-02-03
In this paper, a Gompertzian stochastic model with time delay is introduced to describe the cervical cancer growth. The parameters values of the mathematical model are estimated via Levenberg-Marquardt optimization method of non-linear least squares. We apply Milstein scheme for solving the stochastic model numerically. The efficiency of mathematical model is measured by comparing the simulated result and the clinical data of cervical cancer growth. Low values of Mean-Square Error (MSE) of Gompertzian stochastic model with delay effect indicate good fits.
A new model for simulating growth in fish
Directory of Open Access Journals (Sweden)
Johannes Hamre
2014-01-01
Full Text Available A real dynamic population model calculates change in population sizes independent of time. The Beverton & Holt (B&H model commonly used in fish assessment includes the von Bertalanffy growth function which has age or accumulated time as an independent variable. As a result the B&H model has to assume constant fish growth. However, growth in fish is highly variable depending on food availability and environmental conditions. We propose a new growth model where the length increment of fish living under constant conditions and unlimited food supply, decreases linearly with increasing fish length until it reaches zero at a maximal fish length. The model is independent of time and includes a term which accounts for the environmental variation. In the present study, the model was validated in zebrafish held at constant conditions. There was a good fit of the model to data on observed growth in Norwegian spring spawning herring, capelin from the Barents Sea, North Sea herring and in farmed coastal cod. Growth data from Walleye Pollock from the Eastern Bering Sea and blue whiting from the Norwegian Sea also fitted reasonably well to the model, whereas data from cod from the North Sea showed a good fit to the model only above a length of 70 cm. Cod from the Barents Sea did not grow according to the model. The last results can be explained by environmental factors and variable food availability in the time under study. The model implicates that the efficiency of energy conversion from food decreases as the individual animal approaches its maximal length and is postulated to represent a natural law of fish growth.
Fracture Mechanical Markov Chain Crack Growth Model
DEFF Research Database (Denmark)
Gansted, L.; Brincker, Rune; Hansen, Lars Pilegaard
1991-01-01
propagation process can be described by a discrete space Markov theory. The model is applicable to deterministic as well as to random loading. Once the model parameters for a given material have been determined, the results can be used for any structure as soon as the geometrical function is known....
Mediation Analysis in a Latent Growth Curve Modeling Framework
von Soest, Tilmann; Hagtvet, Knut A.
2011-01-01
This article presents several longitudinal mediation models in the framework of latent growth curve modeling and provides a detailed account of how such models can be constructed. Logical and statistical challenges that might arise when such analyses are conducted are also discussed. Specifically, we discuss how the initial status (intercept) and…
Directory of Open Access Journals (Sweden)
Andrew K. Wills
2016-04-01
Full Text Available Abstract Background Regression models are widely used to link serial measures of anthropometric size or changes in size to a later outcome. Different parameterisations of these models enable one to target different questions about the effect of growth, however, their interpretation can be challenging. Our objective was to formulate and classify several sets of parameterisations by their underlying growth pattern contrast, and to discuss their utility using an expository example. Methods We describe and classify five sets of model parameterisations in accordance with their underlying growth pattern contrast (conditional growth; being bigger v being smaller; becoming bigger and staying bigger; growing faster v being bigger; becoming and staying bigger versus being bigger. The contrasts are estimated by including different sets of repeated measures of size and changes in size in a regression model. We illustrate these models in the setting of linking infant growth (measured on 6 occasions: birth, 6 weeks, 3, 6, 12 and 24 months in weight-for-height-for-age z-scores to later childhood overweight at 8y using complete cases from the Norwegian Childhood Growth study (n = 900. Results In our expository example, conditional growth during all periods, becoming bigger in any interval and staying bigger through infancy, and being bigger from birth were all associated with higher odds of later overweight. The highest odds of later overweight occurred for individuals who experienced high conditional growth or became bigger in the 3 to 6 month period and stayed bigger, and those who were bigger from birth to 24 months. Comparisons between periods and between growth patterns require large sample sizes and need to consider how to scale associations to make comparisons fair; with respect to the latter, we show one approach. Conclusion Studies interested in detrimental growth patterns may gain extra insight from reporting several sets of growth pattern
Models of the Economic Growth and their Relevance
Directory of Open Access Journals (Sweden)
Nicolae MOROIANU
2012-06-01
Full Text Available Until few years ago, the economic growth was something perfect normal, part of an era marked by the transformation speed. Normality itself has been transformed and we currently are influenced by other rules, unknown yet, which should answer the question: “How do we return to the economic growth?” The economic growth and the models aiming to solve this problem concern the economic history even since its beginnings. In this paper we would like to find out what is the relevance that the well-known macroeconomic models still have and which might be their applicability level in a framework created by a black swan event type.
Modeling truck traffic volume growth congestion.
2009-05-01
Modeling of the statewide transportation system is an important element in understanding issues and programming of funds to thwart potential congestion. As Alabama grows its manufacturing economy, the number of heavy vehicles traversing its highways ...
Another brick in the cell wall: biosynthesis dependent growth model.
Directory of Open Access Journals (Sweden)
Adelin Barbacci
Full Text Available Expansive growth of plant cell is conditioned by the cell wall ability to extend irreversibly. This process is possible if (i a tensile stress is developed in the cell wall due to the coupling effect between turgor pressure and the modulation of its mechanical properties through enzymatic and physicochemical reactions and if (ii new cell wall elements can be synthesized and assembled to the existing wall. In other words, expansive growth is the result of coupling effects between mechanical, thermal and chemical energy. To have a better understanding of this process, models must describe the interplay between physical or mechanical variable with biological events. In this paper we propose a general unified and theoretical framework to model growth in function of energy forms and their coupling. This framework is based on irreversible thermodynamics. It is then applied to model growth of the internodal cell of Chara corallina modulated by changes in pressure and temperature. The results describe accurately cell growth in term of length increment but also in term of cell pectate biosynthesis and incorporation to the expanding wall. Moreover, the classical growth model based on Lockhart's equation such as the one proposed by Ortega, appears as a particular and restrictive case of the more general growth equation developed in this paper.
Xu, Q.; Hou, Z.; Maltamo, M.; Tokola, T.
2015-12-01
Diameter distributions of trees are important indicators of current forest stand structure and future dynamics. A new method was proposed in the study to combine the diameter distributions derived from the area-based approach (ABA) and the diameter distribution derived from the individual tree detection (ITD) in order to obtain more accurate forest stand attributes. Since dominant trees can be reliably detected and measured by the Lidar data via the ITD, the focus of the study is to retrieve the suppressed trees (trees that were missed by the ITD) from the ABA. Replacement and histogram matching were respectively employed at the plot level to retrieve the suppressed trees. Cut point was detected from the ITD-derived diameter distribution for each sample plot to distinguish dominant trees from the suppressed trees. The results showed that calibrated diameter distributions were more accurate in terms of error index and the entire growing stock estimates. Compared with the best performer between the ABA and the ITD, calibrated diameter distributions decreased the relative RMSE of the estimated entire growing stock, saw log and pulpwood fractions by 2.81%, 3.05% and 7.73% points respectively. Calibration improved the estimation of pulpwood fraction significantly, resulting in a negligible bias of the estimated entire growing stock.
Quadratic tracer dynamical models tobacco growth
International Nuclear Information System (INIS)
Qiang Jiyi; Hua Cuncai; Wang Shaohua
2011-01-01
In order to study the non-uniformly transferring process of some tracer dosages, we assume that the absorption of some tracer by tobacco is a quadratic function of the tracer quantity of the tracer in the case of fast absorption, whereas the exclusion of the tracer from tobacco is a linear function of the tracer quantity in the case of slow exclusion, after the tracer is introduced into tobacco once at zero time. A single-compartment quadratic dynamical model of Logistic type is established for the leaves of tobacco. Then, a two-compartment quadratic dynamical model is established for leaves and calms of the tobacco. Qualitative analysis of the models shows that the tracer applied to the leaves of the tobacco is excluded finally; however, the tracer stays at the tobacco for finite time. Two methods are also given for computing the parameters in the models. Finally, the results of the models are verified by the 32 P experiment for the absorption of tobacco. (authors)
Modeling and simulation of Si crystal growth from melt
Energy Technology Data Exchange (ETDEWEB)
Liu, Lijun; Liu, Xin; Li, Zaoyang [National Engineering Research Center for Fluid Machinery and Compressors, School of Energy and Power Engineering, Xi' an Jiaotong University, Xi' an, Shaanxi 710049 (China); Miyazawa, Hiroaki; Nakano, Satoshi; Kakimoto, Koichi [Research Institute for Applied Mechanics, Kyushu University, Kasuga 816-8580 (Japan)
2009-07-01
A numerical simulator was developed with a global model of heat transfer for any crystal growth taking place at high temperature. Convective, conductive and radiative heat transfers in the furnace are solved together in a conjugated way by a finite volume method. A three-dimensional (3D) global model was especially developed for simulation of heat transfer in any crystal growth with 3D features. The model enables 3D global simulation be conducted with moderate requirement of computer resources. The application of this numerical simulator to a CZ growth and a directional solidification process for Si crystals, the two major production methods for crystalline Si for solar cells, was introduced. Some typical results were presented, showing the importance and effectiveness of numerical simulation in analyzing and improving these kinds of Si crystal growth processes from melt. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Growth Curve Models and Applications : Indian Statistical Institute
2017-01-01
Growth curve models in longitudinal studies are widely used to model population size, body height, biomass, fungal growth, and other variables in the biological sciences, but these statistical methods for modeling growth curves and analyzing longitudinal data also extend to general statistics, economics, public health, demographics, epidemiology, SQC, sociology, nano-biotechnology, fluid mechanics, and other applied areas. There is no one-size-fits-all approach to growth measurement. The selected papers in this volume build on presentations from the GCM workshop held at the Indian Statistical Institute, Giridih, on March 28-29, 2016. They represent recent trends in GCM research on different subject areas, both theoretical and applied. This book includes tools and possibilities for further work through new techniques and modification of existing ones. The volume includes original studies, theoretical findings and case studies from a wide range of app lied work, and these contributions have been externally r...
Benchmark data set for wheat growth models
DEFF Research Database (Denmark)
Asseng, S; Ewert, F.; Martre, P
2015-01-01
The data set includes a current representative management treatment from detailed, quality-tested sentinel field experiments with wheat from four contrasting environments including Australia, The Netherlands, India and Argentina. Measurements include local daily climate data (solar radiation, max...... analysis with 26 models and 30 years (1981-2010) for each location, for elevated atmospheric CO2 and temperature changes, a heat stress sensitivity analysis at anthesis, and a sensitivity analysis with soil and crop management variations and a Global Climate Model end-century scenario....
A mathematical model of microalgae growth in cylindrical photobioreactor
Bakeri, Noorhadila Mohd; Jamaian, Siti Suhana
2017-08-01
Microalgae are unicellular organisms, which exist individually or in chains or groups but can be utilized in many applications. Researchers have done various efforts in order to increase the growth rate of microalgae. Microalgae have a potential as an effective tool for wastewater treatment, besides as a replacement for natural fuel such as coal and biodiesel. The growth of microalgae can be estimated by using Geider model, which this model is based on photosynthesis irradiance curve (PI-curve) and focused on flat panel photobioreactor. Therefore, in this study a mathematical model for microalgae growth in cylindrical photobioreactor is proposed based on the Geider model. The light irradiance is the crucial part that affects the growth rate of microalgae. The absorbed photon flux will be determined by calculating the average light irradiance in a cylindrical system illuminated by unidirectional parallel flux and considering the cylinder as a collection of differential parallelepipeds. Results from this study showed that the specific growth rate of microalgae increases until the constant level is achieved. Therefore, the proposed mathematical model can be used to estimate the rate of microalgae growth in cylindrical photobioreactor.
Modelling breast cancer tumour growth for a stable disease population.
Isheden, Gabriel; Humphreys, Keith
2017-01-01
Statistical models of breast cancer tumour progression have been used to further our knowledge of the natural history of breast cancer, to evaluate mammography screening in terms of mortality, to estimate overdiagnosis, and to estimate the impact of lead-time bias when comparing survival times between screen detected cancers and cancers found outside of screening programs. Multi-state Markov models have been widely used, but several research groups have proposed other modelling frameworks based on specifying an underlying biological continuous tumour growth process. These continuous models offer some advantages over multi-state models and have been used, for example, to quantify screening sensitivity in terms of mammographic density, and to quantify the effect of body size covariates on tumour growth and time to symptomatic detection. As of yet, however, the continuous tumour growth models are not sufficiently developed and require extensive computing to obtain parameter estimates. In this article, we provide a detailed description of the underlying assumptions of the continuous tumour growth model, derive new theoretical results for the model, and show how these results may help the development of this modelling framework. In illustrating the approach, we develop a model for mammography screening sensitivity, using a sample of 1901 post-menopausal women diagnosed with invasive breast cancer.
A mathematical model of the growth of uterine myomas.
Chen, C Y; Ward, J P
2014-12-01
Uterine myomas or fibroids are common, benign smooth muscle tumours that can grow to 10 cm or more in diameter and are routinely removed surgically. They are typically slow- growing, well-vascularised, spherical tumours that, on a macro-scale, are a structurally uniform, hard elastic material. We present a multi-phase mathematical model of a fully vascularised myoma growing within a surrounding elastic tissue. Adopting a continuum approach, the model assumes the conservation of mass and momentum of four phases, namely cells/collagen, extracellular fluid, arterial and venous phases. The cell/collagen phase is treated as a poro-elastic material, based on a linear stress-strain relationship, and Darcy's law is applied to describe flow in the extracellular fluid and the two vascular phases. The supply of extracellular fluid is dependent on the capillary flow rate and mean capillary pressure expressed in terms of the arterial and venous pressures. Cell growth and division is limited to the myoma domain and dependent on the local stress in the material. The resulting model consists of a system of nonlinear partial differential equations with two moving boundaries. Numerical solutions of the model successfully reproduce qualitatively the clinically observed three-phase "fast-slow-fast" growth profile that is typical for myomas. The results suggest that this growth profile requires stress-induced resistance to growth by the surrounding tissue and a switch-like cell growth response to stress. Analysis of large-time solutions reveal that while there is a functioning vasculature throughout the myoma, exponential growth results, otherwise power-law growth is predicted. An extensive survey of the effect of parameters on model solutions is also presented, and in particular, the enhanced growth caused by factors such as oestrogen is predicted by the model.
Non-linear Growth Models in Mplus and SAS
Grimm, Kevin J.; Ram, Nilam
2013-01-01
Non-linear growth curves or growth curves that follow a specified non-linear function in time enable researchers to model complex developmental patterns with parameters that are easily interpretable. In this paper we describe how a variety of sigmoid curves can be fit using the Mplus structural modeling program and the non-linear mixed-effects modeling procedure NLMIXED in SAS. Using longitudinal achievement data collected as part of a study examining the effects of preschool instruction on academic gain we illustrate the procedures for fitting growth models of logistic, Gompertz, and Richards functions. Brief notes regarding the practical benefits, limitations, and choices faced in the fitting and estimation of such models are included. PMID:23882134
Small Business Training Models for Community Growth.
Jellison, Holly M., Ed.
Nine successful community college programs for small business management training are described in this report in terms of their college and economic context, purpose, offerings, delivery modes, operating and marketing strategies, community outreach, support services, faculty and staff, evaluation, and future directions. The model programs are…
Reserve growth in oil pools of Alberta : model and forecast
Energy Technology Data Exchange (ETDEWEB)
Verma, M.; Cook, T. [United States Geological Survey, Denver, CO (United States). Central Region
2010-09-15
This paper presented a reserve growth study that was conducted on oil pools in Alberta, Canada. Historical oil reserve data were evaluated to assess the potential for future reserve growth in both pools and fields, and reserve growth models and functions were developed to better forecast hydrocarbon volumes. The study also considered the sensitivity of reserve growth to such factors as pool size, porosity, and oil gravity. From 1960 to 2005, the reported known recoverable oil in Alberta, excluding the Athabasca oil sands and including only pools with adequate data, increased from 4.2 to 13.9 billion barrels of oil (BBO). New discoveries contributed 3.7 BBO and reserve growth added 6 BBO. Most reserve growth occurred in pools with more than 125,000 barrels of oil. Light-oil pools account for most of the total known oil volume and consequently showed the lowest growth. Pools with greater than 30 percent porosity grew more than pools with lower porosity reservoirs. Oil field growth was found to be almost twice that of pool growth, possibly because the analysis evaluated fields with two or more pools discovered in different years. The growth in oil volumes in Alberta pools is projected to be about 454 million barrels of oil in the period from 2006 to 2010. Over a 25-year period, the cumulative reserve growth in Alberta oil pools was substantially lower than other major petroleum-producing regions, but the growth at the field level compares well. 8 refs., 2 tabs., 9 figs.
Populational Growth Models Proportional to Beta Densities with Allee Effect
Aleixo, Sandra M.; Rocha, J. Leonel; Pestana, Dinis D.
2009-05-01
We consider populations growth models with Allee effect, proportional to beta densities with shape parameters p and 2, where the dynamical complexity is related with the Malthusian parameter r. For p>2, these models exhibit a population dynamics with natural Allee effect. However, in the case of 1
models do not include this effect. In order to inforce it, we present some alternative models and investigate their dynamics, presenting some important results.
Model for the growth of the world airline network
Verma, T.; Araújo, N. A. M.; Nagler, J.; Andrade, J. S.; Herrmann, H. J.
2016-06-01
We propose a probabilistic growth model for transport networks which employs a balance between popularity of nodes and the physical distance between nodes. By comparing the degree of each node in the model network and the World Airline Network (WAN), we observe that the difference between the two is minimized for α≈2. Interestingly, this is the value obtained for the node-node correlation function in the WAN. This suggests that our model explains quite well the growth of airline networks.
Surface-bounded growth modeling applied to human mandibles
DEFF Research Database (Denmark)
Andresen, Per Rønsholt
1999-01-01
This thesis presents mathematical and computational techniques for three dimensional growth modeling applied to human mandibles. The longitudinal shape changes make the mandible a complex bone. The teeth erupt and the condylar processes change direction, from pointing predominantly backward...... of the common features. 3.model the process that moves the matched points (growth modeling). A local shape feature called crest line has shown itself to be structurally stable on mandibles. Registration of crest lines (from different mandibles) results in a sparse deformation field, which must be interpolated...... old mandible based on the 3 month old scan. When using successively more recent scans as basis for the model the error drops to 2.0 mm for the 11 years old scan. Thus, it seems reasonable to assume that the mandibular growth is linear....
Using Calculus to Model the Growth of L. Plantarum Bacteria
Directory of Open Access Journals (Sweden)
Erin Carey
2009-01-01
Full Text Available Experimental data for the growth of Lactobacillus plantarum bacteria have been obtained over time, creating the need for mathematical means to model this data. We use the Gompertz model because it is a sigmoid function for a time series, where growth is slowest at the start and end of a time period. The Gompertz model is especially useful because it defines specific parameters that characterize the S-shaped curve. In addition, the Gompertz model uses relative growth, which is the logarithm of the given population compared to the initial population. This reflects the fact that bacteria grow exponentially. The important parameters that were found were the lag time and the asymptote.
An evolving network model with modular growth
International Nuclear Information System (INIS)
Zou Zhi-Yun; Liu Peng; Lei Li; Gao Jian-Zhi
2012-01-01
In this paper, we propose an evolving network model growing fast in units of module, according to the analysis of the evolution characteristics in real complex networks. Each module is a small-world network containing several interconnected nodes and the nodes between the modules are linked by preferential attachment on degree of nodes. We study the modularity measure of the proposed model, which can be adjusted by changing the ratio of the number of inner-module edges and the number of inter-module edges. In view of the mean-field theory, we develop an analytical function of the degree distribution, which is verified by a numerical example and indicates that the degree distribution shows characteristics of the small-world network and the scale-free network distinctly at different segments. The clustering coefficient and the average path length of the network are simulated numerically, indicating that the network shows the small-world property and is affected little by the randomness of the new module. (interdisciplinary physics and related areas of science and technology)
Sensitivity of Fit Indices to Misspecification in Growth Curve Models
Wu, Wei; West, Stephen G.
2010-01-01
This study investigated the sensitivity of fit indices to model misspecification in within-individual covariance structure, between-individual covariance structure, and marginal mean structure in growth curve models. Five commonly used fit indices were examined, including the likelihood ratio test statistic, root mean square error of…
Modelling primary branch growth based on a multilevel nonlinear ...
African Journals Online (AJOL)
In addition to random effects, various time series correlation structures were evaluated to account for residual autocorrelation, and the AR(1) and ARMA(1,1) structures were selected for the branch diameter and length growth models, respectively. Model validation results using an independent data set confirmed that ...
Modeling and forecasting mortality with economic growth : a multipopulation approach
Boonen, T.J.; Li, H.
2017-01-01
Research on mortality modeling of multiple populations focuses mainly on extrapolating past mortality trends and summarizing these trends by one or more common latent factors. This article proposes a multipopulation stochastic mortality model that uses the explanatory power of economic growth. In
Growth models for six Eucalyptus species in Angola | Delgado ...
African Journals Online (AJOL)
This study developed growth models for Eucalyptus saligna Sm., E. camaldulensis Dehnh., E. macarthurii H.Deane & Maiden, E. resinifera Sm., E. siderophloia Benth. and E. grandis Hill ex. Maiden, for the central highlands of Angola, and used these models to simulate the development of stand characteristics.
Kinetic models of cell growth, substrate utilization and bio ...
African Journals Online (AJOL)
Bio-decolorization kinetic studies of distillery effluent in a batch culture were conducted using Aspergillus fumigatus. A simple model was proposed using the Logistic Equation for the growth, Leudeking-Piret kinetics for bio-decolorization, and also for substrate utilization. The proposed models appeared to provide a suitable ...
A thermodynamic model for growth mechanisms of multiwall carbon nanotubes.
Energy Technology Data Exchange (ETDEWEB)
Kaatz, Forrest H.; Overmyer, Donald L.; Siegal, Michael P.
2006-02-01
Multiwall carbon nanotubes are grown via thermal chemical vapor deposition between temperatures of 630 and 830 C using acetylene in nitrogen as the carbon source. This process is modeled using classical thermodynamics to explain the total carbon deposition as a function of time and temperature. An activation energy of 1.60 eV is inferred for nanotube growth after considering the carbon solubility term. Scanning electron microscopy shows growth with diameters increasing linearly with time. Transmission electron microscopy and Raman spectroscopy show multiwall nanotubes surrounded by a glassy-carbon sheath, which grows with increasing wall thickness as growth temperatures and times rise.
Thermodynamic model for growth mechanisms of multiwall carbon nanotubes
Kaatz, F. H.; Siegal, M. P.; Overmyer, D. L.; Provencio, P. P.; Tallant, D. R.
2006-12-01
Multiwall carbon nanotubes are grown via thermal chemical vapor deposition between temperatures of 630 and 830°C using acetylene in nitrogen as the carbon source. This process is modeled using classical thermodynamics to explain the total carbon deposition as a function of time and temperature. An activation energy of 1.60eV is inferred for nanotube growth after considering the carbon solubility term. Scanning electron microscopy shows growth with diameters increasing linearly with time. Transmission electron microscopy and Raman spectroscopy show multiwall nanotubes surrounded by a glassy-carbon sheath, which grows with increasing wall thickness as growth temperatures and times rise.
Spending Natural Resource Revenues in an Altruistic Growth Model
DEFF Research Database (Denmark)
Frederiksen, Elisabeth Hermann
This paper examines how revenues from a natural resource interact with growth and welfare in an overlapping generations model with altruism. The revenues are allocated between public productive services and direct transfers to members of society by spending policies. We analyze how these policies...... influence the dynamics, and how the dynamics are influenced by the abundance of the revenue. Abundant revenues may harm growth, but growth and welfare can be oppositely affected. We also provide the socially optimal policy. Overall, the analysis suggests that variation in the strength of altruism...
Government technology push in agribusiness: a model of endogenous growth
Directory of Open Access Journals (Sweden)
Francisco Venegas Martínez
2008-10-01
Full Text Available This paper develops a model of endogenous growth where the government acts as a promoting agent to boost technology in agribusiness. In the framework of a monetary economy, the optimal level of government spending to enhance technology in the agricultural industry is characterized. Moreover the impact of such a spending on economic welfare is assessed. Finally, a number of agro-oriented policies to increase growth in the sector are established.
Alexandrium minutum growth controlled by phosphorus An applied model
Chapelle, Annie; Labry, Claire; Sourisseau, Marc; Lebreton, Carole; Youenou, Agnes; Crassous, Marie-pierre
2010-01-01
Toxic algae are a worldwide problem threatening aquaculture public health and tourism Alexandrium a toxic dinoflagellate proliferates in Northwest France estuaries (i e the Penze estuary) causing Paralytic Shellfish Poisoning events Vegetative growth and in particular the role of nutrient uptake and growth rate are crucial parameters to understand toxic blooms With the goal of modelling in situ Alexandrium blooms related to environmental parameters we first try to calibrate a zero-dimensional...
Reactor scale modeling of multi-walled carbon nanotube growth
International Nuclear Information System (INIS)
Lombardo, Jeffrey J.; Chiu, Wilson K.S.
2011-01-01
As the mechanisms of carbon nanotube (CNT) growth becomes known, it becomes important to understand how to implement this knowledge into reactor scale models to optimize CNT growth. In past work, we have reported fundamental mechanisms and competing deposition regimes that dictate single wall carbon nanotube growth. In this study, we will further explore the growth of carbon nanotubes with multiple walls. A tube flow chemical vapor deposition reactor is simulated using the commercial software package COMSOL, and considered the growth of single- and multi-walled carbon nanotubes. It was found that the limiting reaction processes for multi-walled carbon nanotubes change at different temperatures than the single walled carbon nanotubes and it was shown that the reactions directly governing CNT growth are a limiting process over certain parameters. This work shows that the optimum conditions for CNT growth are dependent on temperature, chemical concentration, and the number of nanotube walls. Optimal reactor conditions have been identified as defined by (1) a critical inlet methane concentration that results in hydrogen abstraction limited versus hydrocarbon adsorption limited reaction kinetic regime, and (2) activation energy of reaction for a given reactor temperature and inlet methane concentration. Successful optimization of a CNT growth processes requires taking all of those variables into account.
Modelling grain growth in the framework of Rational Extended Thermodynamics
International Nuclear Information System (INIS)
Kertsch, Lukas; Helm, Dirk
2016-01-01
Grain growth is a significant phenomenon for the thermomechanical processing of metals. Since the mobility of the grain boundaries is thermally activated and energy stored in the grain boundaries is released during their motion, a mutual interaction with the process conditions occurs. To model such phenomena, a thermodynamic framework for the representation of thermomechanical coupling phenomena in metals including a microstructure description is required. For this purpose, Rational Extended Thermodynamics appears to be a useful tool. We apply an entropy principle to derive a thermodynamically consistent model for grain coarsening due to the growth and shrinkage of individual grains. Despite the rather different approaches applied, we obtain a grain growth model which is similar to existing ones and can be regarded as a thermodynamic extension of that by Hillert (1965) to more general systems. To demonstrate the applicability of the model, we compare our simulation results to grain growth experiments in pure copper by different authors, which we are able to reproduce very accurately. Finally, we study the implications of the energy release due to grain growth on the energy balance. The present unified approach combining a microstructure description and continuum mechanics is ready to be further used to develop more elaborate material models for complex thermo-chemo-mechanical coupling phenomena. (paper)
Modelling grain growth in the framework of Rational Extended Thermodynamics
Kertsch, Lukas; Helm, Dirk
2016-05-01
Grain growth is a significant phenomenon for the thermomechanical processing of metals. Since the mobility of the grain boundaries is thermally activated and energy stored in the grain boundaries is released during their motion, a mutual interaction with the process conditions occurs. To model such phenomena, a thermodynamic framework for the representation of thermomechanical coupling phenomena in metals including a microstructure description is required. For this purpose, Rational Extended Thermodynamics appears to be a useful tool. We apply an entropy principle to derive a thermodynamically consistent model for grain coarsening due to the growth and shrinkage of individual grains. Despite the rather different approaches applied, we obtain a grain growth model which is similar to existing ones and can be regarded as a thermodynamic extension of that by Hillert (1965) to more general systems. To demonstrate the applicability of the model, we compare our simulation results to grain growth experiments in pure copper by different authors, which we are able to reproduce very accurately. Finally, we study the implications of the energy release due to grain growth on the energy balance. The present unified approach combining a microstructure description and continuum mechanics is ready to be further used to develop more elaborate material models for complex thermo-chemo-mechanical coupling phenomena.
Some Limits Using Random Slope Models to Measure Academic Growth
Directory of Open Access Journals (Sweden)
Daniel B. Wright
2017-11-01
Full Text Available Academic growth is often estimated using a random slope multilevel model with several years of data. However, if there are few time points, the estimates can be unreliable. While using random slope multilevel models can lower the variance of the estimates, these procedures can produce more highly erroneous estimates—zero and negative correlations with the true underlying growth—than using ordinary least squares estimates calculated for each student or school individually. An example is provided where schools with increasing graduation rates are estimated to have negative growth and vice versa. The estimation is worse when the underlying data are skewed. It is recommended that there are at least six time points for estimating growth if using a random slope model. A combination of methods can be used to avoid some of the aberrant results if it is not possible to have six or more time points.
Brexit and the Politics of UK Growth Models
DEFF Research Database (Denmark)
Rosamond, Ben
2018-01-01
Brexit has reopened and repoliticized the debate about future growth models for the UK economy. This contribution argues that this debate is built around historically specific path dependencies that reflect the particular character of public debate about British political economy, while also...... particular attention to the importance of the politics of support. It suggests that recent debate about growth models has been largely subsumed within the politics of Brexit, which has politicized that debate, albeit through the emergent political economy frames that Brexit has provoked. The paper explores...... suggesting that the debate around Brexit takes place at a very distinctive moment in the history of democratic capitalism in Europe. This combination gives the renewed politicization a specific and perhaps perverse character. The paper considers how we should approach debates about growth models, paying...
Modeling of Hybrid Growth Wastewater Bio-reactor
International Nuclear Information System (INIS)
EI Nashaei, S.; Garhyan, P.; Prasad, P.; Abdel Halim, H.S.; Ibrahim, G.
2004-01-01
The attached/suspended growth mixed reactors are considered one of the recently tried approaches to improve the performance of the biological treatment by increasing the volume of the accumulated biomass in terms of attached growth as well as suspended growth. Moreover, the domestic WW can be easily mixed with a high strength non-hazardous industrial wastewater and treated together in these bio-reactors if the need arises. Modeling of Hybrid hybrid growth wastewater reactor addresses the need of understanding the rational of such system in order to achieve better design and operation parameters. This paper aims at developing a heterogeneous mathematical model for hybrid growth system considering the effect of diffusion, external mass transfer, and power input to the system in a rational manner. The model will be based on distinguishing between liquid/solid phase (bio-film and bio-floc). This model would be a step ahead to the fine tuning the design of hybrid systems based on the experimental data of a pilot plant to be implemented in near future
A new method for evaluating forest thinning: growth dominance in managed Pinus resinosa stands
John B. Bradford; Anthony W. D' Amato; Brian J. Palik; Shawn. Fraver
2010-01-01
Growth dominance is a relatively new, simple, quantitative metric of within-stand individual tree growth patterns, and is defined as positive when larger trees in the stand display proportionally greater growth than smaller trees, and negative when smaller trees display proportionally greater growth than larger trees. We examined long-term silvicultural experiments in...
3D Multiscale Modelling of Angiogenesis and Vascular Tumour Growth
Perfahl, H.
2012-11-01
We present a three-dimensional, multiscale model of vascular tumour growth, which couples nutrient/growth factor transport, blood flow, angiogenesis, vascular remodelling, movement of and interactions between normal and tumour cells, and nutrient-dependent cell cycle dynamics within each cell. We present computational simulations which show how a vascular network may evolve and interact with tumour and healthy cells. We also demonstrate how our model may be combined with experimental data, to predict the spatio-temporal evolution of a vascular tumour.
3D Multiscale Modelling of Angiogenesis and Vascular Tumour Growth
Perfahl, H.; Byrne, H. M.; Chen, T.; Estrella, V.; Alarcó n, T.; Lapin, A.; Gatenby, R. A.; Gillies, R. J.; Lloyd, M. C.; Maini, P. K.; Reuss, M.; Owen, M. R.
2012-01-01
We present a three-dimensional, multiscale model of vascular tumour growth, which couples nutrient/growth factor transport, blood flow, angiogenesis, vascular remodelling, movement of and interactions between normal and tumour cells, and nutrient-dependent cell cycle dynamics within each cell. We present computational simulations which show how a vascular network may evolve and interact with tumour and healthy cells. We also demonstrate how our model may be combined with experimental data, to predict the spatio-temporal evolution of a vascular tumour.
Research & development and growth: A Bayesian model averaging analysis
Czech Academy of Sciences Publication Activity Database
Horváth, Roman
2011-01-01
Roč. 28, č. 6 (2011), s. 2669-2673 ISSN 0264-9993. [Society for Non-linear Dynamics and Econometrics Annual Conferencen. Washington DC, 16.03.2011-18.03.2011] R&D Projects: GA ČR GA402/09/0965 Institutional research plan: CEZ:AV0Z10750506 Keywords : Research and development * Growth * Bayesian model averaging Subject RIV: AH - Economic s Impact factor: 0.701, year: 2011 http://library.utia.cas.cz/separaty/2011/E/horvath-research & development and growth a bayesian model averaging analysis.pdf
Some Remarks on Stochastic Versions of the Ramsey Growth Model
Czech Academy of Sciences Publication Activity Database
Sladký, Karel
2012-01-01
Roč. 19, č. 29 (2012), s. 139-152 ISSN 1212-074X R&D Projects: GA ČR GAP402/10/1610; GA ČR GAP402/10/0956; GA ČR GAP402/11/0150 Institutional support: RVO:67985556 Keywords : Economic dynamics * Ramsey growth model with disturbance * stochastic dynamic programming * multistage stochastic programs Subject RIV: BB - Applied Statistics, Operational Research http://library.utia.cas.cz/separaty/2013/E/sladky-some remarks on stochastic versions of the ramsey growth model.pdf
Pollution and economic growth in a model of overlapping generations
Energy Technology Data Exchange (ETDEWEB)
Fisher, Eric O`N. [Department of Economics, The Ohio State University, Columbus, OH (United States); Van Marrewijk, Charles [Department of Economics, Erasmus University, Rotterdam (Netherlands)
1994-01-22
We analyze a model of overlapping generations in which clean air, a pure public consumption good, is used as a private input into production. Although production exhibits constant returns to scale, endogenous growth can occur because the economy has tWO sectors. In a laissez-faire equilibrium, there is no market for pollution rights, and firms appropriate clean air in an arbitrary manner. Growth occurs only if the marginal propensity to save is high enough and the asymptotic share of pollution in the investment sector is zero. Firms generate quasi-rents that are the value of pollution rights. These quasi-rents crowd out investment and slow economic growth. A laissez- faire equilibrium may not support Pareto optimal allocations, but a Pigouvian tax with lump-sum distribution of the resulting revenues does. Hence, a pollution lax yields a double dividend because it can increase both the static efficiency of the economy and its growth rate. 1 fig., 20 refs.
Growth model of Au films on Ru(001)
International Nuclear Information System (INIS)
Canessa, E.; Calmetta, A.
1992-06-01
In an attempt to find generic features on the fractal growth of Au films deposited on Ru(001), a simple simulation model based on irreversible diffusion-limited aggregation (DLA) is discussed. Highly irregular two-dimensional dentritic islands of Au particles that gradually grow on a larger host lattice of Ru particles and have fractal dimension d f approx. 1.70 each, are generated via a multiple had-hoc version of the DLA algorithm for single aggregates. Annealing effects on the islands morphology are reproduced assuming different sticking probabilities at nearest-neighbour lattice sites of Au films on Ru(001). Using simulation data, islands growth are described in analogy to diffusion-limited, precipitate growth with soft impingement of precipities. This leads to analyse thin film island growth kinetics in such fractal systems and to predict a main peak in scattering intensity patterns due to interisland interference. (author). 12 refs, 4 figs
Pollution and economic growth in a model of overlapping generations
International Nuclear Information System (INIS)
Fisher, Eric O'N.; Van Marrewijk, Charles
1994-01-01
We analyze a model of overlapping generations in which clean air, a pure public consumption good, is used as a private input into production. Although production exhibits constant returns to scale, endogenous growth can occur because the economy has tWO sectors. In a laissez-faire equilibrium, there is no market for pollution rights, and firms appropriate clean air in an arbitrary manner. Growth occurs only if the marginal propensity to save is high enough and the asymptotic share of pollution in the investment sector is zero. Firms generate quasi-rents that are the value of pollution rights. These quasi-rents crowd out investment and slow economic growth. A laissez- faire equilibrium may not support Pareto optimal allocations, but a Pigouvian tax with lump-sum distribution of the resulting revenues does. Hence, a pollution lax yields a double dividend because it can increase both the static efficiency of the economy and its growth rate. 1 fig., 20 refs
A 2-D nucleation-growth model of spheroidal graphite
International Nuclear Information System (INIS)
Lacaze, Jacques; Bourdie, Jacques; Castro-Román, Manuel Jesus
2017-01-01
Analysis of recent experimental investigations, in particular by transmission electron microscopy, suggests spheroidal graphite grows by 2-D nucleation of new graphite layers at the outer surface of the nodules. These layers spread over the surface along the prismatic direction of graphite which is the energetically preferred growth direction of graphite when the apparent growth direction of the nodules is along the basal direction of graphite. 2-D nucleation-growth models first developed for precipitation of pure substances are then adapted to graphite growth from the liquid in spheroidal graphite cast irons. Lateral extension of the new graphite layers is controlled by carbon diffusion in the liquid. This allows describing quantitatively previous experimental results giving strong support to this approach.
Modeling and Forecasting Mortality With Economic Growth: A Multipopulation Approach.
Boonen, Tim J; Li, Hong
2017-10-01
Research on mortality modeling of multiple populations focuses mainly on extrapolating past mortality trends and summarizing these trends by one or more common latent factors. This article proposes a multipopulation stochastic mortality model that uses the explanatory power of economic growth. In particular, we extend the Li and Lee model (Li and Lee 2005) by including economic growth, represented by the real gross domestic product (GDP) per capita, to capture the common mortality trend for a group of populations with similar socioeconomic conditions. We find that our proposed model provides a better in-sample fit and an out-of-sample forecast performance. Moreover, it generates lower (higher) forecasted period life expectancy for countries with high (low) GDP per capita than the Li and Lee model.
A Discrete Monetary Economic Growth Model with the MIU Approach
Directory of Open Access Journals (Sweden)
Wei-Bin Zhang
2008-01-01
Full Text Available This paper proposes an alternative approach to economic growth with money. The production side is the same as the Solow model, the Ramsey model, and the Tobin model. But we deal with behavior of consumers differently from the traditional approaches. The model is influenced by the money-in-the-utility (MIU approach in monetary economics. It provides a mechanism of endogenous saving which the Solow model lacks and avoids the assumption of adding up utility over a period of time upon which the Ramsey approach is based.
Eye growth and myopia development: Unifying theory and Matlab model.
Hung, George K; Mahadas, Kausalendra; Mohammad, Faisal
2016-03-01
The aim of this article is to present an updated unifying theory of the mechanisms underlying eye growth and myopia development. A series of model simulation programs were developed to illustrate the mechanism of eye growth regulation and myopia development. Two fundamental processes are presumed to govern the relationship between physiological optics and eye growth: genetically pre-programmed signaling and blur feedback. Cornea/lens is considered to have only a genetically pre-programmed component, whereas eye growth is considered to have both a genetically pre-programmed and a blur feedback component. Moreover, based on the Incremental Retinal-Defocus Theory (IRDT), the rate of change of blur size provides the direction for blur-driven regulation. The various factors affecting eye growth are shown in 5 simulations: (1 - unregulated eye growth): blur feedback is rendered ineffective, as in the case of form deprivation, so there is only genetically pre-programmed eye growth, generally resulting in myopia; (2 - regulated eye growth): blur feedback regulation demonstrates the emmetropization process, with abnormally excessive or reduced eye growth leading to myopia and hyperopia, respectively; (3 - repeated near-far viewing): simulation of large-to-small change in blur size as seen in the accommodative stimulus/response function, and via IRDT as well as nearwork-induced transient myopia (NITM), leading to the development of myopia; (4 - neurochemical bulk flow and diffusion): release of dopamine from the inner plexiform layer of the retina, and the subsequent diffusion and relay of neurochemical cascade show that a decrease in dopamine results in a reduction of proteoglycan synthesis rate, which leads to myopia; (5 - Simulink model): model of genetically pre-programmed signaling and blur feedback components that allows for different input functions to simulate experimental manipulations that result in hyperopia, emmetropia, and myopia. These model simulation programs
Modelling of strongly coupled particle growth and aggregation
International Nuclear Information System (INIS)
Gruy, F; Touboul, E
2013-01-01
The mathematical modelling of the dynamics of particle suspension is based on the population balance equation (PBE). PBE is an integro-differential equation for the population density that is a function of time t, space coordinates and internal parameters. Usually, the particle is characterized by a unique parameter, e.g. the matter volume v. PBE consists of several terms: for instance, the growth rate and the aggregation rate. So, the growth rate is a function of v and t. In classical modelling, the growth and the aggregation are independently considered, i.e. they are not coupled. However, current applications occur where the growth and the aggregation are coupled, i.e. the change of the particle volume with time is depending on its initial value v 0 , that in turn is related to an aggregation event. As a consequence, the dynamics of the suspension does not obey the classical Von Smoluchowski equation. This paper revisits this problem by proposing a new modelling by using a bivariate PBE (with two internal variables: v and v 0 ) and by solving the PBE by means of a numerical method and Monte Carlo simulations. This is applied to a physicochemical system with a simple growth law and a constant aggregation kernel.
Application of a Snow Growth Model to Radar Remote Sensing
Erfani, E.; Mitchell, D. L.
2014-12-01
Microphysical growth processes of diffusion, aggregation and riming are incorporated analytically in a steady-state snow growth model (SGM) to solve the zeroth- and second- moment conservation equations with respect to mass. The SGM is initiated by radar reflectivity (Zw), supersaturation, temperature, and a vertical profile of the liquid water content (LWC), and it uses a gamma size distribution (SD) to predict the vertical evolution of size spectra. Aggregation seems to play an important role in the evolution of snowfall rates and the snowfall rates produced by aggregation, diffusion and riming are considerably greater than those produced by diffusion and riming alone, demonstrating the strong interaction between aggregation and riming. The impact of ice particle shape on particle growth rates and fall speeds is represented in the SGM in terms of ice particle mass-dimension (m-D) power laws (m = αDβ). These growth rates are qualitatively consistent with empirical growth rates, with slower (faster) growth rates predicted for higher (lower) β values. In most models, β is treated constant for a given ice particle habit, but it is well known that β is larger for the smaller crystals. Our recent work quantitatively calculates β and α for cirrus clouds as a function of D where the m-D expression is a second-order polynomial in log-log space. By adapting this method to the SGM, the ice particle growth rates and fall speeds are predicted more accurately. Moreover, the size spectra predicted by the SGM are in good agreement with those from aircraft measurements during Lagrangian spiral descents through frontal clouds, indicating the successful modeling of microphysical processes. Since the lowest Zw over complex topography is often significantly above cloud base, the precipitation is often underestimated by radar quantitative precipitation estimates (QPE). Our SGM is capable of being initialized with Zw at the lowest reliable radar echo and consequently improves
National Research Council Canada - National Science Library
Abate, Christopher
2004-01-01
...) data with a hybrid adjusted cost growth (ACG) model. In addition, an analysis of acquisition reform initiatives during the treatment period was conducted to determine if reform efforts impacted missile system cost growth. A pre-reform...
Modeling of dislocation dynamics in germanium Czochralski growth
Artemyev, V. V.; Smirnov, A. D.; Kalaev, V. V.; Mamedov, V. M.; Sidko, A. P.; Podkopaev, O. I.; Kravtsova, E. D.; Shimansky, A. F.
2017-06-01
Obtaining very high-purity germanium crystals with low dislocation density is a practically difficult problem, which requires knowledge and experience in growth processes. Dislocation density is one of the most important parameters defining the quality of germanium crystal. In this paper, we have performed experimental study of dislocation density during 4-in. germanium crystal growth using the Czochralski method and comprehensive unsteady modeling of the same crystal growth processes, taking into account global heat transfer, melt flow and melt/crystal interface shape evolution. Thermal stresses in the crystal and their relaxation with generation of dislocations within the Alexander-Haasen model have been calculated simultaneously with crystallization dynamics. Comparison to experimental data showed reasonable agreement for the temperature, interface shape and dislocation density in the crystal between calculation and experiment.
The Balance-of-Payments-Constrained Growth Model and the Limits to Export-Led Growth
Directory of Open Access Journals (Sweden)
Robert A. Blecker
2000-12-01
Full Text Available This paper discusses how A. P. Thirlwall's model of balance-of-payments-constrained growth can be adapted to analyze the idea of a "fallacy of composition" in the export-led growth strategy of many developing countries. The Deaton-Muellbauer model of the Almost Ideal Demand System (AIDS is used to represent the adding-up constraints on individual countries' exports, when they are all trying to export competing products to the same foreign markets (i.e. newly industrializing countries are exporting similar types of manufactured goods to the OECD countries. The relevance of the model to the recent financial crises in developing countries and policy alternatives for redirecting development strategies are also discussed.
Stochastic Differential Equation-Based Flexible Software Reliability Growth Model
Directory of Open Access Journals (Sweden)
P. K. Kapur
2009-01-01
Full Text Available Several software reliability growth models (SRGMs have been developed by software developers in tracking and measuring the growth of reliability. As the size of software system is large and the number of faults detected during the testing phase becomes large, so the change of the number of faults that are detected and removed through each debugging becomes sufficiently small compared with the initial fault content at the beginning of the testing phase. In such a situation, we can model the software fault detection process as a stochastic process with continuous state space. In this paper, we propose a new software reliability growth model based on Itô type of stochastic differential equation. We consider an SDE-based generalized Erlang model with logistic error detection function. The model is estimated and validated on real-life data sets cited in literature to show its flexibility. The proposed model integrated with the concept of stochastic differential equation performs comparatively better than the existing NHPP-based models.
Random-growth urban model with geographical fitness
Kii, Masanobu; Akimoto, Keigo; Doi, Kenji
2012-12-01
This paper formulates a random-growth urban model with a notion of geographical fitness. Using techniques of complex-network theory, we study our system as a type of preferential-attachment model with fitness, and we analyze its macro behavior to clarify the properties of the city-size distributions it predicts. First, restricting the geographical fitness to take positive values and using a continuum approach, we show that the city-size distributions predicted by our model asymptotically approach Pareto distributions with coefficients greater than unity. Then, allowing the geographical fitness to take negative values, we perform local coefficient analysis to show that the predicted city-size distributions can deviate from Pareto distributions, as is often observed in actual city-size distributions. As a result, the model we propose can generate a generic class of city-size distributions, including but not limited to Pareto distributions. For applications to city-population projections, our simple model requires randomness only when new cities are created, not during their subsequent growth. This property leads to smooth trajectories of city population growth, in contrast to other models using Gibrat’s law. In addition, a discrete form of our dynamical equations can be used to estimate past city populations based on present-day data; this fact allows quantitative assessment of the performance of our model. Further study is needed to determine appropriate formulas for the geographical fitness.
R.M. Solow Adjusted Model of Economic Growth
Directory of Open Access Journals (Sweden)
Ion Gh. Rosca
2007-05-01
Full Text Available Besides the models of M. Keynes, R.F. Harrod, E. Domar, D. Romer, Ramsey-Cass-Koopmans etc., the R.M. Solow model is part of the category which characterizes the economic growth. The paper proposes the study of the R.M. Solow adjusted model of economic growth, while the adjustment consisting in the model adaptation to the Romanian economic characteristics. The article is the first one from a three paper series dedicated to the macroeconomic modelling theme, using the R.M. Solow model, such as: “Measurement of the economic growth and extensions of the R.M. Solow adjusted model” and “Evolution scenarios at the Romanian economy level using the R.M. Solow adjusted model”. The analysis part of the model is based on the study of the equilibrium to the continuous case with some interpretations of the discreet one, by using the state diagram. The optimization problem at the economic level is also used; it is built up of a specified number of representative consumers and firms in order to reveal the interaction between these elements.
Cumulative growth of minor hysteresis loops in the Kolmogorov model
International Nuclear Information System (INIS)
Meilikhov, E. Z.; Farzetdinova, R. M.
2013-01-01
The phenomenon of nonrepeatability of successive remagnetization cycles in Co/M (M = Pt, Pd, Au) multilayer film structures is explained in the framework of the Kolmogorov crystallization model. It is shown that this model of phase transitions can be adapted so as to adequately describe the process of magnetic relaxation in the indicated systems with “memory.” For this purpose, it is necessary to introduce some additional elements into the model, in particular, (i) to take into account the fact that every cycle starts from a state “inherited” from the preceding cycle and (ii) to assume that the rate of growth of a new magnetic phase depends on the cycle number. This modified model provides a quite satisfactory qualitative and quantitative description of all features of successive magnetic relaxation cycles in the system under consideration, including the surprising phenomenon of cumulative growth of minor hysteresis loops.
Forecasting Costa Rican Quarterly Growth with Mixed-frequency Models
Directory of Open Access Journals (Sweden)
Adolfo Rodríguez Vargas
2014-11-01
Full Text Available We assess the utility of mixed-frequency models to forecast the quarterly growth rate of Costa Rican real GDP: we estimate bridge and MiDaS models with several lag lengths using information of the IMAE and compute forecasts (horizons of 0-4 quarters which are compared between themselves, with those of ARIMA models and with those resulting from forecast combinations. Combining the most accurate forecasts is most useful when forecasting in real time, whereas MiDaS forecasts are the best-performing overall: as the forecasting horizon increases, their precisionis affected relatively little; their success rates in predicting the direction of changes in the growth rate are stable, and several forecastsremain unbiased. In particular, forecasts computed from simple MiDaS with 9 and 12 lags are unbiased at all horizons and information sets assessed, and show the highest number of significant differences in forecasting ability in comparison with all other models.
Accounting for household heterogeneity in general equilibrium economic growth models
International Nuclear Information System (INIS)
Melnikov, N.B.; O'Neill, B.C.; Dalton, M.G.
2012-01-01
We describe and evaluate a new method of aggregating heterogeneous households that allows for the representation of changing demographic composition in a multi-sector economic growth model. The method is based on a utility and labor supply calibration that takes into account time variations in demographic characteristics of the population. We test the method using the Population-Environment-Technology (PET) model by comparing energy and emissions projections employing the aggregate representation of households to projections representing different household types explicitly. Results show that the difference between the two approaches in terms of total demand for energy and consumption goods is negligible for a wide range of model parameters. Our approach allows the effects of population aging, urbanization, and other forms of compositional change on energy demand and CO 2 emissions to be estimated and compared in a computationally manageable manner using a representative household under assumptions and functional forms that are standard in economic growth models.
Microstructural modelling of creep crack growth from a blunted crack
Onck, P.R.; Giessen, E. van der
1998-01-01
The effect of crack tip blunting on the initial stages of creep crack growth is investigated by means of a planar microstructural model in which grains are represented discretely. The actual linking-up process of discrete microcracks with the macroscopic crack is simulated, with full account of the
Escherichia coli growth modeling using neural network | Shamsudin ...
African Journals Online (AJOL)
technique that has the ability to predict with efficient and good performance. Using NARX, a highly accurate model was developed to predict the growth of Escherichia coli (E. coli) based on pH water parameter. The multiparameter portable sensor and spectrophotometer data were used to build and train the neural network.
A mean-field game economic growth model
Gomes, Diogo A.; Lafleche, Laurent; Nurbekyan, Levon
2016-01-01
Here, we examine a mean-field game (MFG) that models the economic growth of a population of non-cooperative, rational agents. In this MFG, agents are described by two state variables - the capital and consumer goods they own. Each agent seeks
Building Context with Tumor Growth Modeling Projects in Differential Equations
Beier, Julie C.; Gevertz, Jana L.; Howard, Keith E.
2015-01-01
The use of modeling projects serves to integrate, reinforce, and extend student knowledge. Here we present two projects related to tumor growth appropriate for a first course in differential equations. They illustrate the use of problem-based learning to reinforce and extend course content via a writing or research experience. Here we discuss…
A Role for M-Matrices in Modelling Population Growth
James, Glyn; Rumchev, Ventsi
2006-01-01
Adopting a discrete-time cohort-type model to represent the dynamics of a population, the problem of achieving a desired total size of the population under a balanced growth (contraction) and the problem of maintaining the desired size, once achieved, are studied. Properties of positive-time systems and M-matrices are used to develop the results,…
Models of Economic Growth and Development in the Context of ...
African Journals Online (AJOL)
The better-known models of economic growth such as the Lewis, Rostow,. Harrod-Domar ... produce highly educated populaces usually reap the benefits of such in terms of high per capita ..... The Russian revolution of 1917 led by Lenin proposed in theory a .... This was about government intervention into the economy to ...
Developmental trajectories of adolescent popularity: a growth curve modelling analysis.
Cillessen, Antonius H N; Borch, Casey
2006-12-01
Growth curve modelling was used to examine developmental trajectories of sociometric and perceived popularity across eight years in adolescence, and the effects of gender, overt aggression, and relational aggression on these trajectories. Participants were 303 initially popular students (167 girls, 136 boys) for whom sociometric data were available in Grades 5-12. The popularity and aggression constructs were stable but non-overlapping developmental dimensions. Growth curve models were run with SAS MIXED in the framework of the multilevel model for change [Singer, J. D., & Willett, J. B. (2003). Applied longitudinal data analysis. Oxford, UK: Oxford University Press]. Sociometric popularity showed a linear change trajectory; perceived popularity showed nonlinear change. Overt aggression predicted low sociometric popularity but an increase in perceived popularity in the second half of the study. Relational aggression predicted a decrease in sociometric popularity, especially for girls, and continued high-perceived popularity for both genders. The effect of relational aggression on perceived popularity was the strongest around the transition from middle to high school. The importance of growth curve models for understanding adolescent social development was discussed, as well as specific issues and challenges of growth curve analyses with sociometric data.
Hybrid discrete dislocation models for fatigue crack growth
Curtin, W. A.; Deshpande, V. S.; Needleman, A.; Van der Giessen, E.; Wallin, M.
A framework for accurately modeling fatigue crack growth in ductile crystalline solids is necessarily multiscale The creation of new free surface occurs at the atomistic scale, where the material's cohesive strength is controlled by the local chemistry On the other hand, significant dissipation
Growth and yield models for Eucalyptus grandis grown in Swaziland ...
African Journals Online (AJOL)
The aim of this study was to develop a stand-level growth and yield model for short-rotationEucalyptus grandis grown for pulp wood production at Piggs Peak in Swaziland. The data were derived from a Nelder 1a spacing trial established with E. grandis clonal cuttings in 1998 and terminated in 2005. Planting density ...
Modeling growth of specific spoilage organisms in tilapia ...
African Journals Online (AJOL)
Tilapia is an important aquatic fish, but severe spoilage of tilapia is most likely related to the global aquaculture. The spoilage is mostly caused by specific spoilage organisms (SSO). Therefore, it is very important to use microbial models to predict the growth of SSO in tilapia. This study firstly verified Pseudomonas and Vibrio ...
Studying historical occupational careers with multilevel growth models
Schulz, W.; Maas, I.
2010-01-01
In this article we propose to study occupational careers with historical data by using multilevel growth models. Historical career data are often characterized by a lack of information on the timing of occupational changes and by different numbers of observations of occupations per individual.
Modelling dimensional growth of three street tree species in the ...
African Journals Online (AJOL)
The results could also be used in the process of modelling energy use reduction, air pollution uptake, rainfall interception, carbon sequestration and microclimate modification of urban forests such as those found in the City of Tshwane. Keywords: allometry; regression; size relationships; tree growth; urban forests. Southern ...
Diameter growth performance of tree functional groups in Puerto Rican secondary tropical forests
Directory of Open Access Journals (Sweden)
Patricia Adame
2014-04-01
Full Text Available Aim of study: Understanding the factors that control tree growth in successional stands is particularly important for quantifying the carbon sequestration potential and timber yield of secondary tropical forests. Understanding the factors that control tree growth in successional stands is particularly important for quantifying the carbon sequestration potential and timber yield of secondary tropical forests. Yet, the high species diversity of mixed tropical forests, including many uncommon species, hinders the development of species-specific diameter growth models.Area of study: In these analyses, we grouped 82 species from secondary forests distributed across 93 permanent plots on the island of Puerto Rico.Material and Methods: Species were classified according to regeneration strategy and adult height into six functional groups. This classification allowed us to develop a robust diameter growth model using growth data collected from 1980-1990. We used mixed linear model regression to analyze tree diameter growth as a function of individual tree characteristics, stand structure, functional group and site factors.Main results: The proportion of variance in diameter growth explained by the model was 15.1%, ranging from 7.9 to 21.7%. Diameter at breast height, stem density and functional group were the most important predictors of tree growth in Puerto Rican secondary forest. Site factors such as soil and topography failed to predict diameter growth.Keywords: Caribbean forests; growth model; tropical forest succession; Puerto Rico.
Specific and General Human Capital in an Endogenous Growth Model
Evangelia Vourvachaki; Vahagn Jerbashian; : Sergey Slobodyan
2014-01-01
In this article, we define specific (general) human capital in terms of the occupations whose use is spread in a limited (wide) set of industries. We analyze the growth impact of an economy's composition of specific and general human capital, in a model where education and research and development are costly and complementary activities. The model suggests that a declining share of specific human capital, as observed in the Czech Republic, can be associated with a lower rate of long-term grow...
A Dynamic Growth Model for Flows of Foreign Direct Investment
Yi-Hui Chiang; Yiming Li; Chih-Young Hung
2007-01-01
In this work, we for the first time study the dynamic flows of the foreign direct investment (FDI) with a dynamic growth theory. We define the FDI flow as a process which transmits throughout a given social system by way of diverse communication channels. In model formulation, seven assumptions are thus proposed and the foreign capital policy of the host country is considered as an external influence; in addition, the investment policy of the investing country is modeled as an internal influe...
A Computable OLG Model for Gender and Growth Policy Analysis
Pierre-Richard Agénor
2012-01-01
This paper develops a computable Overlapping Generations (OLG) model for gender and growth policy analysis. The model accounts for human and physical capital accumulation (both public and private), intra- and inter-generational health persistence, fertility choices, and women's time allocation between market work, child rearing, and home production. Bargaining between spouses and gender bias, in the form of discrimination in the work place and mothers' time allocation between daughters and so...
Area Based Models of New Highway Route Growth
David Levinson; Wei Chen
2007-01-01
Empirical data and statistical models are used to answer the question of where new highway routes are most likely to be located. High-quality land-use, population distribution and highway network GIS data for the Twin CitiesMetropolitan Area from 1958 to 1990 are developed for this study. The highway system is classified into three levels, Interstate highways, divided highways, and secondary highways. Binary logit models estimate the new route growth probability of divided highways and second...
Probabilistic Model for Fatigue Crack Growth in Welded Bridge Details
DEFF Research Database (Denmark)
Toft, Henrik Stensgaard; Sørensen, John Dalsgaard; Yalamas, Thierry
2013-01-01
In the present paper a probabilistic model for fatigue crack growth in welded steel details in road bridges is presented. The probabilistic model takes the influence of bending stresses in the joints into account. The bending stresses can either be introduced by e.g. misalignment or redistribution...... of stresses in the structure. The fatigue stress ranges are estimated from traffic measurements and a generic bridge model. Based on the probabilistic models for the resistance and load the reliability is estimated for a typical welded steel detail. The results show that large misalignments in the joints can...
Model-independent cosmological constraints from growth and expansion
L'Huillier, Benjamin; Shafieloo, Arman; Kim, Hyungjin
2018-05-01
Reconstructing the expansion history of the Universe from Type Ia supernovae data, we fit the growth rate measurements and put model-independent constraints on some key cosmological parameters, namely, Ωm, γ, and σ8. The constraints are consistent with those from the concordance model within the framework of general relativity, but the current quality of the data is not sufficient to rule out modified gravity models. Adding the condition that dark energy density should be positive at all redshifts, independently of its equation of state, further constrains the parameters and interestingly supports the concordance model.
Stochastic modelling of avascular tumour growth and therapy
International Nuclear Information System (INIS)
Sahoo, S; Sahoo, A; Shearer, S F C
2011-01-01
In this paper, a generalized stochastic model for the growth of avascular tumours is presented. This model captures the dynamical evolution of avascular tumour cell subpopulations by incorporating Gaussian white noise into the growth rate of the mitotic function. This work generalizes the deterministic model proposed by Sherratt and Chaplain (2001 J. Math. Biol. 43 291) where they formulated a tumour model in an in vivo setting, in terms of continuum densities of proliferating, quiescent and necrotic cells. Detailed simulations of our model show that the inclusion of Gaussian noise in the original model of Sherratt and Chaplain substantially distorts the overall structure of the density profiles in addition to reducing the speed of tumour growth. Within this stochastic carcinogenesis framework the action of therapy is also investigated by replacing Gaussian white noise with a therapy term. We compare a constant therapy protocol with a logarithmic time-dependent protocol. Our results predict that a logarithmic therapy is more effective than the constant therapy protocol.
Modelling hair follicle growth dynamics as an excitable medium.
Directory of Open Access Journals (Sweden)
Philip J Murray
Full Text Available The hair follicle system represents a tractable model for the study of stem cell behaviour in regenerative adult epithelial tissue. However, although there are numerous spatial scales of observation (molecular, cellular, follicle and multi follicle, it is not yet clear what mechanisms underpin the follicle growth cycle. In this study we seek to address this problem by describing how the growth dynamics of a large population of follicles can be treated as a classical excitable medium. Defining caricature interactions at the molecular scale and treating a single follicle as a functional unit, a minimal model is proposed in which the follicle growth cycle is an emergent phenomenon. Expressions are derived, in terms of parameters representing molecular regulation, for the time spent in the different functional phases of the cycle, a formalism that allows the model to be directly compared with a previous cellular automaton model and experimental measurements made at the single follicle scale. A multi follicle model is constructed and numerical simulations are used to demonstrate excellent qualitative agreement with a range of experimental observations. Notably, the excitable medium equations exhibit a wider family of solutions than the previous work and we demonstrate how parameter changes representing altered molecular regulation can explain perturbed patterns in Wnt over-expression and BMP down-regulation mouse models. Further experimental scenarios that could be used to test the fundamental premise of the model are suggested. The key conclusion from our work is that positive and negative regulatory interactions between activators and inhibitors can give rise to a range of experimentally observed phenomena at the follicle and multi follicle spatial scales and, as such, could represent a core mechanism underlying hair follicle growth.
Continuum mathematical modelling of pathological growth of blood vessels
Stadnik, N. E.; Dats, E. P.
2018-04-01
The present study is devoted to the mathematical modelling of a human blood vessel pathological growth. The vessels are simulated as the thin-walled circular tube. The boundary value problem of the surface growth of an elastic thin-walled cylinder is solved. The analytical solution is obtained in terms of velocities of stress strain state parameters. The condition of thinness allows us to study finite displacements of cylinder surfaces by means of infinitesimal deformations. The stress-strain state characteristics, which depend on the mechanical parameters of the biological processes, are numerically computed and graphically analysed.
Sensitivity Analysis of a Riparian Vegetation Growth Model
Directory of Open Access Journals (Sweden)
Michael Nones
2016-11-01
Full Text Available The paper presents a sensitivity analysis of two main parameters used in a mathematic model able to evaluate the effects of changing hydrology on the growth of riparian vegetation along rivers and its effects on the cross-section width. Due to a lack of data in existing literature, in a past study the schematization proposed here was applied only to two large rivers, assuming steady conditions for the vegetational carrying capacity and coupling the vegetal model with a 1D description of the river morphology. In this paper, the limitation set by steady conditions is overcome, imposing the vegetational evolution dependent upon the initial plant population and the growth rate, which represents the potential growth of the overall vegetation along the watercourse. The sensitivity analysis shows that, regardless of the initial population density, the growth rate can be considered the main parameter defining the development of riparian vegetation, but it results site-specific effects, with significant differences for large and small rivers. Despite the numerous simplifications adopted and the small database analyzed, the comparison between measured and computed river widths shows a quite good capability of the model in representing the typical interactions between riparian vegetation and water flow occurring along watercourses. After a thorough calibration, the relatively simple structure of the code permits further developments and applications to a wide range of alluvial rivers.
A computer model for hydride blister growth in zirconium alloys
International Nuclear Information System (INIS)
White, A.J.; Sawatzky, A.; Woo, C.H.
1985-06-01
The failure of a Zircaloy-2 pressure tube in the Pickering unit 2 reactor started at a series of zirconium hydride blisters on the outside of the pressure tube. These blisters resulted from the thermal diffusion of hydrogen to the cooler regions of the pressure tube. In this report the physics of thermal diffusion of hydrogen in zirconium is reviewed and a computer model for blister growth in two-dimensional Cartesian geometry is described. The model is used to show that the blister-growth rate in a two-phase zirconium/zirconium-hydride region does not depend on the initial hydrogen concentration nor on the hydrogen pick-up rate, and that for a fixed far-field temperature there is an optimum pressure-type/calandria-tube contact temperature for growing blisters. The model described here can also be used to study large-scale effects, such as hydrogen-depletion zones around hydride blisters
A Big Bang model of human colorectal tumor growth.
Sottoriva, Andrea; Kang, Haeyoun; Ma, Zhicheng; Graham, Trevor A; Salomon, Matthew P; Zhao, Junsong; Marjoram, Paul; Siegmund, Kimberly; Press, Michael F; Shibata, Darryl; Curtis, Christina
2015-03-01
What happens in early, still undetectable human malignancies is unknown because direct observations are impractical. Here we present and validate a 'Big Bang' model, whereby tumors grow predominantly as a single expansion producing numerous intermixed subclones that are not subject to stringent selection and where both public (clonal) and most detectable private (subclonal) alterations arise early during growth. Genomic profiling of 349 individual glands from 15 colorectal tumors showed an absence of selective sweeps, uniformly high intratumoral heterogeneity (ITH) and subclone mixing in distant regions, as postulated by our model. We also verified the prediction that most detectable ITH originates from early private alterations and not from later clonal expansions, thus exposing the profile of the primordial tumor. Moreover, some tumors appear 'born to be bad', with subclone mixing indicative of early malignant potential. This new model provides a quantitative framework to interpret tumor growth dynamics and the origins of ITH, with important clinical implications.
Bifurcation analysis of a delayed mathematical model for tumor growth
International Nuclear Information System (INIS)
Khajanchi, Subhas
2015-01-01
In this study, we present a modified mathematical model of tumor growth by introducing discrete time delay in interaction terms. The model describes the interaction between tumor cells, healthy tissue cells (host cells) and immune effector cells. The goal of this study is to obtain a better compatibility with reality for which we introduced the discrete time delay in the interaction between tumor cells and host cells. We investigate the local stability of the non-negative equilibria and the existence of Hopf-bifurcation by considering the discrete time delay as a bifurcation parameter. We estimate the length of delay to preserve the stability of bifurcating periodic solutions, which gives an idea about the mode of action for controlling oscillations in the tumor growth. Numerical simulations of the model confirm the analytical findings
DEFF Research Database (Denmark)
Mejlholm, Ole; Dalgaard, Paw
2013-01-01
A new and extensive growth and growth boundary model for psychrotolerant Lactobacillus spp. was developed and validated for processed and unprocessed products of seafood and meat. The new model was developed by refitting and expanding an existing cardinal parameter model for growth and the growth...... of psychrotolerant Lactobacillus spp. was clearly demonstrated. The new model can be used to predict growth of psychrotolerant Lactobacillus spp. in seafood and meat products e.g. prediction of the time to a critical cell concentration of bacteria is considered useful for establishing the shelf life. In addition...... boundary of lactic acid bacteria (LAB) in processed seafood (O. Mejlholm and P. Dalgaard, J. Food Prot. 70. 2485–2497, 2007). Initially, to estimate values for the maximum specific growth rate at the reference temperature of 25°C (μref) and the theoretical minimum temperature that prevents growth...
Net energy analysis in a Ramsey–Hotelling growth model
International Nuclear Information System (INIS)
Macías, Arturo; Matilla-García, Mariano
2015-01-01
This article presents a dynamic growth model with energy as an input in the production function. The available stock of energy resources is ordered by a quality parameter based on energy accounting: the “Energy Return on Energy Invested” (EROI). In our knowledge this is the first paper where EROI fits in a neoclassical growth model (with individual utility maximization and market equilibrium), establishing the economic use of “net energy analysis” on a firmer theoretical ground. All necessary concepts to link neoclassical economics and EROI are discussed before their use in the model, and a comparative static analysis of the steady states of a simplified version of the model is presented. - Highlights: • A neoclassical growth model with EROI (“Energy Return on Energy Invested”) is shown • All concepts linking neoclassical economics and net energy analysis are discussed • Any EROI decline can be compensated increasing gross activity in the energy sector. • The economic impact of EROI depends on some non-energy cost in the energy sector. • Comparative steady-state statics for different EROI levels is performed and discussed. • Policy implications are suggested.
Predicting Madura cattle growth curve using non-linear model
Widyas, N.; Prastowo, S.; Widi, T. S. M.; Baliarti, E.
2018-03-01
Madura cattle is Indonesian native. It is a composite breed that has undergone hundreds of years of selection and domestication to reach nowadays remarkable uniformity. Crossbreeding has reached the isle of Madura and the Madrasin, a cross between Madura cows and Limousine semen emerged. This paper aimed to compare the growth curve between Madrasin and one type of pure Madura cows, the common Madura cattle (Madura) using non-linear models. Madura cattles are kept traditionally thus reliable records are hardly available. Data were collected from small holder farmers in Madura. Cows from different age classes (5years) were observed, and body measurements (chest girth, body length and wither height) were taken. In total 63 Madura and 120 Madrasin records obtained. Linear model was built with cattle sub-populations and age as explanatory variables. Body weights were estimated based on the chest girth. Growth curves were built using logistic regression. Results showed that within the same age, Madrasin has significantly larger body compared to Madura (plogistic models fit better for Madura and Madrasin cattle data; with the estimated MSE for these models were 39.09 and 759.28 with prediction accuracy of 99 and 92% for Madura and Madrasin, respectively. Prediction of growth curve using logistic regression model performed well in both types of Madura cattle. However, attempts to administer accurate data on Madura cattle are necessary to better characterize and study these cattle.
Developing a dynamic growth model for teak plantations in India
Directory of Open Access Journals (Sweden)
Vindhya Prasad Tewari
2014-05-01
Full Text Available Background Tectona grandis (teak is one of the most important tropical timber speciesoccurring naturally in India. Appropriate growth models, based on advanced modeling techniques,are not available but are necessary for the successful management of teak stands in the country.Long-term forest planning requires mathematical models, and the principles of Dynamical SystemTheory provide a solid foundation for these. Methods The state-space approach makes it possible to accommodate disturbances and avarying environment. In this paper, an attempt has been made to develop a dynamic growthmodel based on the limited data, consisting of three annual measurements, collected from 22 teak sample plots in Karnataka, Southern India. Results A biologically consistent whole-stand growth model has been presented which uses thestate-space approach for modelling rates of change of three state-variables viz., dominant height,stems per hectare and stand basal area. Moreover, the model includes a stand volume equationas an output function to estimate this variable at any point in time. Transition functions werefitted separately and simultaneously. Moreover, a continuous autoregressive error structure isalso included in the modelling process. For fitting volume equation, generalized method of moments was used to get efficient parameter estimates under heteroscedastic conditions. Conclusions A simple model containing few free parameters performed well and is particularlywell suited to situations where available data is scarce.
Modelling the interaction between flooding events and economic growth
Directory of Open Access Journals (Sweden)
J. Grames
2015-06-01
Full Text Available Socio-hydrology describes the interaction between the socio-economy and water. Recent models analyze the interplay of community risk-coping culture, flooding damage and economic growth (Di Baldassarre et al., 2013; Viglione et al., 2014. These models descriptively explain the feedbacks between socio-economic development and natural disasters like floods. Contrary to these descriptive models, our approach develops an optimization model, where the intertemporal decision of an economic agent interacts with the hydrological system. In order to build this first economic growth model describing the interaction between the consumption and investment decisions of an economic agent and the occurrence of flooding events, we transform an existing descriptive stochastic model into an optimal deterministic model. The intermediate step is to formulate and simulate a descriptive deterministic model. We develop a periodic water function to approximate the former discrete stochastic time series of rainfall events. Due to the non-autonomous exogenous periodic rainfall function the long-term path of consumption and investment will be periodic.
The impact of the British model on economic growth
Directory of Open Access Journals (Sweden)
Simon György Jr.
2007-01-01
Full Text Available The paper is searching for an answer to the question how the British model affected economic development in its mother country, the United Kingdom. The statistical analysis, models of mathematical economics and econometric investigation make it probable to conclude that there was a substantial difference in success between the Thatcherite and the Blairite economic policies; the latter proved more effective. It is particularly remarkable that the Blairite model, connecting privatization with a successful employment policy, reduced unemployment and social sensitivity, has not only speeded up economic growth but also improved economic equilibrium, curtailing, among others, the budget deficit.
Catalyst design for carbon nanotube growth using atomistic modeling
International Nuclear Information System (INIS)
Pint, Cary L; Bozzolo, Guillermo; Hauge, Robert
2008-01-01
The formation and stability of bimetallic catalyst particles, in the framework of carbon nanotube growth, is studied using the Bozzolo-Ferrante-Smith (BFS) method for alloys. Monte Carlo-Metropolis simulations with the BFS method are utilized in order to predict and study equilibrium configurations for nanoscale catalyst particles which are directly relevant to the catalyst state prior to growth of carbon nanotubes. At the forefront of possible catalyst combinations is the popular Fe-Mo bimetallic catalyst, which we have recently studied experimentally. We explain our experimental results, which indicate that the growth observed is dependent on the order of co-catalyst deposition, in the straightforward interpretation of BFS strain and chemical energy contributions toward the formation of Fe-Mo catalyst prior to growth. We find that the competition between the formation of metastable inner Mo cores and clusters of surface-segregated Mo atoms in Fe-Mo catalyst particles influences catalyst formation, and we investigate the role of Mo concentration and catalyst particle size in this process. Finally, we apply the same modeling approach to other prominent bimetallic catalysts and suggest that this technique can be a powerful tool to understand and manipulate catalyst design for highly efficient carbon nanotube growth
Growth of the modeling of Escherichia coli in milk
International Nuclear Information System (INIS)
Mbangu, N.; Malakasa, M.; Ekalakala, T.; N'dendje, B.; Abedi, M.; Muzembe, K.; Bandejile, M.
2010-01-01
Escherichia coli is a contaminant potential of milk. Collective toxinfections implying the bacterium and milk were announced of share the world. However, no identified work proposed a mathematical expression of the growth of the bacterium in milk. The interest of such a step is however undeniable. Under specified conditions, the mathematical formulation of the growth provides the means of considering the population bacterial when the analyses cannot be carried out. It also makes it possible to test the negatiable instruments of the unfavourable circumstances supposed suchas chain breakage of cold on the development of the microbial charge. This work established mathematical expressions of the growth of Escherichia coli in milk for part of its range of temperature of growth suboptimale i.e. between 25 and 35 Deg C. It was not possible to generalize these expressions for predictions on all the range of temperature suboptimal. This work also made it possible to highlight a deviation of the behavoir of the bacterium compared to the model of Ratkowsky without however that it is not possible to provide a univocal explanantion of it. Varoius assumptions were put forth referring to either a singularity of the behavior of the bacterium or a skew of the value of its minimal temperature of growth
Growth Modeling of Human Mandibles using Non-Euclidean Metrics
DEFF Research Database (Denmark)
Hilger, Klaus Baggesen; Larsen, Rasmus; Wrobel, Mark
2003-01-01
From a set of 31 three-dimensional CT scans we model the temporal shape and size of the human mandible. Each anatomical structure is represented using 14851 semi-landmarks, and mapped into Procrustes tangent space. Exploratory subspace analyses are performed leading to linear models of mandible...... shape evolution in Procrustes space. The traditional variance analysis results in a one-dimensional growth model. However, working in a non-Euclidean metric results in a multimodal model with uncorrelated modes of biological variation. The applied non-Euclidean metric is governed by the correlation...... structure of the estimated noise in the data. The generative models are compared, and evaluated on the basis of a cross validation study. The new non-Euclidean analysis is completely data driven. It not only gives comparable results w.r.t. to previous studies of the mean modelling error, but in addition...
Evolutionary model of the growth and size of firms
Kaldasch, Joachim
2012-07-01
The key idea of this model is that firms are the result of an evolutionary process. Based on demand and supply considerations the evolutionary model presented here derives explicitly Gibrat's law of proportionate effects as the result of the competition between products. Applying a preferential attachment mechanism for firms, the theory allows to establish the size distribution of products and firms. Also established are the growth rate and price distribution of consumer goods. Taking into account the characteristic property of human activities to occur in bursts, the model allows also an explanation of the size-variance relationship of the growth rate distribution of products and firms. Further the product life cycle, the learning (experience) curve and the market size in terms of the mean number of firms that can survive in a market are derived. The model also suggests the existence of an invariant of a market as the ratio of total profit to total revenue. The relationship between a neo-classic and an evolutionary view of a market is discussed. The comparison with empirical investigations suggests that the theory is able to describe the main stylized facts concerning the size and growth of firms.
Orchestrated structure evolution: modeling growth-regulated nanomanufacturing
Energy Technology Data Exchange (ETDEWEB)
Abbasi, Shaghayegh; Boehringer, Karl F [Department of Electrical Engineering, University of Washington, Seattle, WA 98195-2500 (United States); Kitayaporn, Sathana; Schwartz, Daniel T, E-mail: karlb@washington.edu [Department of Chemical Engineering, University of Washington, Seattle, WA 98195-2500 (United States)
2011-04-22
Orchestrated structure evolution (OSE) is a scalable manufacturing method that combines the advantages of top-down (tool-directed) and bottom-up (self-propagating) approaches. The method consists of a seed patterning step that defines where material nucleates, followed by a growth step that merges seeded islands into the final patterned thin film. We develop a model to predict the completed pattern based on a computationally efficient approximate Green's function solution of the diffusion equation plus a Voronoi diagram based approach that defines the final grain boundary structure. Experimental results rely on electron beam lithography to pattern the seeds, followed by the mass transfer limited growth of copper via electrodeposition. The seed growth model is compared with experimental results to quantify nearest neighbor seed-to-seed interactions as well as how seeds interact with the pattern boundary to impact the local growth rate. Seed-to-seed and seed-to-pattern interactions are shown to result in overgrowth of seeds on edges and corners of the shape, where seeds have fewer neighbors. We explore how local changes to the seed location can be used to improve the patterning quality without increasing the manufacturing cost. OSE is shown to enable a unique set of trade-offs between the cost, time, and quality of thin film patterning.
Correcting Model Fit Criteria for Small Sample Latent Growth Models with Incomplete Data
McNeish, Daniel; Harring, Jeffrey R.
2017-01-01
To date, small sample problems with latent growth models (LGMs) have not received the amount of attention in the literature as related mixed-effect models (MEMs). Although many models can be interchangeably framed as a LGM or a MEM, LGMs uniquely provide criteria to assess global data-model fit. However, previous studies have demonstrated poor…
On the growth and dissemination laws in a mathematical model of metastatic growth
Directory of Open Access Journals (Sweden)
Benzekry Sébastien
2015-01-01
Full Text Available Metastasis represents one of the main clinical challenge in cancer treatment since it is associated with the majority of deaths. Recent technological advances allow quantification of the dynamics of the process by means of noninvasive techniques such as longitudinal tracking of bioluminescent cells. The metastatic process was simplified here into two essential components – dissemination and colonization – which were mathematically formalized in terms of simple quantitative laws. The resulting mathematical model was confronted to in vivo experimental data of spontaneous metastasis after primary tumor resection. We discuss how much information can be inferred from confrontation of theories to the data with emphasis on identifiability issues. It is shown that two mutually exclusive assumptions for the secondary growth law (namely same or different from the primary tumor growth law could fit equally well the data. Similarly, the fractal dimension coeffcient in the dissemination law could not be uniquely determined from data on total metastatic burden only. Together, these results delimitate the range of information that can be recovered from fitting data of metastatic growth to already simplified mathematical models.
Mathematical modeling and numerical simulation of Czochralski Crystal Growth
Energy Technology Data Exchange (ETDEWEB)
Jaervinen, J.; Nieminen, R. [Center for Scientific Computing, Espoo (Finland)
1996-12-31
A detailed mathematical model and numerical simulation tools based on the SUPG Finite Element Method for the Czochralski crystal growth has been developed. In this presentation the mathematical modeling and numerical simulation of the melt flow and the temperature distribution in a rotationally symmetric crystal growth environment is investigated. The temperature distribution and the position of the free boundary between the solid and liquid phases are solved by using the Enthalpy method. Heat inside of the Czochralski furnace is transferred by radiation, conduction and convection. The melt flow is governed by the incompressible Navier-Stokes equations coupled with the enthalpy equation. The melt flow is numerically demonstrated and the temperature distribution in the whole Czochralski furnace. (author)
Mathematical modeling and numerical simulation of Czochralski Crystal Growth
Energy Technology Data Exchange (ETDEWEB)
Jaervinen, J; Nieminen, R [Center for Scientific Computing, Espoo (Finland)
1997-12-31
A detailed mathematical model and numerical simulation tools based on the SUPG Finite Element Method for the Czochralski crystal growth has been developed. In this presentation the mathematical modeling and numerical simulation of the melt flow and the temperature distribution in a rotationally symmetric crystal growth environment is investigated. The temperature distribution and the position of the free boundary between the solid and liquid phases are solved by using the Enthalpy method. Heat inside of the Czochralski furnace is transferred by radiation, conduction and convection. The melt flow is governed by the incompressible Navier-Stokes equations coupled with the enthalpy equation. The melt flow is numerically demonstrated and the temperature distribution in the whole Czochralski furnace. (author)
Zavala, Miguel A; Angulo, Oscar; Bravo de la Parra, Rafael; López-Marcos, Juan C
2007-02-07
Light competition and interspecific differences in shade tolerance are considered key determinants of forest stand structure and dynamics. Specifically two main stand diameter distribution types as a function of shade tolerance have been proposed based on empirical observations. All-aged stands of shade tolerant species tend to have steeply descending, monotonic diameter distributions (inverse J-shaped curves). Shade intolerant species in contrast typically exhibit normal (unimodal) tree diameter distributions due to high mortality rates of smaller suppressed trees. In this study we explore the generality of this hypothesis which implies a causal relationship between light competition or shade tolerance and stand structure. For this purpose we formulate a partial differential equation system of stand dynamics as a function of individual tree growth, recruitment and mortality which allows us to explore possible individual-based mechanisms--e.g. light competition-underlying observed patterns of stand structure--e.g. unimodal or inverse J-shaped equilibrium diameter curves. We find that contrary to expectations interspecific differences in growth patterns can result alone in any of the two diameter distributions types observed in the field. In particular, slow growing species can present unimodal equilibrium curves even in the absence of light competition. Moreover, light competition and shade intolerance evaluated both at the tree growth and mortality stages did not have a significant impact on stand structure that tended to converge systematically towards an inverse J-shaped curves for most tree growth scenarios. Realistic transient stand dynamics for even aged stands of shade intolerant species (unimodal curves) were only obtained when recruitment was completely suppressed, providing further evidence on the critical role played by juvenile stages of tree development (e.g. the sampling stage) on final forest structure and composition. The results also point out the
BUILDING NEW BUSINESS MODELS FOR SUSTAINABLE GROWTH AND DEVELOPMENT
Taco C. R. van Someren; Shuhua van Someren-Wang
2011-01-01
Considered are issues of methodology and methods, as well as ideology of strategic innovation. Using the tools of this approach is offered as mechanisms to develop and build business models for sustainable socio-economic economic growth and development of different regions. The connection between key problems of sustainable development and management policy of different economic entities is studied. The consultancy company Ynnovate’s experience in addressing these issues in the EU and China i...
A simple model of discontinuous firm’s growth
D'Elia, Enrico
2011-01-01
Typically, firms change their size through a row of discrete leaps over time. Sunk costs, regulatory, financial and organizational constraints, talent distribution and other factors may explain this fact. However, firms tend to grow or fall discontinuously even if those inertial factors were removed. For instance, a very essential model of discontinuous growth can be based on a couple of assumptions concerning only technology and entrepreneurs’ strategy, that is: (a) in the short run, the...
Modeling of growth and laccase production by Pycnoporus sanguineus.
Saat, Muhammad Naziz; Annuar, Mohamad Suffian Mohamad; Alias, Zazali; Chuan, Ling Tau; Chisti, Yusuf
2014-05-01
Production of extracellular laccase by the white-rot fungus Pycnoporus sanguineus was examined in batch submerged cultures in shake flasks, baffled shake flasks and a stirred tank bioreactor. The biomass growth in the various culture systems closely followed a logistic growth model. The production of laccase followed a Luedeking-Piret model. A modified Luedeking-Piret model incorporating logistic growth effectively described the consumption of glucose. Biomass productivity, enzyme productivity and substrate consumption were enhanced in baffled shake flasks relative to the cases for the conventional shake flasks. This was associated with improved oxygen transfer in the presence of the baffles. The best results were obtained in the stirred tank bioreactor. At 28 °C, pH 4.5, an agitation speed of 600 rpm and a dissolved oxygen concentration of ~25 % of air saturation, the laccase productivity in the bioreactor exceeded 19 U L(-1 )days(-1), or 1.5-fold better than the best case for the baffled shake flask. The final concentration of the enzyme was about 325 U L(-1).
Crystal plasticity modeling of irradiation growth in Zircaloy-2
Patra, Anirban; Tomé, Carlos N.; Golubov, Stanislav I.
2017-08-01
A physically based reaction-diffusion model is implemented in the visco-plastic self-consistent (VPSC) crystal plasticity framework to simulate irradiation growth in hcp Zr and its alloys. The reaction-diffusion model accounts for the defects produced by the cascade of displaced atoms, their diffusion to lattice sinks and the contribution to crystallographic strain at the level of single crystals. The VPSC framework accounts for intergranular interactions and irradiation creep, and calculates the strain in the polycrystalline ensemble. A novel scheme is proposed to model the simultaneous evolution of both, number density and radius, of irradiation-induced dislocation loops directly from experimental data of dislocation density evolution during irradiation. This framework is used to predict the irradiation growth behaviour of cold-worked Zircaloy-2 and trends compared to available experimental data. The role of internal stresses in inducing irradiation creep is discussed. Effects of grain size, texture and external stress on the coupled irradiation growth and creep behaviour are also studied and compared with available experimental data.
Software reliability growth models with normal failure time distributions
International Nuclear Information System (INIS)
Okamura, Hiroyuki; Dohi, Tadashi; Osaki, Shunji
2013-01-01
This paper proposes software reliability growth models (SRGM) where the software failure time follows a normal distribution. The proposed model is mathematically tractable and has sufficient ability of fitting to the software failure data. In particular, we consider the parameter estimation algorithm for the SRGM with normal distribution. The developed algorithm is based on an EM (expectation-maximization) algorithm and is quite simple for implementation as software application. Numerical experiment is devoted to investigating the fitting ability of the SRGMs with normal distribution through 16 types of failure time data collected in real software projects
A new growth model for the Russian economy1
Directory of Open Access Journals (Sweden)
Alexey Kudrin
2015-03-01
Full Text Available The problems underlying the current slowdown of the Russian economy are of a persistent nature and cannot be resolved with simple measures such as a softer monetary or fiscal policy. The fundamen- tal reason for these problems is the weak market environment dominated by public and quasi-public companies. A new growth model should be based upon strong incentive for the business, as well as the government regulation system, to improve efficiency. This article defines the main steps to be taken in building such a model.
John R. Jones; George A. Schier
1985-01-01
This chapter considers aspen growth as a process, and discusses some characteristics of the growth and development of trees and stands. For the most part, factors affecting growth are discussed elsewhere, particularly in the GENETICS AND VARIATION chapter and in chapters in PART 11. ECOLOGY. Aspen growth as it relates to wood production is examined in the WOOD RESOURCE...
Models of lipid droplets growth and fission in adipocyte cells
Energy Technology Data Exchange (ETDEWEB)
Boschi, Federico, E-mail: federico.boschi@univr.it [Department of Computer Science, University of Verona, Strada Le Grazie 15, 37134 Verona (Italy); Rizzatti, Vanni; Zamboni, Mauro [Department of Medicine, Geriatric Section, University of Verona, Piazzale Stefani 1, 37126 Verona (Italy); Sbarbati, Andrea [Department of Neurological and Movement Sciences, University of Verona, Strada Le Grazie 8, 37134 Verona (Italy)
2015-08-15
catabolism (fission and the decrease through neutral lipid exit from pre-existing droplets) to reproduce their size reduction observed in lipolytic conditions. The results suggest that each single process, considered alone, can not be considered the only responsible for the size variation observed, but more than one of them, playing together, can quite well reproduce the experimental data. - Highlights: The growth and fission of the lipid droplets (LDs) were computationally simulated. To write and test the growth and fission models more than 110,000 LDs were measured. The usual processes considered alone, are not able to justify the experimental data. Some processes, playing together, can explain the growth and fission.
Models of lipid droplets growth and fission in adipocyte cells
International Nuclear Information System (INIS)
Boschi, Federico; Rizzatti, Vanni; Zamboni, Mauro; Sbarbati, Andrea
2015-01-01
catabolism (fission and the decrease through neutral lipid exit from pre-existing droplets) to reproduce their size reduction observed in lipolytic conditions. The results suggest that each single process, considered alone, can not be considered the only responsible for the size variation observed, but more than one of them, playing together, can quite well reproduce the experimental data. - Highlights: The growth and fission of the lipid droplets (LDs) were computationally simulated. To write and test the growth and fission models more than 110,000 LDs were measured. The usual processes considered alone, are not able to justify the experimental data. Some processes, playing together, can explain the growth and fission
A sharp interface model for void growth in irradiated materials
Hochrainer, Thomas; El-Azab, Anter
2015-03-01
A thermodynamic formalism for the interaction of point defects with free surfaces in single-component solids has been developed and applied to the problem of void growth by absorption of point defects in irradiated metals. This formalism consists of two parts, a detailed description of the dynamics of defects within the non-equilibrium thermodynamic frame, and the application of the second law of thermodynamics to provide closure relations for all kinetic equations. Enforcing the principle of non-negative entropy production showed that the description of the problem of void evolution under irradiation must include a relationship between the normal fluxes of defects into the void surface and the driving thermodynamic forces for the void surface motion; these thermodynamic forces are identified for both vacancies and interstitials and the relationships between these forces and the normal point defect fluxes are established using the concepts of transition state theory. The latter theory implies that the defect accommodation into the surface is a thermally activated process. Numerical examples are given to illustrate void growth dynamics in this new formalism and to investigate the effect of the surface energy barriers on void growth. Consequences for phase field models of void growth are discussed.
Persistent G. lamblia impairs growth in a murine malnutrition model.
Bartelt, Luther A; Roche, James; Kolling, Glynis; Bolick, David; Noronha, Francisco; Naylor, Caitlin; Hoffman, Paul; Warren, Cirle; Singer, Steven; Guerrant, Richard
2013-06-01
Giardia lamblia infections are nearly universal among children in low-income countries and are syndemic with the triumvirate of malnutrition, diarrhea, and developmental growth delays. Amidst the morass of early childhood enteropathogen exposures in these populations, G. lamblia–specific associations with persistent diarrhea, cognitive deficits, stunting, and nutrient deficiencies have demonstrated conflicting results, placing endemic pediatric giardiasis in a state of equipoise. Many infections in endemic settings appear to be asymptomatic/ subclinical, further contributing to uncertainty regarding a causal link between G. lamblia infection and developmental delay. We used G. lamblia H3 cyst infection in a weaned mouse model of malnutrition to demonstrate that persistent giardiasis leads to epithelial cell apoptosis and crypt hyperplasia. Infection was associated with a Th2-biased inflammatory response and impaired growth. Malnutrition accentuated the severity of these growth decrements. Faltering malnourished mice exhibited impaired compensatory responses following infection and demonstrated an absence of crypt hyperplasia and subsequently blunted villus architecture. Concomitantly, severe malnutrition prevented increases in B220+ cells in the lamina propria as well as mucosal Il4 and Il5 mRNA in response to infection. These findings add insight into the potential role of G. lamblia as a "stunting" pathogen and suggest that, similarly, malnourished children may be at increased risk of G. lamblia– potentiated growth decrements.
Modeling Conformal Growth in Photonic Crystals and Comparing to Experiment
Brzezinski, Andrew; Chen, Ying-Chieh; Wiltzius, Pierre; Braun, Paul
2008-03-01
Conformal growth, e.g. atomic layer deposition (ALD), of materials such as silicon and TiO2 on three dimensional (3D) templates is important for making photonic crystals. However, reliable calculations of optical properties as a function of the conformal growth, such as the optical band structure, are hampered by difficultly in accurately assessing a deposited material's spatial distribution. A widely used approximation ignores ``pinch off'' of precursor gas and assumes complete template infilling. Another approximation results in non-uniform growth velocity by employing iso-intensity surfaces of the 3D interference pattern used to create the template. We have developed an accurate model of conformal growth in arbitrary 3D periodic structures, allowing for arbitrary surface orientation. Results are compared with the above approximations and with experimentally fabricated photonic crystals. We use an SU8 polymer template created by 4-beam interference lithography, onto which various amounts of TiO2 are grown by ALD. Characterization is performed by analysis of cross-sectional scanning electron micrographs and by solid angle resolved optical spectroscopy.
Directory of Open Access Journals (Sweden)
Wei-Bin Zhang
2016-09-01
Full Text Available The study builds a model of dynamic interactions between the birth rate, the mortality rate, the population, wealth accumulation, time distribution between work, leisure and children caring, habit formation and preference change. The production technology and markets are built on the Solow growth model. We base our modeling the population dynamics on the Haavelmo population model and the Barro-Becker fertility choice model. This study takes account of habit formation and preference change. Although it is influenced by the Ramsey growth theory with time preference and habit formation, it uses Zhang’s approach to the household with habit formation and preference change. We synthesize different dynamic forces in a compact framework, using the utility function proposed by Zhang. Analytically, we focus on transitional processes as well as economic equilibrium. As the economic system is given by autonomous nonlinear differential equations, it is not easy to analyze its behavior. We simulate the model to demonstrate the existence of an equilibrium point and plot the motion of the dynamic system. We examine the effects of changes in weights given to the habit stock of children, the wife’s wage rate having negative impact on the propensity to have children, the wife weighing less the habit stock of leisure time, the wife’s habit stock of leisure time having negative impact on the husband’s propensity to use leisure time, the wife’s wage rate having negative impact on the husband’s propensity to use leisure time, woman’s human capital being improved, a rise in the total factor productivity, and the mother spending more time on each child fostering.
Multiphase modelling of vascular tumour growth in two spatial dimensions
Hubbard, M.E.
2013-01-01
In this paper we present a continuum mathematical model of vascular tumour growth which is based on a multiphase framework in which the tissue is decomposed into four distinct phases and the principles of conservation of mass and momentum are applied to the normal/healthy cells, tumour cells, blood vessels and extracellular material. The inclusion of a diffusible nutrient, supplied by the blood vessels, allows the vasculature to have a nonlocal influence on the other phases. Two-dimensional computational simulations are carried out on unstructured, triangular meshes to allow a natural treatment of irregular geometries, and the tumour boundary is captured as a diffuse interface on this mesh, thereby obviating the need to explicitly track the (potentially highly irregular and ill-defined) tumour boundary. A hybrid finite volume/finite element algorithm is used to discretise the continuum model: the application of a conservative, upwind, finite volume scheme to the hyperbolic mass balance equations and a finite element scheme with a stable element pair to the generalised Stokes equations derived from momentum balance, leads to a robust algorithm which does not use any form of artificial stabilisation. The use of a matrix-free Newton iteration with a finite element scheme for the nutrient reaction-diffusion equations allows full nonlinearity in the source terms of the mathematical model.Numerical simulations reveal that this four-phase model reproduces the characteristic pattern of tumour growth in which a necrotic core forms behind an expanding rim of well-vascularised proliferating tumour cells. The simulations consistently predict linear tumour growth rates. The dependence of both the speed with which the tumour grows and the irregularity of the invading tumour front on the model parameters is investigated. © 2012 Elsevier Ltd.
Interfacial properties in a discrete model for tumor growth
Moglia, Belén; Guisoni, Nara; Albano, Ezequiel V.
2013-03-01
We propose and study, by means of Monte Carlo numerical simulations, a minimal discrete model for avascular tumor growth, which can also be applied for the description of cell cultures in vitro. The interface of the tumor is self-affine and its width can be characterized by the following exponents: (i) the growth exponent β=0.32(2) that governs the early time regime, (ii) the roughness exponent α=0.49(2) related to the fluctuations in the stationary regime, and (iii) the dynamic exponent z=α/β≃1.49(2), which measures the propagation of correlations in the direction parallel to the interface, e.g., ξ∝t1/z, where ξ is the parallel correlation length. Therefore, the interface belongs to the Kardar-Parisi-Zhang universality class, in agreement with recent experiments of cell cultures in vitro. Furthermore, density profiles of the growing cells are rationalized in terms of traveling waves that are solutions of the Fisher-Kolmogorov equation. In this way, we achieved excellent agreement between the simulation results of the discrete model and the continuous description of the growth front of the culture or tumor.
Balanced growth path solutions of a Boltzmann mean field game model for knowledge growth
Burger, Martin; Lorz, Alexander; Wolfram, Marie Therese
2016-01-01
events or by producing goods with the knowledge they already have. The existence of balanced growth path solutions implies exponential growth of the overall production in time. We prove existence of balanced growth path solutions if the initial
Modeling Growth and Yield of Schizolobium amazonicum under Different Spacings
Directory of Open Access Journals (Sweden)
Gilson Fernandes da Silva
2013-01-01
Full Text Available This study aimed to present an approach to model the growth and yield of the species Schizolobium amazonicum (Paricá based on a study of different spacings located in Pará, Brazil. Whole-stand models were employed, and two modeling strategies (Strategies A and B were tested. Moreover, the following three scenarios were evaluated to assess the accuracy of the model in estimating total and commercial volumes at five years of age: complete absence of data (S1; available information about the variables basal area, site index, dominant height, and number of trees at two years of age (S2; and this information available at five years of age (S3. The results indicated that the 3 × 2 spacing has a higher mortality rate than normal, and, in general, greater spacing corresponds to larger diameter and average height and smaller basal area and volume per hectare. In estimating the total and commercial volumes for the three scenarios tested, Strategy B seems to be the most appropriate method to estimate the growth and yield of Paricá plantations in the study region, particularly because Strategy A showed a significant bias in its estimates.
Growth fluctuations in a class of deposition models
Balazs, M
2003-01-01
We compute the growth fluctuations in equilibrium of a wide class of deposition models. These models also serve as general frame to several nearest-neighbor particle jump processes, e.g. the simple exclusion or the zero range process, where our result turns to current fluctuations of the particles. We use martingale technique and coupling methods to show that, rescaled by time, the variance of the growth as seen by a deterministic moving observer has the form |V-C|*D, where V and C is the speed of the observer and the second class particle, respectively, and D is a constant connected to the equilibrium distribution of the model. Our main result is a generalization of Ferrari and Fontes' result for simple exclusion process. Law of large numbers and central limit theorem are also proven. We need some properties of the motion of the second class particle, which are known for simple exclusion and are partly known for zero range processes, and which are proven here for! a type of deposition models and also for a t...
Phase Characterization of Cucumber Growth: A Chemical Gel Model
Directory of Open Access Journals (Sweden)
Bo Li
2016-01-01
Full Text Available Cucumber grows with complex phenomena by changing its volume and shape, which is not fully investigated and challenges agriculture and food safety industry. In order to understand the mechanism and to characterize the growth process, the cucumber is modeled as a hydrogel in swelling and its development is studied in both preharvest and postharvest stages. Based on thermodynamics, constitutive equations, incorporating biological quantities, are established. The growth behavior of cucumber follows the classic theory of continuous or discontinuous phase transition. The mechanism of bulged tail in cucumber is interpreted by phase coexistence and characterized by critical conditions. Conclusions are given for advances in food engineering and novel fabrication techniques in mechanical biology.
Dynamic density functional theory of solid tumor growth: Preliminary models
Directory of Open Access Journals (Sweden)
Arnaud Chauviere
2012-03-01
Full Text Available Cancer is a disease that can be seen as a complex system whose dynamics and growth result from nonlinear processes coupled across wide ranges of spatio-temporal scales. The current mathematical modeling literature addresses issues at various scales but the development of theoretical methodologies capable of bridging gaps across scales needs further study. We present a new theoretical framework based on Dynamic Density Functional Theory (DDFT extended, for the first time, to the dynamics of living tissues by accounting for cell density correlations, different cell types, phenotypes and cell birth/death processes, in order to provide a biophysically consistent description of processes across the scales. We present an application of this approach to tumor growth.
A new model for fungal hyphae growth using the thin viscous sheet equations
de Jong, T.G.; Prokert, G.; Hulshof, J.; Itou, H.; Kimura, M.; Chalupecký, V.; Ohtsuka, K.; Tagami, D.; Takada, A.
2016-01-01
In this paper, we model the growth of single nonbranching fungal hypha cell. The growth proceeds as an elongating expansion in a single direction. Modelling of hyphae growth consists out of two parts: transport of cell wall building material to the cell wall and growth of the cell wall as new cell
Stochastic resonance in a generalized Von Foerster population growth model
Energy Technology Data Exchange (ETDEWEB)
Lumi, N.; Mankin, R. [Institute of Mathematics and Natural Sciences, Tallinn University, 25 Narva Road, 10120 Tallinn (Estonia)
2014-11-12
The stochastic dynamics of a population growth model, similar to the Von Foerster model for human population, is studied. The influence of fluctuating environment on the carrying capacity is modeled as a multiplicative dichotomous noise. It is established that an interplay between nonlinearity and environmental fluctuations can cause single unidirectional discontinuous transitions of the mean population size versus the noise amplitude, i.e., an increase of noise amplitude can induce a jump from a state with a moderate number of individuals to that with a very large number, while by decreasing the noise amplitude an opposite transition cannot be effected. An analytical expression of the mean escape time for such transitions is found. Particularly, it is shown that the mean transition time exhibits a strong minimum at intermediate values of noise correlation time, i.e., the phenomenon of stochastic resonance occurs. Applications of the results in ecology are also discussed.
Ma, Q.; Su, Y.; Tao, S.; Guo, Q.
2016-12-01
Trees in the Sierra Nevada (SN) forests are experiencing rapid changes due to human disturbances and climatic changes. An improved monitoring of tree growth and understanding of how tree growth responses to different impact factors, such as tree competition, forest density, topographic and hydrologic conditions, are urgently needed in tree growth modeling. Traditional tree growth modeling mainly relied on field survey, which was highly time-consuming and labor-intensive. Airborne Light detection and ranging System (ALS) is increasingly used in forest survey, due to its high efficiency and accuracy in three-dimensional tree structure delineation and terrain characterization. This study successfully detected individual tree growth in height (ΔH), crown area (ΔA), and crown volume (ΔV) over a five-year period (2007-2012) using bi-temporal ALS data in two conifer forest areas in SN. We further analyzed their responses to original tree size, competition indices, forest structure indices, and topographic environmental parameters at individual tree and forest stand scales. Our results indicated ΔH was strongly sensitive to topographic wetness index; whereas ΔA and ΔV were highly responsive to forest density and original tree sizes. These ALS based findings in ΔH were consistent with field measurements. Our study demonstrated the promising potential of using bi-temporal ALS data in forest growth measurements and analysis. A more comprehensive study over a longer temporal period and a wider range of forest stands would give better insights into tree growth in the SN, and provide useful guides for forest growth monitoring, modeling, and management.
Modelling the interaction between flooding events and economic growth
Grames, Johanna; Fürnkranz-Prskawetz, Alexia; Grass, Dieter; Viglione, Alberto; Blöschl, Günter
2016-04-01
Recently socio-hydrology models have been proposed to analyze the interplay of community risk-coping culture, flooding damage and economic growth. These models descriptively explain the feedbacks between socio-economic development and natural disasters such as floods. Complementary to these descriptive models, we develop a dynamic optimization model, where the inter-temporal decision of an economic agent interacts with the hydrological system. This interdisciplinary approach matches with the goals of Panta Rhei i.e. to understand feedbacks between hydrology and society. It enables new perspectives but also shows limitations of each discipline. Young scientists need mentors from various scientific backgrounds to learn their different research approaches and how to best combine them such that interdisciplinary scientific work is also accepted by different science communities. In our socio-hydrology model we apply a macro-economic decision framework to a long-term flood-scenario. We assume a standard macro-economic growth model where agents derive utility from consumption and output depends on physical capital that can be accumulated through investment. To this framework we add the occurrence of flooding events which will destroy part of the capital. We identify two specific periodic long term solutions and denote them rich and poor economies. Whereas rich economies can afford to invest in flood defense and therefore avoid flood damage and develop high living standards, poor economies prefer consumption instead of investing in flood defense capital and end up facing flood damages every time the water level rises. Nevertheless, they manage to sustain at least a low level of physical capital. We identify optimal investment strategies and compare simulations with more frequent and more intense high water level events.
DEFF Research Database (Denmark)
Martinez Rios, Veronica; Dalgaard, Paw
Extensive growth and growth boundary models were developed and validated for psychrotolerant pseudomonads growing in seafood, meat and vegetable products. The new models were developed by expanding anexisting cardinal parameter-type model for growth of pseudomonads in milk (Martinez-Rios et al......, when observed and predicted μmax -values were compared. Thus, on average μmax -values for seafood and meat products were overestimated by 14%. Additionally, the reference growth rate parameter μref25˚C was calibrated by fitting the model to 21 μmax -values in vegetable products. This resulted in a μref......25˚C -value of 0.54 1/h. The calibrated vegetable model wassuccessfully validated using 51 μmax -values for psychrotolerant pseudomonads in vegetables. Average bias and accuracy factor values of 1.24 and 1.38 were obtained, respectively. Lag time models were developed by using relative lag times from...
International Nuclear Information System (INIS)
Valor, A.; Caleyo, F.; Alfonso, L.; Rivas, D.; Hallen, J.M.
2007-01-01
In this work, a new stochastic model capable of simulating pitting corrosion is developed and validated. Pitting corrosion is modeled as the combination of two stochastic processes: pit initiation and pit growth. Pit generation is modeled as a nonhomogeneous Poisson process, in which induction time for pit initiation is simulated as the realization of a Weibull process. In this way, the exponential and Weibull distributions can be considered as the possible distributions for pit initiation time. Pit growth is simulated using a nonhomogeneous Markov process. Extreme value statistics is used to find the distribution of maximum pit depths resulting from the combination of the initiation and growth processes for multiple pits. The proposed model is validated using several published experiments on pitting corrosion. It is capable of reproducing the experimental observations with higher quality than the stochastic models available in the literature for pitting corrosion
Energy Technology Data Exchange (ETDEWEB)
Valor, A. [Facultad de Fisica, Universidad de La Habana, San Lazaro y L, Vedado, 10400 Havana (Cuba); Caleyo, F. [Departamento de Ingenieria, Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico DF 07738 (Mexico)]. E-mail: fcaleyo@gmail.com; Alfonso, L. [Departamento de Ingenieria, Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico DF 07738 (Mexico); Rivas, D. [Departamento de Ingenieria, Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico DF 07738 (Mexico); Hallen, J.M. [Departamento de Ingenieria, Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico DF 07738 (Mexico)
2007-02-15
In this work, a new stochastic model capable of simulating pitting corrosion is developed and validated. Pitting corrosion is modeled as the combination of two stochastic processes: pit initiation and pit growth. Pit generation is modeled as a nonhomogeneous Poisson process, in which induction time for pit initiation is simulated as the realization of a Weibull process. In this way, the exponential and Weibull distributions can be considered as the possible distributions for pit initiation time. Pit growth is simulated using a nonhomogeneous Markov process. Extreme value statistics is used to find the distribution of maximum pit depths resulting from the combination of the initiation and growth processes for multiple pits. The proposed model is validated using several published experiments on pitting corrosion. It is capable of reproducing the experimental observations with higher quality than the stochastic models available in the literature for pitting corrosion.
A DYNAMIC-SYSTEMS MODEL OF COGNITIVE AND LANGUAGE GROWTH
VANGEERT, P
In the first part of the article, a conceptual framework is sketched to define cognitive growth, including language growth, as a process of growth under limited resources. Important concepts are the process, level, and rate of growth; minimal structural growth level; carrying capacity and unutilized
Modeling biological tissue growth: discrete to continuum representations.
Hywood, Jack D; Hackett-Jones, Emily J; Landman, Kerry A
2013-09-01
There is much interest in building deterministic continuum models from discrete agent-based models governed by local stochastic rules where an agent represents a biological cell. In developmental biology, cells are able to move and undergo cell division on and within growing tissues. A growing tissue is itself made up of cells which undergo cell division, thereby providing a significant transport mechanism for other cells within it. We develop a discrete agent-based model where domain agents represent tissue cells. Each agent has the ability to undergo a proliferation event whereby an additional domain agent is incorporated into the lattice. If a probability distribution describes the waiting times between proliferation events for an individual agent, then the total length of the domain is a random variable. The average behavior of these stochastically proliferating agents defining the growing lattice is determined in terms of a Fokker-Planck equation, with an advection and diffusion term. The diffusion term differs from the one obtained Landman and Binder [J. Theor. Biol. 259, 541 (2009)] when the rate of growth of the domain is specified, but the choice of agents is random. This discrepancy is reconciled by determining a discrete-time master equation for this process and an associated asymmetric nonexclusion random walk, together with consideration of synchronous and asynchronous updating schemes. All theoretical results are confirmed with numerical simulations. This study furthers our understanding of the relationship between agent-based rules, their implementation, and their associated partial differential equations. Since tissue growth is a significant cellular transport mechanism during embryonic growth, it is important to use the correct partial differential equation description when combining with other cellular functions.
BUILDING NEW BUSINESS MODELS FOR SUSTAINABLE GROWTH AND DEVELOPMENT
Directory of Open Access Journals (Sweden)
Taco C. R. van Someren
2011-06-01
Full Text Available Considered are issues of methodology and methods, as well as ideology of strategic innovation. Using the tools of this approach is offered as mechanisms to develop and build business models for sustainable socio-economic economic growth and development of different regions. The connection between key problems of sustainable development and management policy of different economic entities is studied. The consultancy company Ynnovate’s experience in addressing these issues in the EU and China is shown. It is offered to the use its experience and tools in exploring the areas of cross-border economic cooperation between territories of the Russian Far East and China
A mean-field game economic growth model
Gomes, Diogo A.
2016-08-05
Here, we examine a mean-field game (MFG) that models the economic growth of a population of non-cooperative, rational agents. In this MFG, agents are described by two state variables - the capital and consumer goods they own. Each agent seeks to maximize his/her utility by taking into account statistical data about the whole population. The individual actions drive the evolution of the players, and a market-clearing condition determines the relative price of capital and consumer goods. We study the existence and uniqueness of optimal strategies of the agents and develop numerical methods to compute these strategies and the equilibrium price.
A network growth model based on the evolutionary ultimatum game
International Nuclear Information System (INIS)
Deng, L L; Zhou, G G; Cai, J H; Wang, C; Tang, W S
2012-01-01
In this paper, we provide a network growth model with incorporation into the ultimatum game dynamics. The network grows on the basis of the payoff-oriented preferential attachment mechanism, where a new node is added into the network and attached preferentially to nodes with higher payoffs. The interplay between the network growth and the game dynamics gives rise to quite interesting dynamical behaviors. Simulation results show the emergence of altruistic behaviors in the ultimatum game, which is affected by the growing network structure. Compared with the static counterpart case, the levels of altruistic behaviors are promoted. The corresponding strategy distributions and wealth distributions are also presented to further demonstrate the strategy evolutionary dynamics. Subsequently, we turn to the topological properties of the evolved network, by virtue of some statistics. The most studied characteristic path length and the clustering coefficient of the network are shown to indicate their small-world effect. Then the degree distributions are analyzed to clarify the interplay of structure and evolutionary dynamics. In particular, the difference between our growth network and the static counterpart is revealed. To explain clearly the evolved networks, the rich-club ordering and the assortative mixing coefficient are exploited to reveal the degree correlation. (paper)
Modeling dust growth in protoplanetary disks: The breakthrough case
Drążkowska, J.; Windmark, F.; Dullemond, C. P.
2014-07-01
Context. Dust coagulation in protoplanetary disks is one of the initial steps toward planet formation. Simple toy models are often not sufficient to cover the complexity of the coagulation process, and a number of numerical approaches are therefore used, among which integration of the Smoluchowski equation and various versions of the Monte Carlo algorithm are the most popular. Aims: Recent progress in understanding the processes involved in dust coagulation have caused a need for benchmarking and comparison of various physical aspects of the coagulation process. In this paper, we directly compare the Smoluchowski and Monte Carlo approaches to show their advantages and disadvantages. Methods: We focus on the mechanism of planetesimal formation via sweep-up growth, which is a new and important aspect of the current planet formation theory. We use realistic test cases that implement a distribution in dust collision velocities. This allows a single collision between two grains to have a wide range of possible outcomes but also requires a very high numerical accuracy. Results: For most coagulation problems, we find a general agreement between the two approaches. However, for the sweep-up growth driven by the "lucky" breakthrough mechanism, the methods exhibit very different resolution dependencies. With too few mass bins, the Smoluchowski algorithm tends to overestimate the growth rate and the probability of breakthrough. The Monte Carlo method is less dependent on the number of particles in the growth timescale aspect but tends to underestimate the breakthrough chance due to its limited dynamic mass range. Conclusions: We find that the Smoluchowski approach, which is generally better for the breakthrough studies, is sensitive to low mass resolutions in the high-mass, low-number tail that is important in this scenario. To study the low number density features, a new modulation function has to be introduced to the interaction probabilities. As the minimum resolution
Determining of migraine prognosis using latent growth mixture models.
Tasdelen, Bahar; Ozge, Aynur; Kaleagasi, Hakan; Erdogan, Semra; Mengi, Tufan
2011-04-01
This paper presents a retrospective study to classify patients into subtypes of the treatment according to baseline and longitudinally observed values considering heterogenity in migraine prognosis. In the classical prospective clinical studies, participants are classified with respect to baseline status and followed within a certain time period. However, latent growth mixture model is the most suitable method, which considers the population heterogenity and is not affected drop-outs if they are missing at random. Hence, we planned this comprehensive study to identify prognostic factors in migraine. The study data have been based on a 10-year computer-based follow-up data of Mersin University Headache Outpatient Department. The developmental trajectories within subgroups were described for the severity, frequency, and duration of headache separately and the probabilities of each subgroup were estimated by using latent growth mixture models. SAS PROC TRAJ procedures, semiparametric and group-based mixture modeling approach, were applied to define the developmental trajectories. While the three-group model for the severity (mild, moderate, severe) and frequency (low, medium, high) of headache appeared to be appropriate, the four-group model for the duration (low, medium, high, extremely high) was more suitable. The severity of headache increased in the patients with nausea, vomiting, photophobia and phonophobia. The frequency of headache was especially related with increasing age and unilateral pain. Nausea and photophobia were also related with headache duration. Nausea, vomiting and photophobia were the most significant factors to identify developmental trajectories. The remission time was not the same for the severity, frequency, and duration of headache.
A Proposed Model for Protein Crystal Nucleation and Growth
Pusey, Marc; Curreri, Peter A. (Technical Monitor)
2002-01-01
How does one take a molecule, strongly asymmetric in both shape and charge distribution, and assemble it into a crystal? We propose a model for the nucleation and crystal growth process for tetragonal lysozyme, based upon fluorescence, light, neutron, and X-ray scattering data, size exclusion chromatography experiments, dialysis kinetics, AFM, and modeling of growth rate data, from this and other laboratories. The first species formed is postulated to be a 'head to side' dimer. Through repeating associations involving the same intermolecular interactions this grows to a 4(sub 3) helix structure, that in turn serves as the basic unit for nucleation and subsequent crystal growth. High salt attenuates surface charges while promoting hydrophobic interactions. Symmetry facilitates subsequent helix-helix self-association. Assembly stability is enhanced when a four helix structure is obtained, with each bound to two neighbors. Only two unique interactions are required. The first are those for helix formation, where the dominant interaction is the intermolecular bridging anion. The second is the anti-parallel side-by-side helix-helix interaction, guided by alternating pairs of symmetry related salt bridges along each side. At this stage all eight unique positions of the P4(sub3)2(sub 1),2(sub 1) unit cell are filled. The process is one of a) attenuating the most strongly interacting groups, such that b) the molecules begin to self-associate in defined patterns, so that c) symmetry is obtained, which d) propagates as a growing crystal. Simple and conceptually obvious in hindsight, this tells much about what we are empirically doing when we crystallize macromolecules. By adjusting the growth parameters we are empirically balancing the intermolecular interactions, preferentially attenuating the dominant strong (for lysozyme the charged groups) while strengthening the lesser strong (hydrophobic) interactions. In the general case for proteins the lack of a singularly defined
The Biasing Effects of Unmodeled ARMA Time Series Processes on Latent Growth Curve Model Estimates
Sivo, Stephen; Fan, Xitao; Witta, Lea
2005-01-01
The purpose of this study was to evaluate the robustness of estimated growth curve models when there is stationary autocorrelation among manifest variable errors. The results suggest that when, in practice, growth curve models are fitted to longitudinal data, alternative rival hypotheses to consider would include growth models that also specify…
A theoretical model of semi-elliptic surface crack growth
Directory of Open Access Journals (Sweden)
Shi Kaikai
2014-06-01
Full Text Available A theoretical model of semi-elliptic surface crack growth based on the low cycle strain damage accumulation near the crack tip along the cracking direction and the Newman–Raju formula is developed. The crack is regarded as a sharp notch with a small curvature radius and the process zone is assumed to be the size of cyclic plastic zone. The modified Hutchinson, Rice and Rosengren (HRR formulations are used in the presented study. Assuming that the shape of surface crack front is controlled by two critical points: the deepest point and the surface point. The theoretical model is applied to semi-elliptic surface cracked Al 7075-T6 alloy plate under cyclic loading, and five different initial crack shapes are discussed in present study. Good agreement between experimental and theoretical results is obtained.
Goodwyn, Andrew
2017-01-01
The Personal Growth (PG) model, as outlined by John Dixon in 1967, is unquestionably still recognisable to English teachers, remaining aligned to their philosophy of teaching English. This article traces a key aspect of the history of Personal Growth and explores present continuities traceable to Dartmouth in 1966, in suggesting an invigorated…
Grajeda, Laura M; Ivanescu, Andrada; Saito, Mayuko; Crainiceanu, Ciprian; Jaganath, Devan; Gilman, Robert H; Crabtree, Jean E; Kelleher, Dermott; Cabrera, Lilia; Cama, Vitaliano; Checkley, William
2016-01-01
Childhood growth is a cornerstone of pediatric research. Statistical models need to consider individual trajectories to adequately describe growth outcomes. Specifically, well-defined longitudinal models are essential to characterize both population and subject-specific growth. Linear mixed-effect models with cubic regression splines can account for the nonlinearity of growth curves and provide reasonable estimators of population and subject-specific growth, velocity and acceleration. We provide a stepwise approach that builds from simple to complex models, and account for the intrinsic complexity of the data. We start with standard cubic splines regression models and build up to a model that includes subject-specific random intercepts and slopes and residual autocorrelation. We then compared cubic regression splines vis-à-vis linear piecewise splines, and with varying number of knots and positions. Statistical code is provided to ensure reproducibility and improve dissemination of methods. Models are applied to longitudinal height measurements in a cohort of 215 Peruvian children followed from birth until their fourth year of life. Unexplained variability, as measured by the variance of the regression model, was reduced from 7.34 when using ordinary least squares to 0.81 (p linear mixed-effect models with random slopes and a first order continuous autoregressive error term. There was substantial heterogeneity in both the intercept (p modeled with a first order continuous autoregressive error term as evidenced by the variogram of the residuals and by a lack of association among residuals. The final model provides a parametric linear regression equation for both estimation and prediction of population- and individual-level growth in height. We show that cubic regression splines are superior to linear regression splines for the case of a small number of knots in both estimation and prediction with the full linear mixed effect model (AIC 19,352 vs. 19
Modelling the interaction between flooding events and economic growth
Grames, Johanna; Grass, Dieter; Prskawetz, Alexia; Blöschl, Günther
2015-04-01
Socio-hydrology describes the interaction between the socio-economy, water and population dynamics. Recent models analyze the interplay of community risk-coping culture, flooding damage and economic growth (Di Baldassarre, 2013, Viglione, 2014). These models descriptively explain the feedbacks between socio-economic development and natural disasters like floods. Contrary to these descriptive models, our approach develops an optimization model, where the intertemporal decision of an economic agent interacts with the hydrological system. This is the first economic growth model describing the interaction between the consumption and investment decisions of an economic agent and the occurrence of flooding events: Investments in defense capital can avoid floods even when the water level is high, but on the other hand such investment competes with investment in productive capital and hence may reduce the level of consumption. When floods occur, the flood damage therefore depends on the existing defense capital. The aim is to find an optimal tradeoff between investments in productive versus defense capital such as to optimize the stream of consumption in the long-term. We assume a non-autonomous exogenous periodic rainfall function (Yevjevich et.al. 1990, Zakaria 2001) which implies that the long-term equilibrium will be periodic . With our model we aim to derive mechanisms that allow consumption smoothing in the long term, and at the same time allow for optimal investment in flood defense to maximize economic output. We choose an aggregate welfare function that depends on the consumption level of the society as the objective function. I.e. we assume a social planer with perfect foresight that maximizes the aggregate welfare function. Within our model framework we can also study whether the path and level of defense capital (that protects people from floods) is related to the time preference rate of the social planner. Our model also allows to investigate how the frequency
Matrix models and stochastic growth in Donaldson-Thomas theory
Energy Technology Data Exchange (ETDEWEB)
Szabo, Richard J. [Department of Mathematics, Heriot-Watt University, Colin Maclaurin Building, Riccarton, Edinburgh EH14 4AS, United Kingdom and Maxwell Institute for Mathematical Sciences, Edinburgh (United Kingdom); Tierz, Miguel [Grupo de Fisica Matematica, Complexo Interdisciplinar da Universidade de Lisboa, Av. Prof. Gama Pinto, 2, PT-1649-003 Lisboa (Portugal); Departamento de Analisis Matematico, Facultad de Ciencias Matematicas, Universidad Complutense de Madrid, Plaza de Ciencias 3, 28040 Madrid (Spain)
2012-10-15
We show that the partition functions which enumerate Donaldson-Thomas invariants of local toric Calabi-Yau threefolds without compact divisors can be expressed in terms of specializations of the Schur measure. We also discuss the relevance of the Hall-Littlewood and Jack measures in the context of BPS state counting and study the partition functions at arbitrary points of the Kaehler moduli space. This rewriting in terms of symmetric functions leads to a unitary one-matrix model representation for Donaldson-Thomas theory. We describe explicitly how this result is related to the unitary matrix model description of Chern-Simons gauge theory. This representation is used to show that the generating functions for Donaldson-Thomas invariants are related to tau-functions of the integrable Toda and Toeplitz lattice hierarchies. The matrix model also leads to an interpretation of Donaldson-Thomas theory in terms of non-intersecting paths in the lock-step model of vicious walkers. We further show that these generating functions can be interpreted as normalization constants of a corner growth/last-passage stochastic model.
Matrix models and stochastic growth in Donaldson-Thomas theory
International Nuclear Information System (INIS)
Szabo, Richard J.; Tierz, Miguel
2012-01-01
We show that the partition functions which enumerate Donaldson-Thomas invariants of local toric Calabi-Yau threefolds without compact divisors can be expressed in terms of specializations of the Schur measure. We also discuss the relevance of the Hall-Littlewood and Jack measures in the context of BPS state counting and study the partition functions at arbitrary points of the Kähler moduli space. This rewriting in terms of symmetric functions leads to a unitary one-matrix model representation for Donaldson-Thomas theory. We describe explicitly how this result is related to the unitary matrix model description of Chern-Simons gauge theory. This representation is used to show that the generating functions for Donaldson-Thomas invariants are related to tau-functions of the integrable Toda and Toeplitz lattice hierarchies. The matrix model also leads to an interpretation of Donaldson-Thomas theory in terms of non-intersecting paths in the lock-step model of vicious walkers. We further show that these generating functions can be interpreted as normalization constants of a corner growth/last-passage stochastic model.
Short-ranged memory model with preferential growth
Schaigorodsky, Ana L.; Perotti, Juan I.; Almeira, Nahuel; Billoni, Orlando V.
2018-02-01
In this work we introduce a variant of the Yule-Simon model for preferential growth by incorporating a finite kernel to model the effects of bounded memory. We characterize the properties of the model combining analytical arguments with extensive numerical simulations. In particular, we analyze the lifetime and popularity distributions by mapping the model dynamics to corresponding Markov chains and branching processes, respectively. These distributions follow power laws with well-defined exponents that are within the range of the empirical data reported in ecologies. Interestingly, by varying the innovation rate, this simple out-of-equilibrium model exhibits many of the characteristics of a continuous phase transition and, around the critical point, it generates time series with power-law popularity, lifetime and interevent time distributions, and nontrivial temporal correlations, such as a bursty dynamics in analogy with the activity of solar flares. Our results suggest that an appropriate balance between innovation and oblivion rates could provide an explanatory framework for many of the properties commonly observed in many complex systems.
Bridging process-based and empirical approaches to modeling tree growth
Harry T. Valentine; Annikki Makela; Annikki Makela
2005-01-01
The gulf between process-based and empirical approaches to modeling tree growth may be bridged, in part, by the use of a common model. To this end, we have formulated a process-based model of tree growth that can be fitted and applied in an empirical mode. The growth model is grounded in pipe model theory and an optimal control model of crown development. Together, the...
Formation of algae growth constitutive relations for improved algae modeling.
Energy Technology Data Exchange (ETDEWEB)
Gharagozloo, Patricia E.; Drewry, Jessica Louise.
2013-01-01
This SAND report summarizes research conducted as a part of a two year Laboratory Directed Research and Development (LDRD) project to improve our abilities to model algal cultivation. Algae-based biofuels have generated much excitement due to their potentially large oil yield from relatively small land use and without interfering with the food or water supply. Algae mitigate atmospheric CO2 through metabolism. Efficient production of algal biofuels could reduce dependence on foreign oil by providing a domestic renewable energy source. Important factors controlling algal productivity include temperature, nutrient concentrations, salinity, pH, and the light-to-biomass conversion rate. Computational models allow for inexpensive predictions of algae growth kinetics in these non-ideal conditions for various bioreactor sizes and geometries without the need for multiple expensive measurement setups. However, these models need to be calibrated for each algal strain. In this work, we conduct a parametric study of key marine algae strains and apply the findings to a computational model.
Modelling of tomato stem diameter growth rate based on physiological responses
International Nuclear Information System (INIS)
Li, L.; Tan, J.; Lv, T.
2017-01-01
The stem diameter is an important parameter describing the growth of tomato plant during vegetative growth stage. A stem diameter growth model was developed to predict the response of plant growth under different conditions. By analyzing the diurnal variations of stem diameter in tomato (Solanum lycopersicum L.), it was found that the stem diameter measured at 3:00 am was the representative value as the daily basis of tomato stem diameter. Based on the responses of growth rate in stem diameter to light and temperature, a linear regression relationship was applied to establish the stem diameter growth rate prediction model for the vegetative growth stage in tomato and which was further validated by experiment. The root mean square error (RMSE) and relative error (RE) were used to test the correlation between measured and modeled stem diameter variations. Results showed that the model can be used in prediction for stem diameter growth rate at vegetative growth stage in tomato. (author)
Visualization modeling of thin film growth in photodeposition processes
International Nuclear Information System (INIS)
Mirchin, N.; Sidi, M.; Muchnik, Y.; Peled, A.
2003-01-01
A computer visualization technique, which analyzes and predicts the spatio-temporal evolution of thin film deposition and growth processes is given. It relies on microscopy sampled or computer generated synthetic micrographs of particles. These are then simulated for deposition, aggregation and coagulation during thin film growth by frequency domain transform techniques. Particle sources and diffusion operators on surfaces are used to predict with high temporal resolution, unattained by real world microscopy the surface structure evolution as time samples and time movies. The simulation program was used to investigate deposition and diffusive profiles in photodeposition experiments, starting from initial synthetic micrographs based on real world scanning electron microscopy (SEM) images. The surface microstructure time 'tracking' scheme described here relies on transforming the original image of the deposited particles into a Fourier spatial frequency domain image. The physical models used are that of a material random deposition source and subsequent surface redistribution due to diffusion and other coalescence material surface flow mechanisms. The 2-D inverse Fourier transform (IFT) is finally used to obtain back the real space-time images representing the surface spatio-temporal films morphology changes. False color representation of the images allows for a better discrimination of the films growing details especially during the fast pre-compact thin film layer formation on the substrate
Visualization modeling of thin film growth in photodeposition processes
Energy Technology Data Exchange (ETDEWEB)
Mirchin, N.; Sidi, M.; Muchnik, Y.; Peled, A
2003-03-15
A computer visualization technique, which analyzes and predicts the spatio-temporal evolution of thin film deposition and growth processes is given. It relies on microscopy sampled or computer generated synthetic micrographs of particles. These are then simulated for deposition, aggregation and coagulation during thin film growth by frequency domain transform techniques. Particle sources and diffusion operators on surfaces are used to predict with high temporal resolution, unattained by real world microscopy the surface structure evolution as time samples and time movies. The simulation program was used to investigate deposition and diffusive profiles in photodeposition experiments, starting from initial synthetic micrographs based on real world scanning electron microscopy (SEM) images. The surface microstructure time 'tracking' scheme described here relies on transforming the original image of the deposited particles into a Fourier spatial frequency domain image. The physical models used are that of a material random deposition source and subsequent surface redistribution due to diffusion and other coalescence material surface flow mechanisms. The 2-D inverse Fourier transform (IFT) is finally used to obtain back the real space-time images representing the surface spatio-temporal films morphology changes. False color representation of the images allows for a better discrimination of the films growing details especially during the fast pre-compact thin film layer formation on the substrate.
Investigation of Mediational Processes Using Parallel Process Latent Growth Curve Modeling
Cheong, JeeWon; MacKinnon, David P.; Khoo, Siek Toon
2010-01-01
This study investigated a method to evaluate mediational processes using latent growth curve modeling. The mediator and the outcome measured across multiple time points were viewed as 2 separate parallel processes. The mediational process was defined as the independent variable influencing the growth of the mediator, which, in turn, affected the growth of the outcome. To illustrate modeling procedures, empirical data from a longitudinal drug prevention program, Adolescents Training and Learning to Avoid Steroids, were used. The program effects on the growth of the mediator and the growth of the outcome were examined first in a 2-group structural equation model. The mediational process was then modeled and tested in a parallel process latent growth curve model by relating the prevention program condition, the growth rate factor of the mediator, and the growth rate factor of the outcome. PMID:20157639
Software reliability growth model for safety systems of nuclear reactor
International Nuclear Information System (INIS)
Thirugnana Murthy, D.; Murali, N.; Sridevi, T.; Satya Murty, S.A.V.; Velusamy, K.
2014-01-01
The demand for complex software systems has increased more rapidly than the ability to design, implement, test, and maintain them, and the reliability of software systems has become a major concern for our, modern society.Software failures have impaired several high visibility programs in space, telecommunications, defense and health industries. Besides the costs involved, it setback the projects. The ways of quantifying it and using it for improvement and control of the software development and maintenance process. This paper discusses need for systematic approaches for measuring and assuring software reliability which is a major share of project development resources. It covers the reliability models with the concern on 'Reliability Growth'. It includes data collection on reliability, statistical estimation and prediction, metrics and attributes of product architecture, design, software development, and the operational environment. Besides its use for operational decisions like deployment, it includes guiding software architecture, development, testing and verification and validation. (author)
Growth and Division in a Dynamic Protocell Model
Directory of Open Access Journals (Sweden)
Marco Villani
2014-12-01
Full Text Available In this paper a new model of growing and dividing protocells is described, whose main features are (i a lipid container that grows according to the composition of the molecular milieu (ii a set of “genetic memory molecules” (GMMs that undergo catalytic reactions in the internal aqueous phase and (iii a set of stochastic kinetic equations for the GMMs. The mass exchange between the external environment and the internal phase is described by simulating a semipermeable membrane and a flow driven by the differences in chemical potentials, thereby avoiding to resort to sometimes misleading simplifications, e.g., that of a flow reactor. Under simple assumptions, it is shown that synchronization takes place between the rate of replication of the GMMs and that of the container, provided that the set of reactions hosts a so-called RAF (Reflexive Autocatalytic, Food-generated set whose influence on synchronization is hereafter discussed. It is also shown that a slight modification of the basic model that takes into account a rate-limiting term, makes possible the growth of novelties, allowing in such a way suitable evolution: so the model represents an effective basis for understanding the main abstract properties of populations of protocells.
Overview: early history of crop growth and photosynthesis modeling.
El-Sharkawy, Mabrouk A
2011-02-01
As in industrial and engineering systems, there is a need to quantitatively study and analyze the many constituents of complex natural biological systems as well as agro-ecosystems via research-based mechanistic modeling. This objective is normally addressed by developing mathematically built descriptions of multilevel biological processes to provide biologists a means to integrate quantitatively experimental research findings that might lead to a better understanding of the whole systems and their interactions with surrounding environments. Aided with the power of computational capacities associated with computer technology then available, pioneering cropping systems simulations took place in the second half of the 20th century by several research groups across continents. This overview summarizes that initial pioneering effort made to simulate plant growth and photosynthesis of crop canopies, focusing on the discovery of gaps that exist in the current scientific knowledge. Examples are given for those gaps where experimental research was needed to improve the validity and application of the constructed models, so that their benefit to mankind was enhanced. Such research necessitates close collaboration among experimentalists and model builders while adopting a multidisciplinary/inter-institutional approach. Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.
Modeling pitting growth data and predicting degradation trend
International Nuclear Information System (INIS)
Viglasky, T.; Awad, R.; Zeng, Z.; Riznic, J.
2007-01-01
A non-statistical modeling approach to predict material degradation is presented in this paper. In this approach, the original data series is processed using Accumulated Generating Operation (AGO). With the aid of the AGO which weakens the random fluctuation embedded in the data series, an approximately exponential curve is established. The generated data series described by the exponential curve is then modeled by a differential equation. The coefficients of the differential equation can be deduced by approximate difference formula based on least-squares algorithm. By solving the differential equation and processing an inverse AGO, a predictive model can be obtained. As this approach is not established on the basis of statistics, the prediction can be performed with a limited amount of data. Implementation of this approach is demonstrated by predicting the pitting growth rate in specimens and wear trend in steam generator tubes. The analysis results indicate that this approach provides a powerful tool with reasonable precision to predict material degradation. (author)
Mathematical modelling of the growth of human fetus anatomical structures.
Dudek, Krzysztof; Kędzia, Wojciech; Kędzia, Emilia; Kędzia, Alicja; Derkowski, Wojciech
2017-09-01
The goal of this study was to present a procedure that would enable mathematical analysis of the increase of linear sizes of human anatomical structures, estimate mathematical model parameters and evaluate their adequacy. Section material consisted of 67 foetuses-rectus abdominis muscle and 75 foetuses- biceps femoris muscle. The following methods were incorporated to the study: preparation and anthropologic methods, image digital acquisition, Image J computer system measurements and statistical analysis method. We used an anthropologic method based on age determination with the use of crown-rump length-CRL (V-TUB) by Scammon and Calkins. The choice of mathematical function should be based on a real course of the curve presenting growth of anatomical structure linear size Ύ in subsequent weeks t of pregnancy. Size changes can be described with a segmental-linear model or one-function model with accuracy adequate enough for clinical purposes. The interdependence of size-age is described with many functions. However, the following functions are most often considered: linear, polynomial, spline, logarithmic, power, exponential, power-exponential, log-logistic I and II, Gompertz's I and II and von Bertalanffy's function. With the use of the procedures described above, mathematical models parameters were assessed for V-PL (the total length of body) and CRL body length increases, rectus abdominis total length h, its segments hI, hII, hIII, hIV, as well as biceps femoris length and width of long head (LHL and LHW) and of short head (SHL and SHW). The best adjustments to measurement results were observed in the exponential and Gompertz's models.
Growth models for morphological traits of sunn hemp
Directory of Open Access Journals (Sweden)
Cláudia Marques de Bem
2017-10-01
Full Text Available The objective of the present study was to fit Gompertz and Logistic nonlinear to descriptions of morphological traits of sunn hemp. Two uniformity trials were conducted and the crops received identical treatment in all experimental area. Sunn hemp seeds were sown in rows 0.5 m apart with a plant density of 20 plants per row meter in a usable area of 52 m × 50 m. The following morphological traits were evaluated: plant height (PH, number of leaves (NL, stem diameter (SD, and root length (RL. These traits were assessed daily during two sowing periods—seeds were sown on October 22, 2014 (first period and December 3, 2014 (second period. Four plants were randomly collected daily, beginning 7 days after first period and 13 days after for second period, totaling 94 and 76 evaluation days, respectively. For Gompertz models the equation was used y=a*e^((?-e?^((b-c*xiand Logistic models the equation was used yi= a/(1+e^((-b-c*xi. The inflection points of the Gompertz and Logistic models were calculated and the goodness of fit was quantified using the adjusted coefficient of determination, Akaike information criterion, standard deviation of residuals, mean absolute deviation, mean absolute percentage error, and mean prediction error. Differences were observed between the Gompertz and Logistic models and between the experimental periods in the parameter estimate for all morphological traits measured. Satisfactory growth curve fittings were achieved for plant height, number of leaves, and stem diameter in both models using the evaluation criteria: coefficient of determination (R², Akaike information criterion (AIC, standard deviation of residuals (SDR, mean absolute deviation (MAD, mean absolute percentage error (MAPE, and mean prediction error (MPE.
A Finite Element Model for Mixed Porohyperelasticity with Transport, Swelling, and Growth.
Directory of Open Access Journals (Sweden)
Michelle Hine Armstrong
Full Text Available The purpose of this manuscript is to establish a unified theory of porohyperelasticity with transport and growth and to demonstrate the capability of this theory using a finite element model developed in MATLAB. We combine the theories of volumetric growth and mixed porohyperelasticity with transport and swelling (MPHETS to derive a new method that models growth of biological soft tissues. The conservation equations and constitutive equations are developed for both solid-only growth and solid/fluid growth. An axisymmetric finite element framework is introduced for the new theory of growing MPHETS (GMPHETS. To illustrate the capabilities of this model, several example finite element test problems are considered using model geometry and material parameters based on experimental data from a porcine coronary artery. Multiple growth laws are considered, including time-driven, concentration-driven, and stress-driven growth. Time-driven growth is compared against an exact analytical solution to validate the model. For concentration-dependent growth, changing the diffusivity (representing a change in drug fundamentally changes growth behavior. We further demonstrate that for stress-dependent, solid-only growth of an artery, growth of an MPHETS model results in a more uniform hoop stress than growth in a hyperelastic model for the same amount of growth time using the same growth law. This may have implications in the context of developing residual stresses in soft tissues under intraluminal pressure. To our knowledge, this manuscript provides the first full description of an MPHETS model with growth. The developed computational framework can be used in concert with novel in-vitro and in-vivo experimental approaches to identify the governing growth laws for various soft tissues.
A Finite Element Model for Mixed Porohyperelasticity with Transport, Swelling, and Growth.
Armstrong, Michelle Hine; Buganza Tepole, Adrián; Kuhl, Ellen; Simon, Bruce R; Vande Geest, Jonathan P
2016-01-01
The purpose of this manuscript is to establish a unified theory of porohyperelasticity with transport and growth and to demonstrate the capability of this theory using a finite element model developed in MATLAB. We combine the theories of volumetric growth and mixed porohyperelasticity with transport and swelling (MPHETS) to derive a new method that models growth of biological soft tissues. The conservation equations and constitutive equations are developed for both solid-only growth and solid/fluid growth. An axisymmetric finite element framework is introduced for the new theory of growing MPHETS (GMPHETS). To illustrate the capabilities of this model, several example finite element test problems are considered using model geometry and material parameters based on experimental data from a porcine coronary artery. Multiple growth laws are considered, including time-driven, concentration-driven, and stress-driven growth. Time-driven growth is compared against an exact analytical solution to validate the model. For concentration-dependent growth, changing the diffusivity (representing a change in drug) fundamentally changes growth behavior. We further demonstrate that for stress-dependent, solid-only growth of an artery, growth of an MPHETS model results in a more uniform hoop stress than growth in a hyperelastic model for the same amount of growth time using the same growth law. This may have implications in the context of developing residual stresses in soft tissues under intraluminal pressure. To our knowledge, this manuscript provides the first full description of an MPHETS model with growth. The developed computational framework can be used in concert with novel in-vitro and in-vivo experimental approaches to identify the governing growth laws for various soft tissues.
Forest evaporation models: Relationships between stand growth and evaporation
CSIR Research Space (South Africa)
Le Maitre, David C
1997-06-01
Full Text Available The relationships between forest stand structure, growth and evaporation were analysed to determine whether forest evaporation can be estimated from stand growth data. This approach permits rapid assessment of the potential impacts of afforestation...
Modelling and predicting growth of psychrotolerant pseudomonads in milk and cottage cheese
DEFF Research Database (Denmark)
Martinez Rios, Veronica; Østergaard, Nina Bjerre; Rosshaug, Per Sand
.43. The acceptable simulation zone method showed the new model for cottage cheese to successfully predict growth of psychrotolerant pseudomonads at both constant and dynamic temperature storage conditions. The new models can be used together with the Food Spoilage and Safety Predictor (FSSP) software to predict......Mathematical models were developed and evaluated for growth of psychrotolerant pseudomonads in chilled milk and cottage cheese with cultured cream dressing. The mathematical models include the effect of temperature, pH, NaCl, lactic acid and sorbic acid. A simplified cardinal parameter growth model...... was developed based on growth in broth. Subsequently, the reference growth rate parameter (μref at 25 °C) was fitted to a total of 35 growth rates from cottage cheese with cultured cream dressing. Growth rate models for milk and cottage cheese were evaluated by comparison with data from literature and new...
Generic global regression models for growth prediction of Salmonella in ground pork and pork cuts
DEFF Research Database (Denmark)
Buschhardt, Tasja; Hansen, Tina Beck; Bahl, Martin Iain
2017-01-01
Introduction and Objectives Models for the prediction of bacterial growth in fresh pork are primarily developed using two-step regression (i.e. primary models followed by secondary models). These models are also generally based on experiments in liquids or ground meat and neglect surface growth....... It has been shown that one-step global regressions can result in more accurate models and that bacterial growth on intact surfaces can substantially differ from growth in liquid culture. Material and Methods We used a global-regression approach to develop predictive models for the growth of Salmonella....... One part of obtained logtransformed cell counts was used for model development and another for model validation. The Ratkowsky square root model and the relative lag time (RLT) model were integrated into the logistic model with delay. Fitted parameter estimates were compared to investigate the effect...
Modeling growth performances, survival, and feed efficiency of four ...
African Journals Online (AJOL)
Evolution of growth rate with age was similar in the four groups, but significant differences of growth curve parameters were found among breeds and/or sexes. Estimated hatch weight was lower in C hens and higher in FT hens. Initial specific growth rates and asymptotic body weight were higher in males for all breeds.
Specification Search for Identifying the Correct Mean Trajectory in Polynomial Latent Growth Models
Kim, Minjung; Kwok, Oi-Man; Yoon, Myeongsun; Willson, Victor; Lai, Mark H. C.
2016-01-01
This study investigated the optimal strategy for model specification search under the latent growth modeling (LGM) framework, specifically on searching for the correct polynomial mean or average growth model when there is no a priori hypothesized model in the absence of theory. In this simulation study, the effectiveness of different starting…
Plant Growth Modeling Using L-System Approach and Its Visualization
Directory of Open Access Journals (Sweden)
Atris Suyantohadi
2011-05-01
Full Text Available The visualizationof plant growth modeling using computer simulation has rarely been conducted with Lindenmayer System (L-System approach. L-System generally has been used as framework for improving and designing realistic modeling on plant growth. It is one kind of tools for representing plant growth based on grammar sintax and mathematic formulation. This research aimed to design modeling and visualizing plant growth structure generated using L-System. The environment on modeling design used three dimension graphic on standart OpenGL format. The visualization on system design has been developed by some of L-System grammar, and the output graphic on three dimension reflected on plant growth as a virtual plant growth system. Using some of samples on grammar L-System rules for describing of the charaterictics of plant growth, the visualization of structure on plant growth has been resulted and demonstrated.
Depaoli, Sarah; van de Schoot, Rens; van Loey, Nancy; Sijbrandij, Marit
2015-01-01
BACKGROUND: After traumatic events, such as disaster, war trauma, and injuries including burns (which is the focus here), the risk to develop posttraumatic stress disorder (PTSD) is approximately 10% (Breslau & Davis, 1992). Latent Growth Mixture Modeling can be used to classify individuals into
Cluster Dynamics Modeling with Bubble Nucleation, Growth and Coalescence
Energy Technology Data Exchange (ETDEWEB)
de Almeida, Valmor F. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Blondel, Sophie [Univ. of Tennessee, Knoxville, TN (United States); Bernholdt, David E. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Wirth, Brian D. [Univ. of Tennessee, Knoxville, TN (United States)
2017-06-01
The topic of this communication pertains to defect formation in irradiated solids such as plasma-facing tungsten submitted to helium implantation in fusion reactor com- ponents, and nuclear fuel (metal and oxides) submitted to volatile ssion product generation in nuclear reactors. The purpose of this progress report is to describe ef- forts towards addressing the prediction of long-time evolution of defects via continuum cluster dynamics simulation. The di culties are twofold. First, realistic, long-time dynamics in reactor conditions leads to a non-dilute di usion regime which is not accommodated by the prevailing dilute, stressless cluster dynamics theory. Second, long-time dynamics calls for a large set of species (ideally an in nite set) to capture all possible emerging defects, and this represents a computational bottleneck. Extensions beyond the dilute limit is a signi cant undertaking since no model has been advanced to extend cluster dynamics to non-dilute, deformable conditions. Here our proposed approach to model the non-dilute limit is to monitor the appearance of a spatially localized void volume fraction in the solid matrix with a bell shape pro le and insert an explicit geometrical bubble onto the support of the bell function. The newly cre- ated internal moving boundary provides the means to account for the interfacial ux of mobile species into the bubble, and the growth of bubbles allows for coalescence phenomena which captures highly non-dilute interactions. We present a preliminary interfacial kinematic model with associated interfacial di usion transport to follow the evolution of the bubble in any number of spatial dimensions and any number of bubbles, which can be further extended to include a deformation theory. Finally we comment on a computational front-tracking method to be used in conjunction with conventional cluster dynamics simulations in the non-dilute model proposed.
NA
2005-01-01
This paper presents a study of errors in forecasting the population of Metropolitan Statistical Areas and the Primary MSAs of Consolidated Metropolitan Statistical Areas and New England MAs. The forecasts are for the year 2000 and are based on a semi-structural model estimated by Mills and Lubelle using 1970 to 1990 census data on population, employment and relative real wages. This model allows the testing of regional effects on population and employment growth. The year 2000 forecasts are f...
The FDI-growth hypothesis: A VAR model for Nigeria
Directory of Open Access Journals (Sweden)
PA Olomola
2004-07-01
Full Text Available The objective of this study was to examine the causal relationship between foreign direct investment and economic growth in Nigeria using annual data covering the period 1970 to 2002. The study employed the Granger causality procedure to test the direction of causality between foreign direct investment and economic growth for the Nigerian economy. The endogenous production function was derived to accommodate foreign investment and other domestic policies that could influence growth and foreign investment. The study found a one-way causality between from foreign direct investment to economic growth. The implication arising from this study is that Nigeria should adopt policy whereby FDI is attracted to promote economic growth.
MODELING THE RED SEQUENCE: HIERARCHICAL GROWTH YET SLOW LUMINOSITY EVOLUTION
International Nuclear Information System (INIS)
Skelton, Rosalind E.; Bell, Eric F.; Somerville, Rachel S.
2012-01-01
We explore the effects of mergers on the evolution of massive early-type galaxies by modeling the evolution of their stellar populations in a hierarchical context. We investigate how a realistic red sequence population set up by z ∼ 1 evolves under different assumptions for the merger and star formation histories, comparing changes in color, luminosity, and mass. The purely passive fading of existing red sequence galaxies, with no further mergers or star formation, results in dramatic changes at the bright end of the luminosity function and color-magnitude relation. Without mergers there is too much evolution in luminosity at a fixed space density compared to observations. The change in color and magnitude at a fixed mass resembles that of a passively evolving population that formed relatively recently, at z ∼ 2. Mergers among the red sequence population ('dry mergers') occurring after z = 1 build up mass, counteracting the fading of the existing stellar populations to give smaller changes in both color and luminosity for massive galaxies. By allowing some galaxies to migrate from the blue cloud onto the red sequence after z = 1 through gas-rich mergers, younger stellar populations are added to the red sequence. This manifestation of the progenitor bias increases the scatter in age and results in even smaller changes in color and luminosity between z = 1 and z = 0 at a fixed mass. The resultant evolution appears much slower, resembling the passive evolution of a population that formed at high redshift (z ∼ 3-5), and is in closer agreement with observations. We conclude that measurements of the luminosity and color evolution alone are not sufficient to distinguish between the purely passive evolution of an old population and cosmologically motivated hierarchical growth, although these scenarios have very different implications for the mass growth of early-type galaxies over the last half of cosmic history.
Modeling wormhole growth and wormhole networks in unconsolidated sand media using the BP CHOPS model
Energy Technology Data Exchange (ETDEWEB)
Vanderheyden, W.B. [BP America, Inc. Exploration and Production Technology Unconventional Oil Flagship (United States); Zhang, D. Z.; Jayaraman, B. [Los Alamos National Laboratory Theoretical Division Solid and Fluid Dynamics Group (United States)
2011-07-01
Cold Heavy Oil Production with Sand (CHOPS) is a recovery method used in unconsolidated sands to produce heavy oil. During the use of the CHOPS method, wormholes originating from production wells are generated. The aim of this paper is to present 2 modeling tools developed by BP in order to improve reservoir simulation of CHOPS operations with wormholes. The first tool developed is a CHOPS modeling framework representing wormhole networks through reservoir simulation and its wellbore model. The second one consists of the application of advanced fluid-structure interaction modeling into the simulation of wormhole and its network growth. Experiments were carried out and a qualitative agreement was achieved with the model. In addition the BP CHOPS model can predict probable oil production without calibration. This paper presented an improved model for reservoir simulation with wormholes but further work is required to predict wormhole shape in a more accurate manner.
International Nuclear Information System (INIS)
McAneney, H; O'Rourke, S F C
2007-01-01
The standard linear-quadratic survival model for radiotherapy is used to investigate different schedules of radiation treatment planning to study how these may be affected by different tumour repopulation kinetics between treatments. The laws for tumour cell repopulation include the logistic and Gompertz models and this extends the work of Wheldon et al (1977 Br. J. Radiol. 50 681), which was concerned with the case of exponential re-growth between treatments. Here we also consider the restricted exponential model. This has been successfully used by Panetta and Adam (1995 Math. Comput. Modelling 22 67) in the case of chemotherapy treatment planning.Treatment schedules investigated include standard fractionation of daily treatments, weekday treatments, accelerated fractionation, optimized uniform schedules and variation of the dosage and α/β ratio, where α and β are radiobiological parameters for the tumour tissue concerned. Parameters for these treatment strategies are extracted from the literature on advanced head and neck cancer, prostate cancer, as well as radiosensitive parameters. Standardized treatment protocols are also considered. Calculations based on the present analysis indicate that even with growth laws scaled to mimic initial growth, such that growth mechanisms are comparable, variation in survival fraction to orders of magnitude emerged. Calculations show that the logistic and exponential models yield similar results in tumour eradication. By comparison the Gompertz model calculations indicate that tumours described by this law result in a significantly poorer prognosis for tumour eradication than either the exponential or logistic models. The present study also shows that the faster the tumour growth rate and the higher the repair capacity of the cell line, the greater the variation in outcome of the survival fraction. Gaps in treatment, planned or unplanned, also accentuate the differences of the survival fraction given alternative growth
Troy, Tara J.; Ines, Amor V. M.; Lall, Upmanu; Robertson, Andrew W.
2013-04-01
Large-scale hydrologic models, such as the Variable Infiltration Capacity (VIC) model, are used for a variety of studies, from drought monitoring to projecting the potential impact of climate change on the hydrologic cycle decades in advance. The majority of these models simulates the natural hydrological cycle and neglects the effects of human activities such as irrigation, which can result in streamflow withdrawals and increased evapotranspiration. In some parts of the world, these activities do not significantly affect the hydrologic cycle, but this is not the case in south Asia where irrigated agriculture has a large water footprint. To address this gap, we incorporate a crop growth model and irrigation model into the VIC model in order to simulate the impacts of irrigated and rainfed agriculture on the hydrologic cycle over south Asia (Indus, Ganges, and Brahmaputra basin and peninsular India). The crop growth model responds to climate signals, including temperature and water stress, to simulate the growth of maize, wheat, rice, and millet. For the primarily rainfed maize crop, the crop growth model shows good correlation with observed All-India yields (0.7) with lower correlations for the irrigated wheat and rice crops (0.4). The difference in correlation is because irrigation provides a buffer against climate conditions, so that rainfed crop growth is more tied to climate than irrigated crop growth. The irrigation water demands induce hydrologic water stress in significant parts of the region, particularly in the Indus, with the streamflow unable to meet the irrigation demands. Although rainfall can vary significantly in south Asia, we find that water scarcity is largely chronic due to the irrigation demands rather than being intermittent due to climate variability.
A Growth Model of Inflation, Tax Evasion and Financial Repression
Roubini, Nouriel; Sala-i-Martin, Xavier
1992-01-01
In this paper we study the effects of policies of financial repression on long term growth and try to explain why optimizing governments might want to repress the financial sector. We also explain why inflation may be negatively related to growth, even though it does not affect growth directly. We argue that the main reason why governments repress the financial sector is that this sector is the source of "easy" resources for the public budget The source of revenue stemming from this intervent...
A local cellular model for growth on quasicrystals
International Nuclear Information System (INIS)
Chidyagwai, Prince; Reiter, Clifford A.
2005-01-01
The growth of real valued cellular automata using a deterministic algorithm on 2-dimensional quasicrystalline structures is investigated. Quasicrystals are intermediate between the rigid organization of crystals and disorganized random structures. Since the quasicrystalline structures may be highly symmetric or not, we are able to obtain highly organized and relatively random growth patterns. This deterministic growth produces dendrite, sector, stellar, regular polygons, round, and random DLA-like structures
The impact of remittances on economic growth: An econometric model
Directory of Open Access Journals (Sweden)
Dietmar Meyer
2017-05-01
In other words, the econometric analysis will be based on those six remittance receiving countries. The paper is then to review the empirical literature devoted to the impact of remittances on economic growth, in order, to identify empirically if there are significant relationships between remittances and growth in these countries. The results suggest that remittances have a positive impact on growth and that this impact increases at higher levels of remittances relative to GDP.
Wood, Phillip Karl; Jackson, Kristina M
2013-08-01
Researchers studying longitudinal relationships among multiple problem behaviors sometimes characterize autoregressive relationships across constructs as indicating "protective" or "launch" factors or as "developmental snares." These terms are used to indicate that initial or intermediary states of one problem behavior subsequently inhibit or promote some other problem behavior. Such models are contrasted with models of "general deviance" over time in which all problem behaviors are viewed as indicators of a common linear trajectory. When fit of the "general deviance" model is poor and fit of one or more autoregressive models is good, this is taken as support for the inhibitory or enhancing effect of one construct on another. In this paper, we argue that researchers consider competing models of growth before comparing deviance and time-bound models. Specifically, we propose use of the free curve slope intercept (FCSI) growth model (Meredith & Tisak, 1990) as a general model to typify change in a construct over time. The FCSI model includes, as nested special cases, several statistical models often used for prospective data, such as linear slope intercept models, repeated measures multivariate analysis of variance, various one-factor models, and hierarchical linear models. When considering models involving multiple constructs, we argue the construct of "general deviance" can be expressed as a single-trait multimethod model, permitting a characterization of the deviance construct over time without requiring restrictive assumptions about the form of growth over time. As an example, prospective assessments of problem behaviors from the Dunedin Multidisciplinary Health and Development Study (Silva & Stanton, 1996) are considered and contrasted with earlier analyses of Hussong, Curran, Moffitt, and Caspi (2008), which supported launch and snare hypotheses. For antisocial behavior, the FCSI model fit better than other models, including the linear chronometric growth curve
International Nuclear Information System (INIS)
Eby, Wayne M; Tabatabai, Mohammad A; Bursac, Zoran
2010-01-01
An understanding of growth dynamics of tumors is important in understanding progression of cancer and designing appropriate treatment strategies. We perform a comparative study of the hyperbolastic growth models with the Weibull and Gompertz models, which are prevalently used in the field of tumor growth. The hyperbolastic growth models H1, H2, and H3 are applied to growth of solid Ehrlich carcinoma under several different treatments. These are compared with results from Gompertz and Weibull models for the combined treatment. The growth dynamics of the solid Ehrlich carcinoma with the combined treatment are studied using models H1, H2, and H3, and the models are highly accurate in representing the growth. The growth dynamics are also compared with the untreated tumor, the tumor treated with only iodoacetate, and the tumor treated with only dimethylsulfoxide, and the combined treatment. The hyperbolastic models prove to be effective in representing and analyzing the growth dynamics of the solid Ehrlich carcinoma. These models are more precise than Gompertz and Weibull and show less error for this data set. The precision of H3 allows for its use in a comparative analysis of tumor growth rates between the various treatments
Integrated healthcare networks' performance: a growth curve modeling approach.
Wan, Thomas T H; Wang, Bill B L
2003-05-01
This study examines the effects of integration on the performance ratings of the top 100 integrated healthcare networks (IHNs) in the United States. A strategic-contingency theory is used to identify the relationship of IHNs' performance to their structural and operational characteristics and integration strategies. To create a database for the panel study, the top 100 IHNs selected by the SMG Marketing Group in 1998 were followed up in 1999 and 2000. The data were merged with the Dorenfest data on information system integration. A growth curve model was developed and validated by the Mplus statistical program. Factors influencing the top 100 IHNs' performance in 1998 and their subsequent rankings in the consecutive years were analyzed. IHNs' initial performance scores were positively influenced by network size, number of affiliated physicians and profit margin, and were negatively associated with average length of stay and technical efficiency. The continuing high performance, judged by maintaining higher performance scores, tended to be enhanced by the use of more managerial or executive decision-support systems. Future studies should include time-varying operational indicators to serve as predictors of network performance.
McLane, Sierra C; LeMay, Valerie M; Aitken, Sally N
2011-04-01
Forests strongly affect Earth's carbon cycles, making our ability to forecast forest-productivity changes associated with rising temperatures and changes in precipitation increasingly critical. In this study, we model the influence of climate on annual radial growth using lodgepole pine (Pinus contorta) trees grown for 34 years in a large provenance experiment in western Canada. We use a random-coefficient modeling approach to build universal growth-trend response functions that simultaneously incorporate the impacts of different provenance and site climates on radial growth trends under present and future annual (growth-year), summer, and winter climate regimes. This approach provides new depth to traditional quantitative genetics population response functions by illustrating potential changes in population dominance over time, as well as indicating the age and size at which annual growth begins declining for any population growing in any location under any present or future climate scenario within reason, given the ages and climatic conditions sampled. Our models indicate that lodgepole pine radial-growth levels maximize between 3.9 degrees and 5.1 degrees C mean growth-year temperature. This translates to productivity declining by the mid-21st century in southern and central British Columbia (BC), while increasing beyond the 2080s in northern BC and Yukon, as temperatures rise. Relative to summer climate indices, productivity is predicted to decline continuously through the 2080s in all locations, while relative to winter climate variables, the opposite trend occurs, with the growth increases caused by warmer winters potentially offsetting the summer losses. Trees from warmer provenances, i.e., from the center of the species range, perform best in nearly all of our present and future climate-scenario models. We recommend that similar models be used to analyze population growth trends relative to annual and intra-annual climate in other large-scale provenance
Modeling economic growth fuelled by science and technology
Directory of Open Access Journals (Sweden)
Leonardo Costa Ribeiro
2010-06-01
Full Text Available This paper suggests a simulation model to investigate how science and technology fuel economic growth. This model is built upon a synthesis of technological capabilities represented by national innovation systems. This paper gathers data of papers and patents for 183 countries between 1999 and 2003, as well as GDP and population for 2003. These data show a strong correlation between science, technology and income. Three simulation exercises are performed. Feeding our algorithm with data for population, patents and scientific papers, we obtain the world income distribution. These results support our conjecture on the role of science and technology as sources of the wealth of nations.Este artigo propõe um modelo de simulação para investigar a contribuição da ciência e da tecnologia para o crescimento econômico. O ponto de partida são os sistemas nacionais de inovação, um conceito que sintetiza a capacitação tecnológica das nações. Desta forma, o modelo pode preservar simplicidade e parcimônia. Os dados coletados (patentes, artigos e PIB e população, para 183 países indicam uma forte correlação entre ciência, tecnologia e renda. Três exercícios com simulações são realizados para diversos momentos do tempo, mostrando a progressiva aderência do modelo a essas variáveis tecnológicas.
Piecewise Linear-Linear Latent Growth Mixture Models with Unknown Knots
Kohli, Nidhi; Harring, Jeffrey R.; Hancock, Gregory R.
2013-01-01
Latent growth curve models with piecewise functions are flexible and useful analytic models for investigating individual behaviors that exhibit distinct phases of development in observed variables. As an extension of this framework, this study considers a piecewise linear-linear latent growth mixture model (LGMM) for describing segmented change of…
Connor W. Barth; Susan E. Meyer; Julie Beckstead; Phil S. Allen
2015-01-01
Population-based threshold models using hydrothermal time (HTT) have been widely used to model seed germination. We used HTT to model conidial germination and mycelial growth for the seed pathogen Pyrenophora semeniperda in a novel approach to understanding its interactions with host seeds. Germination time courses and mycelial growth rates for P.semeniperda were...
Photosynthesis driven crop growth models for greenhouse cultivation; advances and bottlenecks.
Challa, H.; Heuvelink, E.
1996-01-01
In recent years considerable progress has been made in modelling growth of green-house crops. Nevertheless, the share of research in this field compared to crop modelling in general is only a few percent. Yet, crop growth models have a great potential for greenhouse production systems, because they
Optimal Operational Monetary Policy Rules in an Endogenous Growth Model: a calibrated analysis
Arato, Hiroki
2009-01-01
This paper constructs an endogenous growth New Keynesian model and considers growth and welfare effect of Taylor-type (operational) monetary policy rules. The Ramsey equilibrium and optimal operational monetary policy rule is also computed. In the calibrated model, the Ramseyoptimal volatility of inflation rate is smaller than that in standard exogenous growth New Keynesian model with physical capital accumulation. Optimal operational monetary policy rule makes nominal interest rate respond s...
Wei-Bin ZHANG
2017-01-01
This study examines economic growth and population change with discrimination against women in the labor market within the analytical framework of Solow’s neoclassical growth model. The study models dynamic interactions between wealth accumulation, time distribution between work, children caring, and leisure, population change with endogenous birth and mortality rates with gender discrimination. The production technology and markets are built on Solow’s neoclassical growth model. The basic me...
Revisiting a model of ontogenetic growth: estimating model parameters from theory and data.
Moses, Melanie E; Hou, Chen; Woodruff, William H; West, Geoffrey B; Nekola, Jeffery C; Zuo, Wenyun; Brown, James H
2008-05-01
The ontogenetic growth model (OGM) of West et al. provides a general description of how metabolic energy is allocated between production of new biomass and maintenance of existing biomass during ontogeny. Here, we reexamine the OGM, make some minor modifications and corrections, and further evaluate its ability to account for empirical variation on rates of metabolism and biomass in vertebrates both during ontogeny and across species of varying adult body size. We show that the updated version of the model is internally consistent and is consistent with other predictions of metabolic scaling theory and empirical data. The OGM predicts not only the near universal sigmoidal form of growth curves but also the M(1/4) scaling of the characteristic times of ontogenetic stages in addition to the curvilinear decline in growth efficiency described by Brody. Additionally, the OGM relates the M(3/4) scaling across adults of different species to the scaling of metabolic rate across ontogeny within species. In providing a simple, quantitative description of how energy is allocated to growth, the OGM calls attention to unexplained variation, unanswered questions, and opportunities for future research.
Calcite growth kinetics: Modeling the effect of solution stoichiometry
Wolthers, M.; Nehrke, G.; Gustafsson, J.P.; Van Cappellen, P.
2012-01-01
Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth
Microalgae bulk growth model with application to industrial scale systems
Quinn, J.; Winter, de L.; Bradley, T.
2011-01-01
The scalability of microalgae growth systems is a primary research topic in anticipation of the commercialization of microalgae-based biofuels. To date, there is little published data on the productivity of microalgae in growth systems that are scalable to commercially viable footprints. To inform
4D Shape-Preserving Modelling of Bone Growth
DEFF Research Database (Denmark)
Andresen, Per Rønsholt; Nielsen, Mads; Kreiborg, Sven
1998-01-01
From a set of temporally separated scannings of the same anatomical structure we wish to identify and analyze the growth in terms of a metamorphosis. That is, we study the tempral change of shape which may prowide an understanding of the biological processes which govern the growth process. We...
Multiscale modeling of submonolayer growth for Fe/Mo(110)
Czech Academy of Sciences Publication Activity Database
Mašín, Martin; Kotrla, Miroslav; Yang, B.; Asta, M.; Jahma, M.O.; Ala-Nissila, T.
2013-01-01
Roč. 86, č. 8 (2013), s. 359-365 ISSN 1434-6028 R&D Projects: GA ČR GA202/09/0775 Institutional support: RVO:68378271 Keywords : Monte Carlo simulations * kinetic rate equations * total energy calculations * epitaxial growth * cluster diffusion * island growth Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.463, year: 2013
Numerical simulation of brain tumor growth model using two-stage ...
African Journals Online (AJOL)
In the recent years, the study of glioma growth to be an active field of research Mathematical models that describe the proliferation and diffusion properties of the growth have been developed by many researchers. In this work, the performance analysis of two-stage Gauss-Seidel (TSGS) method to solve the glioma growth ...
A nonlinear model for surface segregation and solute trapping during planar film growth
International Nuclear Information System (INIS)
Han, Xiaoying; Spencer, Brian J.
2007-01-01
Surface segregation and solute trapping during planar film growth is one of the important issues in molecular beam epitaxy, yet the study on surface composition has been largely restricted to experimental work. This paper introduces some mathematical models of surface composition during planar film growth. Analytical solutions are obtained for the surface composition during growth
Modelling and predicting growth of psycrotolerant pseudomonads in milk and cottage cheese
DEFF Research Database (Denmark)
Martinez Rios, Veronica; Østergaard, Nina Bjerre; Rosshaug, Per Sand
2015-01-01
Introduction: Predictive food microbiology models have the potential to evaluate the effect of temperature on microbial growth during distribution as well as be used to determine how product characteristics can be modified to reduce growth to an acceptable level. Methods: Growth kinetics of psych...
Innovation, Decentralization, and Planning in a Multi-Region Model of Schumpeterian Economic Growth
Batabyal, Amit; Nijkamp, Peter
2014-01-01
We study innovation and the resulting Schumpeterian economic growth that this innovation gives rise to in a model with N heterogeneous regions. For each region i where i=1,...,N, our analysis leads to five findings. First, we define the balanced growth path (BGP) allocations and the equilibrium of interest. Second, we stipulate the form of the innovation possibilities frontier that is consistent with balanced economic growth. Third, we derive the growth rate of the ith region in the decentral...
Declining Radial Growth Response of Coastal Forests to Hurricanes and Nor'easters
Fernandes, Arnold; Rollinson, Christine R.; Kearney, William S.; Dietze, Michael C.; Fagherazzi, Sergio
2018-03-01
The Mid-Atlantic coastal forests in Virginia are stressed by episodic disturbance from hurricanes and nor'easters. Using annual tree ring data, we adopt a dendroclimatic and statistical modeling approach to understand the response and resilience of a coastal pine forest to extreme storm events, over the past few decades. Results indicate that radial growth of trees in the study area is influenced by age, regional climate trends, and individual tree effects but dominated periodically by growth disturbance due to storms. We evaluated seven local extreme storm events to understand the effect of nor'easters and hurricanes on radial growth. A general decline in radial growth was observed in the year of the extreme storm and 3 years following it, after which the radial growth started recovering. The decline in radial growth showed a statistically significant correlation with the magnitude of the extreme storm (storm surge height and wind speed). This study contributes to understanding declining tree growth response and resilience of coastal forests to past disturbances. Given the potential increase in hurricanes and storm surge severity in the region, this can help predict vegetation response patterns to similar disturbances in the future.
rights reserved Modelling Growth Kinetics of Klebsiella sp. FIRD 2
African Journals Online (AJOL)
ADOWIE PERE
... most toxic anthropogenic compounds deliberately introduced ... Due of its toxicity to marine organisms, the. International ... There are a lot of published papers describing ... The rate of bacterial growth and degradation can be represented as ...
Predicting growth of the healthy infant using a genome scale metabolic model.
Nilsson, Avlant; Mardinoglu, Adil; Nielsen, Jens
2017-01-01
An estimated 165 million children globally have stunted growth, and extensive growth data are available. Genome scale metabolic models allow the simulation of molecular flux over each metabolic enzyme, and are well adapted to analyze biological systems. We used a human genome scale metabolic model to simulate the mechanisms of growth and integrate data about breast-milk intake and composition with the infant's biomass and energy expenditure of major organs. The model predicted daily metabolic fluxes from birth to age 6 months, and accurately reproduced standard growth curves and changes in body composition. The model corroborates the finding that essential amino and fatty acids do not limit growth, but that energy is the main growth limiting factor. Disruptions to the supply and demand of energy markedly affected the predicted growth, indicating that elevated energy expenditure may be detrimental. The model was used to simulate the metabolic effect of mineral deficiencies, and showed the greatest growth reduction for deficiencies in copper, iron, and magnesium ions which affect energy production through oxidative phosphorylation. The model and simulation method were integrated to a platform and shared with the research community. The growth model constitutes another step towards the complete representation of human metabolism, and may further help improve the understanding of the mechanisms underlying stunting.
DEFF Research Database (Denmark)
Jensen, Morten B; Guldberg, Trine L; Harbøll, Anja
2017-01-01
the microscopic tumor cell spread. Gliomas favor spread along the white matter fiber tracts. Tumor growth models incorporating the MRI diffusion tensors (DTI) allow to account more consistently for the glioma growth. The aim of the study was to investigate the potential of a DTI driven growth model to improve...... target definition in glioblastoma (GBM). MATERIAL AND METHODS: Eleven GBM patients were scanned using T1w, T2w FLAIR, T1w + Gd and DTI. The brain was segmented into white matter, gray matter and cerebrospinal fluid. The Fisher-Kolmogorov growth model was used assuming uniform proliferation...
Predicting the peak growth velocity in the individual child: validation of a new growth model.
Busscher, I.; Kingma, I.; de Bruin, R.; Wapstra, F.H.; Verkerke, G.J.; Veldhuizen, A.G.
2012-01-01
Predicting the peak growth velocity in an individual patient with adolescent idiopathic scoliosis is essential or determining the prognosis of the disorder and timing of the (surgical) treatment. Until the present time, no accurate method has been found to predict the timing and magnitude of the
Predicting the peak growth velocity in the individual child : validation of a new growth model
Busscher, Iris; Kingma, Idsart; de Bruin, Rob; Wapstra, Frits Hein; Verkerke, Gijsvertus J.; Veldhuizen, Albert G.
Predicting the peak growth velocity in an individual patient with adolescent idiopathic scoliosis is essential or determining the prognosis of the disorder and timing of the (surgical) treatment. Until the present time, no accurate method has been found to predict the timing and magnitude of the
Predicting the peak growth velocity in the individual child: validation of a new growth model
Busscher, I.; Kingma, I.; Bruin, R.; Wapstra, F.H.; Verkerke, Gijsbertus Jacob; Veldhuizen, A.G.
2012-01-01
Predicting the peak growth velocity in an individual patient with adolescent idiopathic scoliosis is essential or determining the prognosis of the disorder and timing of the (surgical) treatment. Until the present time, no accurate method has been found to predict the timing and magnitude of the
Modeling salt movement and halophytic crop growth on marginal lands with the APEX model
Goehring, N.; Saito, L.; Verburg, P.; Jeong, J.; Garrett, A.
2016-12-01
Saline soils negatively impact crop productivity in nearly 20% of irrigated agricultural lands worldwide. At these saline sites, cultivation of highly salt-tolerant plants, known as halophytes, may increase productivity compared to conventional salt-sensitive crops (i.e., glycophytes), thereby increasing the economic potential of marginal lands. Through a variety of mechanisms, halophytes are more effective than glycophytes at excluding, accumulating, and secreting salts from their tissues. Each mechanism can have a different impact on the salt balance in the plant-soil-water system. To date, little information is available to understand the long-term impacts of halophyte cultivation on environmental quality. This project utilizes the Agricultural Policy/Environmental Extender (APEX) model, developed by the US Department of Agriculture, to model the growth and production of two halophytic crops. The crops being modeled include quinoa (Chenopodium quinoa), which has utilities for human consumption and forage, and AC Saltlander green wheatgrass (Elymus hoffmannii), which has forage utility. APEX simulates salt movement between soil layers and accounts for the salt balance in the plant-soil-water system, including salinity in irrigation water and crop-specific salt uptake. Key crop growth parameters in APEX are derived from experimental growth data obtained under non-stressed conditions. Data from greenhouse and field experiments in which quinoa and AC Saltlander were grown under various soil salinity and irrigation salinity treatments are being used to parameterize, calibrate, and test the model. This presentation will discuss progress on crop parameterization and completed model runs under different salt-affected soil and irrigation conditions.
International Nuclear Information System (INIS)
Kamaya, Masayuki; Kawakubo, Masahiro
2012-01-01
In this study, the fatigue damage was assumed to be equivalent to the crack initiation and its growth, and fatigue life was assessed by predicting the crack growth. First, a low-cycle fatigue test was conducted in air at room temperature under constant cyclic strain range of 1.2%. The crack initiation and change in crack size during the test were examined by replica investigation. It was found that a crack of 41.2 μm length was initiated almost at the beginning of the test. The identified crack growth rate was shown to correlate well with the strain intensity factor, whose physical meaning was discussed in this study. The fatigue life prediction model (equation) under constant strain range was derived by integrating the crack growth equation defined using the strain intensity factor, and the predicted fatigue lives were almost identical to those obtained by low-cycle fatigue tests. The change in crack depth predicted by the equation also agreed well with the experimental results. Based on the crack growth prediction model, it was shown that the crack size would be less than 0.1 mm even when the estimated fatigue damage exceeded the critical value of the design fatigue curve, in which a twenty-fold safety margin was used for the assessment. It was revealed that the effect of component size and surface roughness, which have been investigated empirically by fatigue tests, could be reasonably explained by considering the crack initiation and growth. Furthermore, the environmental effect on the fatigue life was shown to be brought about by the acceleration of crack growth. (author)
Defining old growth for fire-adapted forests of the Western United States
Merrill R. Kaufmann; Daniel Binkley; Peter Z. Fule; Johnson Marlin; Scott L. Stephens; Thomas W. Swetnam
2007-01-01
There are varying definitions of old-growth forests because of differences in environment and differing fire influence across the Intermountain West. Two general types of forests reflect the role of fire: 1) forests shaped by natural changes in structure and species makeup-plant succession-that are driven by competitive differences among species and individual trees...
Modelling the growth of Populus species using Ecosystem Demography (ED) model
Wang, D.; Lebauer, D. S.; Feng, X.; Dietze, M. C.
2010-12-01
Hybrid poplar plantations are an important source being evaluated for biomass production. Effective management of such plantations requires adequate growth and yield models. The Ecosystem Demography model (ED) makes predictions about the large scales of interest in above- and belowground ecosystem structure and the fluxes of carbon and water from a description of the fine-scale physiological processes. In this study, we used a workflow management tool, the Predictive Ecophysiological Carbon flux Analyzer (PECAn), to integrate literature data, field measurement and the ED model to provide predictions of ecosystem functioning. Parameters for the ED ensemble runs were sampled from the posterior distribution of ecophysiological traits of Populus species compiled from the literature using a Bayesian meta-analysis approach. Sensitivity analysis was performed to identify the parameters which contribute the most to the uncertainties of the ED model output. Model emulation techniques were used to update parameter posterior distributions using field-observed data in northern Wisconsin hybrid poplar plantations. Model results were evaluated with 5-year field-observed data in a hybrid poplar plantation at New Franklin, MO. ED was then used to predict the spatial variability of poplar yield in the coterminous United States (United States minus Alaska and Hawaii). Sensitivity analysis showed that root respiration, dark respiration, growth respiration, stomatal slope and specific leaf area contribute the most to the uncertainty, which suggests that our field measurements and data collection should focus on these parameters. The ED model successfully captured the inter-annual and spatial variability of the yield of poplar. Analyses in progress with the ED model focus on evaluating the ecosystem services of short-rotation woody plantations, such as impacts on soil carbon storage, water use, and nutrient retention.
A review on pipeline corrosion, in-line inspection (ILI), and corrosion growth rate models
International Nuclear Information System (INIS)
Vanaei, H.R.; Eslami, A.; Egbewande, A.
2017-01-01
Pipelines are the very important energy transmission systems. Over time, pipelines can corrode. While corrosion could be detected by in-line inspection (ILI) tools, corrosion growth rate prediction in pipelines is usually done through corrosion rate models. For pipeline integrity management and planning selecting the proper corrosion ILI tool and also corrosion growth rate model is important and can lead to significant savings and safer pipe operation. In this paper common forms of pipeline corrosion, state of the art ILI tools, and also corrosion growth rate models are reviewed. The common forms of pipeline corrosion introduced in this paper are Uniform/General Corrosion, Pitting Corrosion, Cavitation and Erosion Corrosion, Stray Current Corrosion, Micro-Bacterial Influenced Corrosion (MIC). The ILI corrosion detection tools assessed in this study are Magnetic Flux Leakage (MFL), Circumferential MFL, Tri-axial MFL, and Ultrasonic Wall Measurement (UT). The corrosion growth rate models considered in this study are single-value corrosion rate model, linear corrosion growth rate model, non-linear corrosion growth rate model, Monte-Carlo method, Markov model, TD-GEVD, TI-GEVD model, Gamma Process, and BMWD model. Strengths and limitations of ILI detection tools, and also corrosion predictive models with some practical examples are discussed. This paper could be useful for those whom are supporting pipeline integrity management and planning. - Highlights: • Different forms of pipeline corrosion are explained. • Common In-Line Inspection (ILI) tools and corrosion growth rate models are introduced. • Strength and limitations of corrosion growth rate models/ILI tools are discussed. • For pipeline integrity management programs using more than one corrosion growth rate model/ILI tool is suggested.
Evaluation of HIV Risk Reduction and Intervention Programs via Latent Growth Model.
Wang, Jichuan; Siegal, Harvey A.; Falck, Russel S.; Carlson, Robert G.; Rahman, Ahmmed
1999-01-01
Demonstrates how the latent growth model can be applied to the evaluation of programs targeting HIV risk behavior among drug users. Multigroup piecewise latent growth models were fit to longitudinal data with three repeated response measures. Participants were 430 drug users and their sex partners. (SLD)
Modelling and predicting growth of psychrotolerant pseudomonads in milk and cottage cheese
DEFF Research Database (Denmark)
Martinez Rios, Veronica; Østergaard, Nina Bjerre; Gkogka, Elissavet
2016-01-01
Mathematical models were developed and evaluated for growth of psychrotolerant pseudomonads in chilled milk and in cottage cheese with cultured cream dressing. The mathematical models include the effect of temperature, pH, NaCl, lactic acid and sorbic acid. A simplified cardinal parameter growth ...
Modelling and predicting growth of psychrotolerant pseudomonads in milk and cottage cheese
DEFF Research Database (Denmark)
Martinez Rios, Veronica; Østergaard, Nina Bjerre; Rosshaug, Per Sand
Mathematical models were developed and evaluated for growth of psychrotolerant pseudomonads in chilled milk and cottage cheese with cultured cream dressing. The mathematical models include the effect of temperature, pH, NaCl, lactic acid and sorbic acid. A simplified cardinal parameter growth mod...
Analytical prediction model for non-symmetric fatigue crack growth in Fibre Metal Laminates
Wang, W.; Rans, C.D.; Benedictus, R.
2017-01-01
This paper proposes an analytical model for predicting the non-symmetric crack growth and accompanying delamination growth in FMLs. The general approach of this model applies Linear Elastic Fracture Mechanics, the principle of superposition, and displacement compatibility based on the
International Nuclear Information System (INIS)
Lou, C.
2002-01-01
An advection-diffusion model has been set up to describe normal grain growth. In this model grains are divided into different groups according to their topological classes (number of sides of a grain). Topological transformations are modelled by advective and diffusive flows governed by advective and diffusive coefficients respectively, which are assumed to be proportional to topological classes. The ordinary differential equations governing self-similar time-independent grain size distribution can be derived analytically from continuity equations. It is proved that the time-independent distributions obtained by solving the ordinary differential equations have the same form as the time-dependent distributions obtained by solving the continuity equations. The advection-diffusion model is extended to describe the stagnation of normal grain growth in thin films. Grain boundary grooving prevents grain boundaries from moving, and the correlation between neighbouring grains accelerates the stagnation of normal grain growth. After introducing grain boundary grooving and the correlation between neighbouring grains into the model, the grain size distribution is close to a lognormal distribution, which is usually found in experiments. A vertex computer simulation of normal grain growth has also been carried out to make a cross comparison with the advection-diffusion model. The result from the simulation did not verify the assumption that the advective and diffusive coefficients are proportional to topological classes. Instead, we have observed that topological transformations usually occur on certain topological classes. This suggests that the advection-diffusion model can be improved by making a more realistic assumption on topological transformations. (author)
An endogenous growth model with embodied energy-saving technical change
International Nuclear Information System (INIS)
Van Zon, A.; Yetkiner, I. H.
2003-01-01
In this paper, we extend the Romer [Journal of Political Economy 98 (Part 2) (1990) S271] model in two ways. First we include energy consumption of intermediates. Second, intermediates become heterogeneous due to endogenous energy-saving technical change. We show that the resulting model can still generate steady state growth, but the growth rate depends negatively on the growth of real energy prices. The reason is that real energy price rises will lower the profitability of using new intermediate goods, and hence, the profitability of doing research, and therefore have a negative impact on growth. We also show that the introduction of an energy tax that is recycled in the form of an R and D subsidy may increase growth. We conclude that in order to have energy efficiency growth and output growth under rising real energy prices, a combination of R and D and energy policy is called for
A generalized-growth model to characterize the early ascending phase of infectious disease outbreaks
DEFF Research Database (Denmark)
Viboud, Cecile; Simonsen, Lone; Chowell, Gerardo
2016-01-01
the importance of sub-exponential growth for forecasting purposes.Results: We applied the generalized-growth model to 20 infectious disease outbreaks representing a range of transmission routes. We uncovered epidemic profiles ranging from very slow growth (p = 0.14 for the Ebola outbreak in Bomi, Liberia (2014...... African Ebola epidemic provided a unique opportunity to explore how growth profiles vary by geography; analysis of the largest district-level outbreaks revealed substantial growth variations (mean p = 0.59, range: 0.14–0.97). The districts of Margibi in Liberia and Bombali and Bo in Sierra Leone had near......-exponential growth, while the districts of Bomi in Liberia and Kenema in Sierra Leone displayed near constant incidences.Conclusions: Our findings reveal significant variation in epidemic growth patterns across different infectious disease outbreaks and highlights that sub-exponential growth is a common phenomenon...
DEFF Research Database (Denmark)
Nielsen, Cecilie Lykke Marvig; Kristiansen, Rikke M.; Nielsen, Dennis Sandris
2015-01-01
sugar and fat and a traditionally long self-life of sweet IMFs, the presence of Z. rouxii in the raw materials for IMFs has made assessment of the microbiological stability a significant hurdle in product development. Therefore, knowledge on growth/no growth boundaries of Z. rouxii in sweet IMFs...... is important to ensure microbiological stability and aid product development. Several models have been developed for fat based, sweet IMFs. However, fruit/sugar based IMFs, such as fruit based chocolate fillings and jams, have lower pH and aw than what is accounted for in previously developed models....... In the present study growth/no growth models for acidified sweet IMFs were developed with the variables aw (0.65-0.80), pH (2.5-4.0), ethanol (0-14.5% (w/w) in water phase) and time (0-90 days). Two different strains of Z. rouxii previously found to show pronounced resistance to the investigated variables were...
Directory of Open Access Journals (Sweden)
Uri Barenholz
Full Text Available Most proteins show changes in level across growth conditions. Many of these changes seem to be coordinated with the specific growth rate rather than the growth environment or the protein function. Although cellular growth rates, gene expression levels and gene regulation have been at the center of biological research for decades, there are only a few models giving a base line prediction of the dependence of the proteome fraction occupied by a gene with the specific growth rate. We present a simple model that predicts a widely coordinated increase in the fraction of many proteins out of the proteome, proportionally with the growth rate. The model reveals how passive redistribution of resources, due to active regulation of only a few proteins, can have proteome wide effects that are quantitatively predictable. Our model provides a potential explanation for why and how such a coordinated response of a large fraction of the proteome to the specific growth rate arises under different environmental conditions. The simplicity of our model can also be useful by serving as a baseline null hypothesis in the search for active regulation. We exemplify the usage of the model by analyzing the relationship between growth rate and proteome composition for the model microorganism E.coli as reflected in recent proteomics data sets spanning various growth conditions. We find that the fraction out of the proteome of a large number of proteins, and from different cellular processes, increases proportionally with the growth rate. Notably, ribosomal proteins, which have been previously reported to increase in fraction with growth rate, are only a small part of this group of proteins. We suggest that, although the fractions of many proteins change with the growth rate, such changes may be partially driven by a global effect, not necessarily requiring specific cellular control mechanisms.
United States geological survey's reserve-growth models and their implementation
Klett, T.R.
2005-01-01
The USGS has developed several mathematical models to forecast reserve growth of fields both in the United States (U.S.) and the world. The models are based on historical reserve growth patterns of fields in the U.S. The patterns of past reserve growth are extrapolated to forecast future reserve growth. Changes of individual field sizes through time are extremely variable, therefore, the reserve growth models take on a statistical approach whereby volumetric changes for populations of fields are used in the models. Field age serves as a measure of the field-development effort that is applied to promote reserve growth. At the time of the USGS World Petroleum Assessment 2000, a reserve growth model for discovered fields of the world was not available. Reserve growth forecasts, therefore, were made based on a model of historical reserve growth of fields of the U.S. To test the feasibility of such an application, reserve growth forecasts were made of 186 giant oil fields of the world (excluding the U.S. and Canada). In addition, forecasts were made for these giant oil fields subdivided into those located in and outside of Organization of Petroleum Exporting Countries (OPEC). The model provided a reserve-growth forecast that closely matched the actual reserve growth that occurred from 1981 through 1996 for the 186 fields as a whole, as well as for both OPEC and non-OPEC subdivisions, despite the differences in reserves definition among the fields of the U.S. and the rest of the world. ?? 2005 International Association for Mathematical Geology.
A stress driven growth model for soft tissue considering biological availability
International Nuclear Information System (INIS)
Oller, S; Bellomo, F J; Nallim, L G; Armero, F
2010-01-01
Some of the key factors that regulate growth and remodeling of tissues are fundamentally mechanical. However, it is important to take into account the role of bioavailability together with the stresses and strains in the processes of normal or pathological growth. In this sense, the model presented in this work is oriented to describe the growth of soft biological tissue under 'stress driven growth' and depending on the biological availability of the organism. The general theoretical framework is given by a kinematic formulation in large strain combined with the thermodynamic basis of open systems. The formulation uses a multiplicative decomposition of deformation gradient, splitting it in a growth part and visco-elastic part. The strains due to growth are incompatible and are controlled by an unbalanced stresses related to a homeostatic state. Growth implies a volume change with an increase of mass maintaining constant the density. One of the most interesting features of the proposed model is the generation of new tissue taking into account the contribution of mass to the system controlled through biological availability. Because soft biological tissues in general have a hierarchical structure with several components (usually a soft matrix reinforced with collagen fibers), the developed growth model is suitable for the characterization of the growth of each component. This allows considering a different behavior for each of them in the context of a generalized theory of mixtures. Finally, we illustrate the response of the model in case of growth and atrophy with an application example.
Hunt, Shelby D.
2012-01-01
Foss (2012) provides an informed and informative comment on my article “Trust, Personal Moral Codes, and the Resource-Advantage Theory of Competition: Explaining Productivity, Economic Growth, and Wealth Creation” (Hunt, 2012). In general, his comment is highly supportive of both the theory and the arguments developed in my article. He does, however, raise certain issues that need to be addressed. These issues relate to the concept of total factor productivity, the role of institutions in pro...
Cellular Automaton Modeling of Dendritic Growth Using a Multi-grid Method
International Nuclear Information System (INIS)
Natsume, Y; Ohsasa, K
2015-01-01
A two-dimensional cellular automaton model with a multi-grid method was developed to simulate dendritic growth. In the present model, we used a triple-grid system for temperature, solute concentration and solid fraction fields as a new approach of the multi-grid method. In order to evaluate the validity of the present model, we carried out simulations of single dendritic growth, secondary dendrite arm growth, multi-columnar dendritic growth and multi-equiaxed dendritic growth. From the results of the grid dependency from the simulation of single dendritic growth, we confirmed that the larger grid can be used in the simulation and that the computational time can be reduced dramatically. In the simulation of secondary dendrite arm growth, the results from the present model were in good agreement with the experimental data and the simulated results from a phase-field model. Thus, the present model can quantitatively simulate dendritic growth. From the simulated results of multi-columnar and multi-equiaxed dendrites, we confirmed that the present model can perform simulations under practical solidification conditions. (paper)
Modelling the growth of Listeria monocytogenes on the surface of smear- or mould-ripened cheese
Directory of Open Access Journals (Sweden)
Sol eSchvartzman
2014-07-01
Full Text Available Surface-ripened cheeses are matured by means of manual or mechanical technologies posing a risk of cross-contamination, if any cheeses are contaminated with Listeria monocytogenes. In predictive microbiology, primary models are used to describe microbial responses, such as growth rate over time and secondary models explain how those responses change with environmental factors. In this way, primary models were used to assess the growth rate of L. monocytogenes during ripening of the cheeses and the secondary models to test how much the growth rate was affected by either the pH and/or the water activity (aw of the cheeses. The two models combined can be used to predict outcomes. The purpose of these experiments was to test three primary (the modified Gompertz equation, the Baranyi and Roberts model and the Logistic model and three secondary (the Cardinal model, the Ratowski model and the Presser model mathematical models in order to define which combination of models would best predict the growth of L. monocytogenes on the surface of artificially contaminated surface-ripened cheeses. Growth on the surface of the cheese was assessed and modelled. The primary models were firstly fitted to the data and the effects of pH and aw on the growth rate (μmax were incorporated and assessed one by one with the secondary models. The Logistic primary model by itself did not show a better fit of the data among the other primary models tested, but the inclusion of the Cardinal secondary model improved the final fit. The aw was not related to the growth of Listeria. This study suggests that surface-ripened cheese should be separately regulated within EU microbiological food legislation and results expressed as counts per surface area rather than per gram.
Modeling the growth of Listeria monocytogenes on the surface of smear- or mold-ripened cheese.
Schvartzman, M Sol; Gonzalez-Barron, Ursula; Butler, Francis; Jordan, Kieran
2014-01-01
Surface-ripened cheeses are matured by means of manual or mechanical technologies posing a risk of cross-contamination, if any cheeses are contaminated with Listeria monocytogenes. In predictive microbiology, primary models are used to describe microbial responses, such as growth rate over time and secondary models explain how those responses change with environmental factors. In this way, primary models were used to assess the growth rate of L. monocytogenes during ripening of the cheeses and the secondary models to test how much the growth rate was affected by either the pH and/or the water activity (aw) of the cheeses. The two models combined can be used to predict outcomes. The purpose of these experiments was to test three primary (the modified Gompertz equation, the Baranyi and Roberts model, and the Logistic model) and three secondary (the Cardinal model, the Ratowski model, and the Presser model) mathematical models in order to define which combination of models would best predict the growth of L. monocytogenes on the surface of artificially contaminated surface-ripened cheeses. Growth on the surface of the cheese was assessed and modeled. The primary models were firstly fitted to the data and the effects of pH and aw on the growth rate (μmax) were incorporated and assessed one by one with the secondary models. The Logistic primary model by itself did not show a better fit of the data among the other primary models tested, but the inclusion of the Cardinal secondary model improved the final fit. The aw was not related to the growth of Listeria. This study suggests that surface-ripened cheese should be separately regulated within EU microbiological food legislation and results expressed as counts per surface area rather than per gram.
MODELING OF INTERACTION LAYER GROWTH BETWEEN U-Mo PARTICLES AND AN Al MATRIX
YEON SOO KIM; G.L. HOFMAN; HO JIN RYU; JONG MAN PARK; A.B. ROBINSON; D.M. WACHS
2013-01-01
Interaction layer growth between U-Mo alloy fuel particles and Al in a dispersion fuel is a concern due to the volume expansion and other unfavorable irradiation behavior of the interaction product. To reduce interaction layer (IL) growth, a small amount of Si is added to the Al. As a result, IL growth is affected by the Si content in the Al matrix. In order to predict IL growth during fabrication and irradiation, empirical models were developed. For IL growth prediction during fabrication an...
Natural Disasters in a Two-Sector Model of Endogenous Growth
Masako Ikefuji; Ryo Horii
2006-01-01
Using an endogenous growth model with physical and human capital accumulation, this paper considers the sustainability of economic growth when the use of a polluting input (e.g., fossil fuels) intensifies the risk of capital destruction through natural disasters. We find that growth is sustainable only if the tax rate on the polluting input increases over time. The long-term rate of economic growth follows an inverted V-shaped curve relative to the growth rate of the environmental tax, and it...
Growth theory after Keynes, part I: the unfortunate suppression of the Harrod-Domar model
Directory of Open Access Journals (Sweden)
Hendrik Van den Berg
2013-11-01
Full Text Available After Harrod and Domar independently developed a dynamic Keynesian circular flow model to illustrate the instability of a growing economy, mainstream economists quickly reduced their model to a supply side-only growth model, which they subsequently rejected as too simplistic and replaced with Solow’s neoclassical growth model. The rejection process of first diminishing the model and then replaced it with a neoclassical alternative was similar to how the full Keynesian macroeconomic paradigm was diminished into IS-LM analysis and then replaced by a simplistic neoclassical framework that largely ignored the demand side of the economy. Furthermore, subsequent work by mainstream economists has resulted in a logically inconsistent framework for analyzing economic growth; the popular endogenous growth models, which use Schumpeter’s concept of profit-driven creative destruction to explain the technological change that Solow left as exogenous, are not logically compatible with the Solow model.
A fuzzy mathematical model of West Java population with logistic growth model
Nurkholipah, N. S.; Amarti, Z.; Anggriani, N.; Supriatna, A. K.
2018-03-01
In this paper we develop a mathematics model of population growth in the West Java Province Indonesia. The model takes the form as a logistic differential equation. We parameterize the model using several triples of data, and choose the best triple which has the smallest Mean Absolute Percentage Error (MAPE). The resulting model is able to predict the historical data with a high accuracy and it also able to predict the future of population number. Predicting the future population is among the important factors that affect the consideration is preparing a good management for the population. Several experiment are done to look at the effect of impreciseness in the data. This is done by considering a fuzzy initial value to the crisp model assuming that the model propagates the fuzziness of the independent variable to the dependent variable. We assume here a triangle fuzzy number representing the impreciseness in the data. We found that the fuzziness may disappear in the long-term. Other scenarios also investigated, such as the effect of fuzzy parameters to the crisp initial value of the population. The solution of the model is obtained numerically using the fourth-order Runge-Kutta scheme.
An atomic-scale model of fcc crystal-growth
Energy Technology Data Exchange (ETDEWEB)
Waal, B.W. van de (Technische Hogeschool Twente, Enschede (Netherlands). Dept. of Physics)
1991-01-01
Nearly perfect fcc growth may be simulated by the application of a simple growth-algorithm - only sites that are at least 4-coordinated are occupied - to a selected seed. The seed is a 22-atom cluster, being the smallest close-packed structure with two crossing stacking-faults. The stacking-faults produce active surface-sites, that can not be exhausted by occupation; they are arranged in non-vanishing steps, similar to those produced by screw-dislocations. The algorithm prevents further stacking-faults, and ensures ABC-stacking of close-packed (111)-layers, characteristic of the fcc structure. The same algorithm would not produce further growth of perfect fcc clusters or of Mackay icosahedra. It is proposed that the ability to grow fast under near-equilibrium conditions is a better criterion to select clusters as precursors of the bulk-structure than their cohesive energy. The crystal structure problem of the rare gases - why fcc, not hcp - is discussed in connection with the apparent impossibility to simulate hcp growth by an analogous procedure. (orig.).
Specific and general human capital in an endogenous growth model
Czech Academy of Sciences Publication Activity Database
Jerbashian, Vahagn; Slobodyan, Sergey; Vourvachaki, E.
2015-01-01
Roč. 53, č. 3 (2015), s. 167-204 ISSN 0012-8775 R&D Projects: GA AV ČR IAA700850902 Institutional support: RVO:67985998 Keywords : economic growth * human capital types * education policy Subject RIV: AH - Economic s Impact factor: 0.404, year: 2015
Specific and general human capital in an endogenous growth model
Czech Academy of Sciences Publication Activity Database
Jerbashian, Vahagn; Slobodyan, Sergey; Vourvachaki, E.
2015-01-01
Roč. 53, č. 3 (2015), s. 167-204 ISSN 0012-8775 Institutional support: PRVOUK-P23 Keywords : economic growth * human capital types * education policy Subject RIV: AH - Economic s Impact factor: 0.404, year: 2015
Modeling elm growth and Dutch elm disease susceptibility
Alberto Santini; Luisa Ghelardini
2012-01-01
Elm susceptibility to Dutch elm disease (DED) displays strong seasonal variation. The period during which elms can become infected and express DED symptoms is generally restricted to several weeks after growth resumption in spring, although it can vary among species, provenances, and environmental conditions. The reason for this phenomenon is not understood, but the...
Fiscal Policy in a Stochastic Model of Endogenous Growth
Canton, E.J.F.
1997-01-01
It is nowadays widely believed that public schooling may contribute favourably to long-term economic growth. The income tax rates that are needed to finance government spending typically show an erratic time pattern. Such tax randomness could increase the intensity of the business cycle. Thus,
Cross-twinning model of fcc crystal growth
van de Waal, B.W.
1995-01-01
The theory developed in 1960 by Wagner, Hamilton and Seidensticker (WHS-theory) to explain observed crystal growth phenomena in Ge is critically reviewed and shown to be capable of explaining preservation of ABC stacking order in two dimensions in fcc crystals of effectively spherical closed shell
The current Russian model of social development, and economic growth
Directory of Open Access Journals (Sweden)
V V Paramonov
2016-12-01
Full Text Available Although the Article 7 of the Constitution of Russia adopted in 1993 defines the country as a social state, the contemporary social and economic situation is significantly different from this declaration. The author considers the current situation focusing on the foundations of the welfare state. The indicators of social inequality and stratification that allow to identify the country as a social state prove the widening gap between the rich and poor. In recent years, nothing has been done to achieve the more equitable distribution of income and national wealth, which led to the further growth of social inequality exceeding the global indices. The author believes that the high level of social inequality negatively affects the economic growth. Based on the studies of Russian scientists he concludes that equal distribution of income provides higher rates of economic growth and prosperity of the country. The modified theory of the factors of production explains this interconnection, and adds a few more factors, including such a specific resource as sales market, to three factors introduced by J.B. Say at the beginning of the XIX century. The huge social inequality and, consequently, a significant number of the poor deprive the country of such an important resource. To change the situation, the author proposes to return to the progressive tax scale and introduce the zero rate of income tax for the poorest groups in order to create prerequisites for the growth of consumer demand under the economic crisis.
Models of economic growth and development in the context of ...
African Journals Online (AJOL)
It is argued that a very necessary condition for growth and transformational development in Africa is heavy investment in human capital. It is pointed out that countries that invest much human capital to produce highly educated populaces usually reap the benefits of such in terms of high per capita GDPs, regardless of the ...
Literary Experience and Literature Teaching since the Growth Model
Reid, Ian
2016-01-01
By the late 70s the "growth through English" slogan, derived from John Dixon's account of the Dartmouth conference, had become popular around Australia. In 1980 the Sydney IFTE conference featured several Dartmouth veterans; but during that conference, Dartmouth-linked ideas from overseas mingled with lines of local influence, especially…
Growth and yield model application in tropical rain forest management
James Atta-Boateng; John W., Jr. Moser
2000-01-01
Analytical tools are needed to evaluate the impact of management policies on the sustainable use of rain forest. Optimal decisions concerning the level of management inputs require accurate predictions of output at all relevant input levels. Using growth data from 40 l-hectare permanent plots obtained from the semi-deciduous forest of Ghana, a system of 77 differential...
Modeling of thin films growth processes in the early stage for atoms with covalent bonds
International Nuclear Information System (INIS)
Tupik, V A; Margolin, V I; Su, Chu Trong
2017-01-01
Computer simulation for obtaining thin film’s growth process at an early stage with the proposed model of atoms with isotropic and anisotropic interactions been considered. Carrying out the procedure for analyzing the problem on the basis of the program being implemented, computer simulation of thin film growth processes has been carried out on several examples. The results of computer simulation of the growth process of thin film on a given substrate and an aggregate in a vacuum condition are shown. Some characteristic distributions of the obtained structure have been carried out to evaluate the proposed adequate model and to reflect the high complexity of thin films growth process. (paper)
Forest, Loïc; Demongeot, Jacques; Demongeota, Jacques
2006-05-01
The radial growth of conifer trees proceeds from the dynamics of a merismatic tissue called vascular cambium or cambium. Cambium is a thin layer of active proliferating cells. The purpose of this paper was to model the main characteristics of cambial activity and its consecutive radial growth. Cell growth is under the control of the auxin hormone indole-3-acetic. The model is composed of a discrete part, which accounts for cellular proliferation, and a continuous part involving the transport of auxin. Cambium is modeled in a two-dimensional cross-section by a cellular automaton that describes the set of all its constitutive cells. Proliferation is defined as growth and division of cambial cells under neighbouring constraints, which can eliminate some cells from the cambium. The cell-growth rate is determined from auxin concentration, calculated with the continuous model. We studied the integration of each elementary cambial cell activity into the global coherent movement of macroscopic morphogenesis. Cases of normal and abnormal growth of Pinus radiata (D. Don) are modelled. Abnormal growth includes deformed trees where gravity influences auxin transport, producing heterogeneous radial growth. Cross-sectional microscopic views are also provided to validate the model's hypothesis and results.
A laboratory-calibrated model of coho salmon growth with utility for ecological analyses
Manhard, Christopher V.; Som, Nicholas A.; Perry, Russell W.; Plumb, John M.
2018-01-01
We conducted a meta-analysis of laboratory- and hatchery-based growth data to estimate broadly applicable parameters of mass- and temperature-dependent growth of juvenile coho salmon (Oncorhynchus kisutch). Following studies of other salmonid species, we incorporated the Ratkowsky growth model into an allometric model and fit this model to growth observations from eight studies spanning ten different populations. To account for changes in growth patterns with food availability, we reparameterized the Ratkowsky model to scale several of its parameters relative to ration. The resulting model was robust across a wide range of ration allocations and experimental conditions, accounting for 99% of the variation in final body mass. We fit this model to growth data from coho salmon inhabiting tributaries and constructed ponds in the Klamath Basin by estimating habitat-specific indices of food availability. The model produced evidence that constructed ponds provided higher food availability than natural tributaries. Because of their simplicity (only mass and temperature are required as inputs) and robustness, ration-varying Ratkowsky models have utility as an ecological tool for capturing growth in freshwater fish populations.
A Three-period Samuelson-Diamond Growth Model
DEFF Research Database (Denmark)
Blomgren-Hansen, Niels
2005-01-01
Samuelson (1958) analyses a three-period model, whereas Diamod (1965) considers a two-period model. This difference poses the question whether the insights derived by analysing the simple two-period model carry over in the more complicated three-period case. They do. The Samuelson model (no produ...
Mathematical model for predicting molecular-beam epitaxy growth rates for wafer production
International Nuclear Information System (INIS)
Shi, B.Q.
2003-01-01
An analytical mathematical model for predicting molecular-beam epitaxy (MBE) growth rates is reported. The mathematical model solves the mass-conservation equation for liquid sources in conical crucibles and predicts the growth rate by taking into account the effect of growth source depletion on the growth rate. Assumptions made for deducing the analytical model are discussed. The model derived contains only one unknown parameter, the value of which can be determined by using data readily available to MBE growers. Procedures are outlined for implementing the model in MBE production of III-V compound semiconductor device wafers. Results from use of the model to obtain targeted layer compositions and thickness of InP-based heterojunction bipolar transistor wafers are presented
Modelling Eutectic Growth in Unmodified and Modified Near-Eutectic Al-Si Alloy
DEFF Research Database (Denmark)
Tiedje, Niels Skat; Hattel, Jesper Henri; Taylor, John A.
2013-01-01
growth parameters from the literature that depend on the type of modification (unmodified, Na-modified or Sr-modified) are used to describe differences in growth of the alloys. Modelling results are compared with solidification experiments where an Al-12.5wt%Si alloy was cast in unmodified, Na modified......A numerical model that describes solidification of primary aluminium grains and nucleation and growth of eutectic cells is used to analyse the solidification of an Al-12.5wt% Si alloy. Nucleation of eutectic cells is modelled using an Oldfield-type nucleation model where the number of nuclei...... and Sr modified forms. The model confirms experimental observations of how modification and alloy composition influence nucleation, growth and finally the size of eutectic cells in the alloys. Modelling results are used to explain how cooling conditions in the casting act together with the nuclei density...
International Nuclear Information System (INIS)
Kim, Man Cheol; Jang, Seung Cheol; Ha, Jae Joo
2007-01-01
It is generally known that software reliability growth models such as the Jelinski-Moranda model and the Goel-Okumoto's Non-Homogeneous Poisson Process (NHPP) model cannot be applied to safety-critical software due to a lack of software failure data. In this paper, by applying two of the most widely known software reliability growth models to sample software failure data, we demonstrate the possibility of using the software reliability growth models to prove the high reliability of safety-critical software. The high sensitivity of a piece of software's reliability to software failure data, as well as a lack of sufficient software failure data, is also identified as a possible limitation when applying the software reliability growth models to safety-critical software
Creative Destruction and Optimal Patent Life in a Variety-Expanding Growth Model
Lin, Hwan C.
2013-01-01
This paper presents more channels through which the optimal patent life is determined in a R&D-based endogenous growth model that permits growth of new varieties of consumer goods over time. Its modeling features include an endogenous hazard rate facing incumbent monopolists, the prevalence of research congestion, and the aggregate welfare importance of product differentiation. As a result, a patent’s effective life is endogenized and less than its legal life. The model is calibrated to a glo...
A demographic model to predict future growth of the Addo elephant population
A.M. Woodd
1999-01-01
An age-structured demographic model of the growth of the Addo elephant population was developed using parameters calculated from long-term data on the population. The model was used to provide estimates of future population growth. Expansion of the Addo Elephant National Park is currently underway, and the proposed target population size for elephant within the enlarged park is 2700. The model predicts that this population size will be reached during the year 2043, so that the Addo elephant p...
Directory of Open Access Journals (Sweden)
Arjan P Palstra
Full Text Available BACKGROUND: Zebrafish has been largely accepted as a vertebrate multidisciplinary model but its usefulness as a model for exercise physiology has been hampered by the scarce knowledge on its swimming economy, optimal swimming speeds and cost of transport. Therefore, we have performed individual and group-wise swimming experiments to quantify swimming economy and to demonstrate the exercise effects on growth in adult zebrafish. METHODOLOGY/PRINCIPAL FINDINGS: Individual zebrafish (n = 10 were able to swim at a critical swimming speed (U(crit of 0.548±0.007 m s(-1 or 18.0 standard body lengths (BL s(-1. The optimal swimming speed (U(opt at which energetic efficiency is highest was 0.396±0.019 m s(-1 (13.0 BL s(-1 corresponding to 72.26±0.29% of U(crit. The cost of transport at optimal swimming speed (COT(opt was 25.23±4.03 µmol g(-1 m(-1. A group-wise experiment was conducted with zebrafish (n = 83 swimming at U(opt for 6 h day(-1 for 5 days week(-1 for 4 weeks vs. zebrafish (n = 84 that rested during this period. Swimming zebrafish increased their total body length by 5.6% and body weight by 41.1% as compared to resting fish. For the first time, a highly significant exercise-induced growth is demonstrated in adult zebrafish. Expression analysis of a set of muscle growth marker genes revealed clear regulatory roles in relation to swimming-enhanced growth for genes such as growth hormone receptor b (ghrb, insulin-like growth factor 1 receptor a (igf1ra, troponin C (stnnc, slow myosin heavy chain 1 (smyhc1, troponin I2 (tnni2, myosin heavy polypeptide 2 (myhz2 and myostatin (mstnb. CONCLUSIONS/SIGNIFICANCE: From the results of our study we can conclude that zebrafish can be used as an exercise model for enhanced growth, with implications in basic, biomedical and applied sciences, such as aquaculture.
Constitutive modeling of stress-driven grain growth in nanocrystalline metals
Gürses, Ercan
2013-02-08
In this work, we present a variational multiscale model for grain growth in face-centered cubic nanocrystalline (nc) metals. In particular, grain-growth-induced stress softening and the resulting relaxation phenomena are addressed. The behavior of the polycrystal is described by a conventional Taylor-type averaging scheme in which the grains are treated as two-phase composites consisting of a grain interior phase and a grain boundary-affected zone. Furthermore, a grain-growth law that captures the experimentally observed characteristics of the grain coarsening phenomena is proposed. To this end, the grain size is not taken as constant and varies according to the proposed stress-driven growth law. Several parametric studies are conducted to emphasize the influence of the grain-growth rule on the overall macroscopic response. Finally, the model is shown to provide a good description of the experimentally observed grain-growth-induced relaxation in nc-copper. © 2013 IOP Publishing Ltd.
Crabbe, M James C
2007-08-01
Data on colony growth of the branching coral Acropora palmata from fringing reefs off Discovery Bay on the north coast of Jamaica have been obtained over the period 2002-2007 using underwater photography and image analysis by both SCUBA and remotely using an ROV incorporating twin lasers. Growth modelling shows that while logarithmic growth is an approximate model for growth, a 3:3 rational polynomial function provides a significantly better fit to growth data for this coral species. Over the period 2002-2007, involving several cycles of sea surface temperature (SST) change, the rate of growth of A. palmata was largely proportional to rate of change of SST, with R(2)=0.935. These results have implications for the influence of global warming and climate change on coral reef ecosystems.
On the influence of the environment on modeling the fatigue crack growth process
International Nuclear Information System (INIS)
Mc Evily, A.J.
1987-01-01
The effect of the environment at room and elevated temperature were considered with respect to the influence exerted on the basic mechanical aspects of the fatigue crack growth process. An experimental assessment of this influence was obtained by conducting fatigue crack growth tests both in air and vacuum and the results of such experiments are given. Topics considered include crack closure, short crack growth in notched and unnotched specimens, Mode II crack growth, and the effects of oxidation at elevated temperatures. It is shown that the basic mechanisms of fatigue crack growth can be greatly altered by the presence of oxide films at the fatigue crack tip. Modeling the mechanical aspects of the crack growth process is by itself a challenging task. In addition, the environmental considerations adds to the complexity of the modeling process. (Author)
Kristensen, Erika; Hallgrímsson, Benedikt; Morck, Douglas W.; Boyd, Steven K.
2012-01-01
Growth hormone (GH) deficiency is related to an increased fracture risk although it is not clear if this is due to compromised bone quality or a small bone size. We investigated the relationship between bone macrostructure, microarchitecture and mechanical properties in a GH-deficient (GHD) mouse model undergoing GH treatment commencing at an early (prepubertal) or late (postpubertal) time point. Microcomputed tomography images of the femur and L4 vertebra were obtained to quantify macrostruc...
A model of optimal protein allocation during phototrophic growth
Czech Academy of Sciences Publication Activity Database
Faizi, M.; Zavřel, Tomáš; Loureiro, C.; Červený, Jan; Steuer, Ralf
2018-01-01
Roč. 166, apr (2018), s. 26-36 ISSN 0303-2647 R&D Projects: GA MŠk(CZ) LO1415; GA ČR(CZ) GA15-17367S; GA MŠk(CZ) LM2015055 Institutional support: RVO:86652079 Keywords : Cellular protein economy * Cyanobacteria * Microbial growth laws * Photosynthesis * Resource allocation * Systems biology Subject RIV: EI - Biotechnology ; Bionics OBOR OECD: Environmental biotechnology Impact factor: 1.652, year: 2016
Contrasting models of the effect of inflation on growth
Czech Academy of Sciences Publication Activity Database
Gillman, M.; Kejak, Michal
2005-01-01
Roč. 19, č. 1 (2005), s. 113-136 ISSN 0950-0804 R&D Projects: GA ČR GA402/05/2172 Institutional research plan: CEZ:AV0Z70850503 Keywords : balanced- growth -path * cash-in-advance * human capital Subject RIV: AH - Economics Impact factor: 0.911, year: 2005 http://dx.doi.org/10.1111/j.0950-0804.2005.00241.x
Stochastic modeling of cell growth with symmetric or asymmetric division
Marantan, Andrew; Amir, Ariel
2016-07-01
We consider a class of biologically motivated stochastic processes in which a unicellular organism divides its resources (volume or damaged proteins, in particular) symmetrically or asymmetrically between its progeny. Assuming the final amount of the resource is controlled by a growth policy and subject to additive and multiplicative noise, we derive the recursive integral equation describing the evolution of the resource distribution over subsequent generations and use it to study the properties of stable resource distributions. We find conditions under which a unique stable resource distribution exists and calculate its moments for the class of affine linear growth policies. Moreover, we apply an asymptotic analysis to elucidate the conditions under which the stable distribution (when it exists) has a power-law tail. Finally, we use the results of this asymptotic analysis along with the moment equations to draw a stability phase diagram for the system that reveals the counterintuitive result that asymmetry serves to increase stability while at the same time widening the stable distribution. We also briefly discuss how cells can divide damaged proteins asymmetrically between their progeny as a form of damage control. In the appendixes, motivated by the asymmetric division of cell volume in Saccharomyces cerevisiae, we extend our results to the case wherein mother and daughter cells follow different growth policies.
Growth modeling of Cryptomeria japonica by partial trunk analysis
Directory of Open Access Journals (Sweden)
Vinícius Morais Coutinho
2017-06-01
Full Text Available This study aimed to evaluate the growth pattern of Cryptomeria japonica increment (L. F. D. Don. and to describe the probability distribution in stands stablished at the municipality of Rio Negro, Paraná State. Twenty trees were sampled in a 34 years-old stand, with 3 m x 2 m spacing. Wood disks were taken from each tree at 1.3 m above the ground (DBH to perform partial stem analysis. Diameter growth series without bark were used to generate the average cumulative growth curves for DBH (cm, mean annual increment (MAI and current annual increment (CAI. From the increment data, the frequency distribution was evaluated by means of probability density functions (pdfs. The mean annual increment for DBH was 0.78 cm year-1 and the age of intersection of CAI and MAI curves was between the 7th and 8th years. It was found that near 43% of the species increments are concentrated bellow 0.5 cm. The results are useful to define appropriate management strategies for the species for sites similar to the studying regions, defining for example ages of silvicultural intervention, such as thinning.
Dynamic predictive model for growth of Salmonella spp. in scrambled egg mix.
Li, Lin; Cepeda, Jihan; Subbiah, Jeyamkondan; Froning, Glenn; Juneja, Vijay K; Thippareddi, Harshavardhan
2017-06-01
Liquid egg products can be contaminated with Salmonella spp. during processing. A dynamic model for the growth of Salmonella spp. in scrambled egg mix - high solids (SEM) was developed and validated. SEM was prepared and inoculated with ca. 2 log CFU/mL of a five serovar Salmonella spp. cocktail. Salmonella spp. growth data at isothermal temperatures (10, 15, 20, 25, 30, 35, 37, 39, 41, 43, 45, and 47 °C) in SEM were collected. Baranyi model was used (primary model) to fit growth data and the maximum growth rate and lag phase duration for each temperature were determined. A secondary model was developed with maximum growth rate as a function of temperature. The model performance measures, root mean squared error (RMSE, 0.09) and pseudo-R 2 (1.00) indicated good fit for both primary and secondary models. A dynamic model was developed by integrating the primary and secondary models and validated using two sinusoidal temperature profiles, 5-15 °C (low temperature) for 480 h and 10-40 °C (high temperature) for 48 h. The RMSE values for the sinusoidal low and high temperature profiles were 0.47 and 0.42 log CFU/mL, respectively. The model can be used to predict Salmonella spp. growth in case of temperature abuse during liquid egg processing. Copyright Â© 2016. Published by Elsevier Ltd.
Model for predicting non-linear crack growth considering load sequence effects (LOSEQ)
International Nuclear Information System (INIS)
Fuehring, H.
1982-01-01
A new analytical model for predicting non-linear crack growth is presented which takes into account the retardation as well as the acceleration effects due to irregular loading. It considers not only the maximum peak of a load sequence to effect crack growth but also all other loads of the history according to a generalised memory criterion. Comparisons between crack growth predicted by using the LOSEQ-programme and experimentally observed data are presented. (orig.) [de
A generalized-growth model to characterize the early ascending phase of infectious disease outbreaks
Directory of Open Access Journals (Sweden)
Cécile Viboud
2016-06-01
Conclusions: Our findings reveal significant variation in epidemic growth patterns across different infectious disease outbreaks and highlights that sub-exponential growth is a common phenomenon, especially for pathogens that are not airborne. Sub-exponential growth profiles may result from heterogeneity in contact structures or risk groups, reactive behavior changes, or the early onset of interventions strategies, and consideration of “deceleration parameters” may be useful to refine existing mathematical transmission models and improve disease forecasts.
Auconi, Pietro; Scazzocchio, Marco; Defraia, Efisio; McNamara, James A; Franchi, Lorenzo
2014-04-01
To develop a mathematical model that adequately represented the pattern of craniofacial growth in class III subject consistently, with the goal of using this information to make growth predictions that could be amenable to longitudinal verification and clinical use. A combination of computational techniques (i.e. Fuzzy clustering and Network analysis) was applied to cephalometric data derived from 429 untreated growing female patients with class III malocclusion to visualize craniofacial growth dynamics and correlations. Four age groups of subjects were examined individually: from 7 to 9 years of age, from 10 to 12 years, from 13 to 14 years, and from 15 to 17 years. The connections between pathway components of class III craniofacial growth can be visualized from Network profiles. Fuzzy clustering analysis was able to define further growth patterns and coherences of the traditionally reported dentoskeletal characteristics of this structural imbalance. Craniofacial growth can be visualized as a biological, space-constraint-based optimization process; the prediction of individual growth trajectories depends on the rate of membership to a specific 'winner' cluster, i.e. on a specific individual growth strategy. The reliability of the information thus gained was tested to forecast craniofacial growth of 28 untreated female class III subjects followed longitudinally. The combination of Fuzzy clustering and Network algorithms allowed the development of principles for combining multiple auxological cephalometric features into a joint global model and to predict the individual risk of the facial pattern imbalance during growth.
Validation of mathematical model for CZ process using small-scale laboratory crystal growth furnace
Bergfelds, Kristaps; Sabanskis, Andrejs; Virbulis, Janis
2018-05-01
The present material is focused on the modelling of small-scale laboratory NaCl-RbCl crystal growth furnace. First steps towards fully transient simulations are taken in the form of stationary simulations that deal with the optimization of material properties to match the model to experimental conditions. For this purpose, simulation software primarily used for the modelling of industrial-scale silicon crystal growth process was successfully applied. Finally, transient simulations of the crystal growth are presented, giving a sufficient agreement to experimental results.
A generalized preferential attachment model for business firms growth rates. I. Empirical evidence
Pammolli, F.; Fu, D.; Buldyrev, S. V.; Riccaboni, M.; Matia, K.; Yamasaki, K.; Stanley, H. E.
2007-05-01
We introduce a model of proportional growth to explain the distribution P(g) of business firm growth rates. The model predicts that P(g) is Laplace in the central part and depicts an asymptotic power-law behavior in the tails with an exponent ζ = 3. Because of data limitations, previous studies in this field have been focusing exclusively on the Laplace shape of the body of the distribution. We test the model at different levels of aggregation in the economy, from products, to firms, to countries, and we find that the predictions are in good agreement with empirical evidence on both growth distributions and size-variance relationships.
Auditing predictive models : a case study in crop growth
Metselaar, K.
1999-01-01
Methods were developed to assess and quantify the predictive quality of simulation models, with the intent to contribute to evaluation of model studies by non-scientists. In a case study, two models of different complexity, LINTUL and SUCROS87, were used to predict yield of forage maize
Energy Technology Data Exchange (ETDEWEB)
Denysenko, I; Azarenkov, N A, E-mail: idenysenko@yahoo.com [School of Physics and Technology, V N Karazin Kharkiv National University, 4 Svobody sq., 61077 Kharkiv (Ukraine)
2011-05-04
Results on modelling of the plasma-assisted growth of vertically aligned carbon nanostructures and of the energy exchange between the plasma and the growing nanostructures are reviewed. Growth of carbon nanofibres and single-walled carbon nanotubes is considered. Focus is made on studies that use the models based on mass balance equations for species, which are adsorbed on catalyst nanoparticles or walls of the nanostructures. It is shown that the models can be effectively used for the study and optimization of nanostructure growth in plasma-enhanced chemical vapour deposition. The results from these models are in good agreement with the available experimental data on the growth of nanostructures. It is discussed how input parameters for the models may be obtained.
Modification of the FRI crack growth model formulation from a mathematical viewpoint
International Nuclear Information System (INIS)
Hashimoto, Tsuneyuki; Koshiishi, Masato
2009-01-01
The FRI model of crack growth, which incorporates mechanical properties into the slip oxidation mechanism of crack advance, is an extension of the well-known Ford-Andresen model. When the exponent of the oxidation current decay curve is set close to 1, however, the FRI model gives an infinite crack growth rate. Here, the oxidation decay curve integral is revised to eliminate this divergence, and modified crack growth rate equations are derived. Also presented here is a procedure for determining the oxidation current parameters from the curve-fitting to measurements of crack growth rate. Parameter value determination and crack growth calculations are illustrated for cold-worked Type 316L stainless steel. (author)
Computational modeling of the mechanical modulation of the growth plate by sustained loading
Directory of Open Access Journals (Sweden)
Narváez-Tovar Carlos A
2012-09-01
Full Text Available Abstract This paper presents a computational model that describes the growth of the bone as a function of the proliferation and hypertrophy of chondrocytes in the growth plate. We have included the effects of the mechanical loads on the sizes of the proliferative and hypertrophic areas, the number of proliferative chondrocytes and the final size of the hypertrophic chondrocytes. The validation of the model was performed with experimental data published on other investigations about proximal tibia of rats, subjected to sustained axial stresses of 0.1 MPa, 0.0 MPa, -0.1 MPa and −0.2 MPa. Growth was simulated during 23 days, obtaining numerical errors between 2.77% and 3.73% with respect to experimental growth rates. The results obtained show that the model adequately simulates the behavior of the growth plate and the effect of mechanical loads over its cellular activity.
Automatic Assessment of Craniofacial Growth in a Mouse Model of Crouzon Syndrome
DEFF Research Database (Denmark)
Thorup, Signe Strann; Larsen, Rasmus; Darvann, Tron Andre
2009-01-01
for each mouse-type; growth models were created using linear interpolation and visualized as 3D animations. Spatial regions of significantly different growth were identified using the local False Discovery Rate method, estimating the expected percentage of false predictions in a set of predictions. For all......-rigid volumetric image registration was applied to micro-CT scans of ten 4-week and twenty 6-week euthanized mice for growth modeling. Each age group consisted of 50% normal and 50% Crouzon mice. Four 3D mean shapes, one for each mouse-type and age group were created. Extracting a dense field of growth vectors...... a tool for spatially detailed automatic phenotyping. MAIN OBJECTIVES OF PRESENTATION: We will present a 3D growth model of normal and Crouzon mice, and differences will be statistically and visually compared....
Growth and energy nexus in Europe revisited: Evidence from a fixed effects political economy model
International Nuclear Information System (INIS)
Menegaki, Angeliki N.; Ozturk, Ilhan
2013-01-01
This is an empirical study on the causal relationship between economic growth and energy for 26 European countries in a multivariate panel framework over the period 1975–2009 using a two-way fixed effects model and including greenhouse gas emissions, capital, fossil energy consumption, Herfindahl index (political competition) and number of years the government chief executive stays in office (political stability) as independent variables in the model. Empirical results confirm bidirectional causality between growth and political stability, capital and political stability, capital and fossil energy consumption. Whether political stability favors the implementation of growth or leads to corruption demands further research. - Highlights: • Economic growth and energy for 26 European countries is examined. • Two-way fixed effects model with political economy variables is employed. • Bidirectional causality is observed between growth and political stability
The synergy of modeling and novel experiments for melt crystal growth research
Derby, Jeffrey J.
2018-05-01
Computational modeling and novel experiments, when performed together, can enable the identification of new, fundamental mechanisms important for the growth of bulk crystals from the melt. In this paper, we present a compelling example of this synergy via the discovery of previously unascertained physical mechanisms that govern the engulfment of silicon carbide particles during the growth of crystalline silicon.
Calibration and validation of the crop growth model daisy for spring barley in the Czech Republic
Czech Academy of Sciences Publication Activity Database
Pohanková, Eva; Hlavinka, Petr; Takáč, J.; Žalud, Zdeněk; Trnka, Miroslav
2015-01-01
Roč. 63, č. 4 (2015), s. 1177-1186 ISSN 1211-8516 R&D Projects: GA MŠk(CZ) LD13030; GA MŠk(CZ) LO1415 Institutional support: RVO:67179843 Keywords : Tolar * Crop growth model * daisy * Field experiments * Growth dynamics * Phenology * Spring barley Subject RIV: EH - Ecology, Behaviour
Proces-based modeling of the overflow induced growth of erosional channels
Tuan, T.Q.; Stive, M.J.F.; Verhagen, H.J.; Visser, P.J.
2008-01-01
A new process-based approach is introduced for a more efficient computation of the overflow-induced growth of an erosional channel in a noncohesive homogeneous narrow landmass such as the breach growth in a sand-dike. The approach is easy to incorporate in a 1D/2DV morphodynamic model to compute the
Levi, M. [=Marcel M.; Biemond, B. J.; Sturk, A.; Hoek, J.; ten Cate, J. W.
1991-01-01
We studied the effect of an ionic high osmolar contrast medium (Ioxitalamate), an ionic low osmolar contrast medium (Ioxaglate) and various nonionic low osmolar contrast media (Iopamidol, Iopromide and Iohexol) on thrombus growth in a rabbit jugular vein thrombosis model. Thrombus growth was
Development and validation of SUCROS-Cotton : A potential crop growth simulation model for cotton
Zhang, L.; Werf, van der W.; Cao, W.; Li, B.; Pan, X.; Spiertz, J.H.J.
2008-01-01
A model for the development, growth and potential production of cotton (SUCROS-Cotton) was developed. Particular attention was given to the phenological development of the plant and the plasticity of fruit growth in response to temperature, radiation, daylength, variety traits, and management. The
Constitutive modeling of stress-driven grain growth in nanocrystalline metals
Gü rses, Ercan; Wafai, Husam; El Sayed, Tamer S.
2013-01-01
the influence of the grain-growth rule on the overall macroscopic response. Finally, the model is shown to provide a good description of the experimentally observed grain-growth-induced relaxation in nc-copper. © 2013 IOP Publishing Ltd.
To Save or to Consume: Linking Growth Theory with the Keynesian Model
Kwok, Yun-kwong
2007-01-01
In the neoclassical growth theory, higher saving rate gives rise to higher output per capita. However, in the Keynesian model, higher saving rate causes lower consumption, which may lead to a recession. Students may ask, "Should we save or should we consume?" In most of the macroeconomics textbooks, economic growth and Keynesian economics are in…
A model for arterial adaptation combining microstructural collagen remodeling and 3D tissue growth
Machyshyn, I.; Bovendeerd, P.H.M.; Ven, van de A.A.F.; Rongen, P.M.J.; Vosse, van de F.N.
2010-01-01
Long-term adaptation of soft tissues is realized through growth and remodeling (G&R). Mathematical models are powerful tools in testing hypotheses on G&R and supporting the design and interpretation of experiments. Most theoretical G&R studies concentrate on description of either growth or
Predicting growth of the healthy infant using a genome scale metabolic model
DEFF Research Database (Denmark)
Nilsson, Avlant; Mardinoglu, Adil; Nielsen, Jens
2017-01-01
to simulate the mechanisms of growth and integrate data about breast-milk intake and composition with the infant's biomass and energy expenditure of major organs. The model predicted daily metabolic fluxes from birth to age 6 months, and accurately reproduced standard growth curves and changes in body...
Firm dynamic analysis for urban land use and economic growth modelling
Che'Man, N.; Sabri, S.; Hosni, N.; Timmermans, H.J.P.
2013-01-01
In urban growth processes, urbanisation is highly influenced by economic growth which triggers the dynamics of economic agents and land uses. This is consisted of complex subsystems which need sophisticated methods like agent-based modelling and simulation to understand the pattern, behaviour and
Innovation, Decentralization and Planning in a Multi-Region Model of Schumpeterian Economic Growth
Batabyal, A.; Nijkamp, P.
2014-01-01
We study innovation and the resulting Schumpeterian economic growth that this innovation gives rise to in a model with N heterogeneous regions. For each region i where i = 1,…,N, our analysis leads to six findings. First, we define the balanced growth path (BGP) allocations and the equilibrium of
A Systematic Approach for Identifying Level-1 Error Covariance Structures in Latent Growth Modeling
Ding, Cherng G.; Jane, Ten-Der; Wu, Chiu-Hui; Lin, Hang-Rung; Shen, Chih-Kang
2017-01-01
It has been pointed out in the literature that misspecification of the level-1 error covariance structure in latent growth modeling (LGM) has detrimental impacts on the inferences about growth parameters. Since correct covariance structure is difficult to specify by theory, the identification needs to rely on a specification search, which,…
Model of metastatic growth valuable for radionuclide therapy
International Nuclear Information System (INIS)
Bernhardt, Peter; Ahlman, Haakan; Forssell-Aronsson, Eva
2003-01-01
The aim was to make a Monte Carlo simulation approach to estimate the distribution of tumor sizes and to study the curative potential of three candidate radionuclides for radionuclide therapy: the high-energy electron emitter 90 Y, the medium-energy electron emitter 177 Lu and the low-energy electron emitter 103m Rh. A patient with hepatocellular carcinoma with recently published serial CT data on tumor growth in the liver was used. From these data the growth of the primary tumor, and the metastatis formation rate, were estimated. Assuming the same tumor growth of the primary and all metastases and the same metastatis formation rate from both primary and metastases the metastatic size distribution was simulated for various time points. Tumor cure of the metastatic size distribution was simulated for uniform activity distribution of three radionuclides; the high-energy electron emitter 90 Y, the mean-energy electron emitter 177 Lu and the low-energy electron emitter 103m Rh. The simulation of a tumor cure was performed for various time points and tumor-to-normal tissue activity concentrations, TNC. It was demonstrated that it is important to start therapy as early as possible after diagnosis. It was of crucial importance to use an optimal radionuclide for therapy. These simulations demonstrated that 90 Y was not suitable for systemic radionuclide therapy, due to the low absorbed fraction of the emitted electrons in small tumors ( 103m Rh was slightly better than 177 Lu. For high TNC values low-energy electron emitters, e.g., 103m Rh was the best choice for tumor cure. However, the short half-life of 103m Rh (56 min) might not be optimal for therapy. Therefore, other low-energy electron emitters, or alpha emitters, should be considered for systemic targeted therapy
Modified inorganic surfaces as a model for hydroxyapatite growth
Pramatarova, Lilyana
2006-01-01
The process by which organisms in Nature create minerals is known as biomineralization - a process that involves complex interactions between inorganic ions, crystals and organic molecules; resulting in a controlled nucleation and growth of minerals from aqueous solutions. During the last few decades, biomineralization has been intensively studied, due to its involvement in a wide range of biological events; starting with the formation of bones, teeth, cartilage, shells, coral (so-called physiological mineralization) and encompassing pathological mineralization, i.e. the formation of kidney st
Model of emittance growth in a self-pinched beam
International Nuclear Information System (INIS)
Lee, E.P.; Yu, S.S.
1979-01-01
A semi-phenomenological formula is proposed for the change of emittance of a self-pinched beam which is not matched to its equilibrium radius. Near equilibrium this formula, coupled with an envelope equation, yields the damped sausage oscillations observed in simulation and experiments. For a beam which is injected cold (no transverse velocity spread), the formula coincides with the analytically calculated initial growth of emittance. The basic theory is developed here and used to compute the linear damping rate for several current profiles. The resultant non-linear increase in equilibrium quantities is also calculated in lowest order of the degree of mismatch
Evaluating Non-Linear Regression Models in Analysis of Persian Walnut Fruit Growth
Directory of Open Access Journals (Sweden)
I. Karamatlou
2016-02-01
Full Text Available Introduction: Persian walnut (Juglans regia L. is a large, wind-pollinated, monoecious, dichogamous, long lived, perennial tree cultivated for its high quality wood and nuts throughout the temperate regions of the world. Growth model methodology has been widely used in the modeling of plant growth. Mathematical models are important tools to study the plant growth and agricultural systems. These models can be applied for decision-making anddesigning management procedures in horticulture. Through growth analysis, planning for planting systems, fertilization, pruning operations, harvest time as well as obtaining economical yield can be more accessible.Non-linear models are more difficult to specify and estimate than linear models. This research was aimed to studynon-linear regression models based on data obtained from fruit weight, length and width. Selecting the best models which explain that fruit inherent growth pattern of Persian walnut was a further goal of this study. Materials and Methods: The experimental material comprising 14 Persian walnut genotypes propagated by seed collected from a walnut orchard in Golestan province, Minoudasht region, Iran, at latitude 37◦04’N; longitude 55◦32’E; altitude 1060 m, in a silt loam soil type. These genotypes were selected as a representative sampling of the many walnut genotypes available throughout the Northeastern Iran. The age range of walnut trees was 30 to 50 years. The annual mean temperature at the location is16.3◦C, with annual mean rainfall of 690 mm.The data used here is the average of walnut fresh fruit and measured withgram/millimeter/day in2011.According to the data distribution pattern, several equations have been proposed to describesigmoidal growth patterns. Here, we used double-sigmoid and logistic–monomolecular models to evaluate fruit growth based on fruit weight and4different regression models in cluding Richards, Gompertz, Logistic and Exponential growth for evaluation
Dynamic Predictive Model for Growth of Bacillus cereus from Spores in Cooked Beans.
Juneja, Vijay K; Mishra, Abhinav; Pradhan, Abani K
2018-02-01
Kinetic growth data for Bacillus cereus grown from spores were collected in cooked beans under several isothermal conditions (10 to 49°C). Samples were inoculated with approximately 2 log CFU/g heat-shocked (80°C for 10 min) spores and stored at isothermal temperatures. B. cereus populations were determined at appropriate intervals by plating on mannitol-egg yolk-polymyxin agar and incubating at 30°C for 24 h. Data were fitted into Baranyi, Huang, modified Gompertz, and three-phase linear primary growth models. All four models were fitted to the experimental growth data collected at 13 to 46°C. Performances of these models were evaluated based on accuracy and bias factors, the coefficient of determination ( R 2 ), and the root mean square error. Based on these criteria, the Baranyi model best described the growth data, followed by the Huang, modified Gompertz, and three-phase linear models. The maximum growth rates of each primary model were fitted as a function of temperature using the modified Ratkowsky model. The high R 2 values (0.95 to 0.98) indicate that the modified Ratkowsky model can be used to describe the effect of temperature on the growth rates for all four primary models. The acceptable prediction zone (APZ) approach also was used for validation of the model with observed data collected during single and two-step dynamic cooling temperature protocols. When the predictions using the Baranyi model were compared with the observed data using the APZ analysis, all 24 observations for the exponential single rate cooling were within the APZ, which was set between -0.5 and 1 log CFU/g; 26 of 28 predictions for the two-step cooling profiles also were within the APZ limits. The developed dynamic model can be used to predict potential B. cereus growth from spores in beans under various temperature conditions or during extended chilling of cooked beans.
Modeling and simulation of axisymmetric coating growth on nanofibers
International Nuclear Information System (INIS)
Moore, K.; Clemons, C. B.; Kreider, K. L.; Young, G. W.
2007-01-01
This work is a modeling and simulation extension of an integrated experimental/modeling investigation of a procedure to coat nanofibers and core-clad nanostructures with thin film materials using plasma enhanced physical vapor deposition. In the experimental effort, electrospun polymer nanofibers are coated with metallic materials under different operating conditions to observe changes in the coating morphology. The modeling effort focuses on linking simple models at the reactor level, nanofiber level, and atomic level to form a comprehensive model. The comprehensive model leads to the definition of an evolution equation for the coating free surface. This equation was previously derived and solved under a single-valued assumption in a polar geometry to determine the coating morphology as a function of operating conditions. The present work considers the axisymmetric geometry and solves the evolution equation without the single-valued assumption and under less restrictive assumptions on the concentration field than the previous work
Simulation modeling on the growth of firm's safety management capability
Institute of Scientific and Technical Information of China (English)
LIU Tie-zhong; LI Zhi-xiang
2008-01-01
Aiming to the deficiency of safety management measure, established simulation model about firm's safety management capability(FSMC) based on organizational learning theory. The system dynamics(SD) method was used, in which level and rate system, variable equation and system structure flow diagram was concluded. Simulation model was verified from two aspects: first, model's sensitivity to variable was tested from the gross of safety investment and the proportion of safety investment; second, variables dependency was checked up from the correlative variable of FSMC and organizational learning. The feasibility of simulation model is verified though these processes.
Oscillations in a Growth Model with Capital, Technology and Environment with Exogenous Shocks
Directory of Open Access Journals (Sweden)
Wei-Bin Zhang
2015-07-01
Full Text Available This paper generalizes the dynamic growth model with wealth accumulation, technological change and environmental change by Zhang (2012 by making all the parameters as time-dependent parameters. The model treats physical capital accumulation, knowledge creation and utilization, and environmental change as endogenous variables. It synthesizes the basic ideas of the neoclassical growth theory, Arrow’s learning-by-doing model and the traditional dynamic models of environmental change within a comprehensive framework. The behavior of the household is described with an alternative approach to household behavior. We simulated the model to demonstrate existence of equilibrium points, motion of the dynamic system, and oscillations due to different exogenous shocks.
Xylem formation can be modeled statistically as a function of primary growth and cambium activity.
Huang, Jian-Guo; Deslauriers, Annie; Rossi, Sergio
2014-08-01
Primary (budburst, foliage and shoot) growth and secondary (cambium and xylem) growth of plants play a vital role in sequestering atmospheric carbon. However, their potential relationships have never been mathematically quantified and the underlying physiological mechanisms are unclear. We monitored primary and secondary growth in Picea mariana and Abies balsamea on a weekly basis from 2010 to 2013 at four sites over an altitudinal gradient (25-900 m) in the eastern Canadian boreal forest. We determined the timings of onset and termination through the fitted functions and their first derivative. We quantified the potential relationships between primary growth and secondary growth using the mixed-effects model. We found that xylem formation of boreal conifers can be modeled as a function of cambium activity, bud phenology, and shoot and needle growth, as well as species- and site-specific factors. Our model reveals that there may be an optimal mechanism to simultaneously allocate the photosynthetic products and stored nonstructural carbon to growth of different organs at different times in the growing season. This mathematical link can bridge phenological modeling, forest ecosystem productivity and carbon cycle modeling, which will certainly contribute to an improved prediction of ecosystem productivity and carbon equilibrium. © 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.
Sadeghi, Neda; Prastawa, Marcel; Fletcher, P Thomas; Gilmore, John H; Lin, Weili; Gerig, Guido
2012-01-01
A population growth model that represents the growth trajectories of individual subjects is critical to study and understand neurodevelopment. This paper presents a framework for jointly estimating and modeling individual and population growth trajectories, and determining significant regional differences in growth pattern characteristics applied to longitudinal neuroimaging data. We use non-linear mixed effect modeling where temporal change is modeled by the Gompertz function. The Gompertz function uses intuitive parameters related to delay, rate of change, and expected asymptotic value; all descriptive measures which can answer clinical questions related to growth. Our proposed framework combines nonlinear modeling of individual trajectories, population analysis, and testing for regional differences. We apply this framework to the study of early maturation in white matter regions as measured with diffusion tensor imaging (DTI). Regional differences between anatomical regions of interest that are known to mature differently are analyzed and quantified. Experiments with image data from a large ongoing clinical study show that our framework provides descriptive, quantitative information on growth trajectories that can be directly interpreted by clinicians. To our knowledge, this is the first longitudinal analysis of growth functions to explain the trajectory of early brain maturation as it is represented in DTI.
Age structure and capital dilution effects in neo-classical growth models.
Blanchet, D
1988-01-01
Economists often over estimate capital dilution effects when applying neoclassical growth models which use age structured population and depreciation of capital stock. This occurs because capital stock is improperly characterized. A standard model which assumes a constant depreciation of capital intimates that a population growth rate equal to a negative constant savings ratio is preferable to any higher growth rate. Growth rates which are lower than a negative constant savings ratio suggest an ever growing capital/labor ratio and an ever growing standard of living, even if people do not save. This is suggested because the natural reduction of the capital stock through depreciation is slower than the population decrease which is simply unrealistic. This model overlooks the fact that low or negative growth rates result in an ageing of the capital stock, and this ageing subsequently results in an increase of the overall rate of capital depreciation. In that overly simplistic model, depreciation was assumed independent of the age of the captial stock. Incorporating depreciation as a variable into a model allows a more symmetric treatment of capital. Using models with heterogenous capital, this article explores what occurs when more than 1 kind of capital good is involved in production and when these various captial goods have different lengths of life. Applying economic models, it also examines what occurs when the length of life of capital may vary. These variations correct the negative impact that population growth can have on per capital production and consumption.
Schröter, M.; Härdtle, W.; Oheimb, von G.
2012-01-01
Competition for canopy space is a process of major importance in forest dynamics. Although virgin and old-growth European beech (Fagus sylvatica L.) forests in Europe have been studied for many years, there are to date no studies of individual-tree crown plasticity and the way this is influenced by
Discrete modelling of ductile crack growth by void growth to coalescence
DEFF Research Database (Denmark)
Tvergaard, Viggo
2007-01-01
of the ligaments between the crack-tip and a void or between voids involves the development of very large strains, which are included in the model by using remeshing at several stages of the plastic deformation. The material is here described by standard isotropic hardening Mises theory. For a very small void...
Assessment of local models and tools for analyzing smart-growth strategies.
2007-07-01
There is a growing interest in California in smart-growth land- use and transportation : strategies designed to provide mobility options and reduce demand on automobile-oriented facilities. This study focuses on models and tools available for u...
Abnormal grain growth: a non-equilibrium thermodynamic model for multi-grain binary systems
Czech Academy of Sciences Publication Activity Database
Svoboda, Jiří; Fischer, F. D.
2014-01-01
Roč. 22, č. 1 (2014), Art . No. 015013 ISSN 0965-0393 Institutional support: RVO:68081723 Keywords : grain boundary segregation * abnormal grain growth * theory * modelling * solute drag Subject RIV: BJ - Thermodynamics Impact factor: 2.167, year: 2014
An Evaluation of Growth Models as Predictive Tools for Estimates at Completion (EAC)
National Research Council Canada - National Science Library
Trahan, Elizabeth N
2009-01-01
...) as the Estimates at Completion (EAC). Our research evaluates the prospect of nonlinear growth modeling as an alternative to the current predictive tools used for calculating EAC, such as the Cost Performance Index (CPI...
Effects of lag and maximum growth in contaminant transport and biodegradation modeling
International Nuclear Information System (INIS)
Wood, B.D.; Dawson, C.N.
1992-06-01
The effects of time lag and maximum microbial growth on biodegradation in contaminant transport are discussed. A mathematical model is formulated that accounts for these effects, and a numerical case study is presented that demonstrates how lag influences biodegradation
Some factors that will affect the next generation of forest growth models
International Nuclear Information System (INIS)
Leary, R.A.
1988-01-01
This paper discusses several types of factors that affect the form and referents of future growth models. These include philosophical, scientific, technological, educational, and organizational factors. Each factor is presented individually
Surface-bounded growth modeling applied to human mandibles
DEFF Research Database (Denmark)
Andresen, Per Rønsholt; Brookstein, F. L.; Conradsen, Knut
2000-01-01
From a set of longitudinal three-dimensional scans of the same anatomical structure, the authors have accurately modeled the temporal shape and size changes using a linear shape model. On a total of 31 computed tomography scans of the mandible from six patients, 14,851 semilandmarks are found...
Initial growth of phytoplankton in turbid estuaries: a simple model
de Swart, H.E.; Schuttelaars, H.; Talke, S.A.
2009-01-01
An idealised model is presented and analysed to gain more fundamental understanding about the dynamics of phytoplankton blooms in well-mixed, suspended sediment dominated estuaries. The model describes the behaviour of subtidal currents, suspended sediments, nutrients and phytoplankton in a channel
Directory of Open Access Journals (Sweden)
Peng Bin
2016-06-01
Full Text Available Given the shrinking proportion of agriculture output and the growing mobility of the labor force in China, how agricultural labor productivity develops has become an increasingly attractive topic for researchers and policy makers. This study aims to depict the development trajectory of agricultural labor productivity in China after its WTO entry. Based on a balanced panel data containing 287 Chinese prefectures from 2000 to 2013, this study applies the Latent Growth Curve Model (LGCM and finds that the agricultural labor productivity follows a piecewise growth path with two breaking points in the years of 2004 and 2009. This may stem from some exogenous stimulus, such as supporting policies launched in the breaking years. Further statistical analysis shows an expanding gap of agricultural labor productivity among different Chinese prefectures.
Structural equation models of VMT growth in US urbanised areas.
Ewing, Reid; Hamidi, Shima; Gallivan, Frank; Nelson, Arthur C.; Grace, James B.
2014-01-01
Vehicle miles travelled (VMT) is a primary performance indicator for land use and transportation, bringing with it both positive and negative externalities. This study updates and refines previous work on VMT in urbanised areas, using recent data, additional metrics and structural equation modelling (SEM). In a cross-sectional model for 2010, population, income and freeway capacity are positively related to VMT, while gasoline prices, development density and transit service levels are negatively related. Findings of the cross-sectional model are generally confirmed in a more tightly controlled longitudinal study of changes in VMT between 2000 and 2010, the first model of its kind. The cross-sectional and longitudinal models together, plus the transportation literature generally, give us a basis for generalising across studies to arrive at elasticity values of VMT with respect to different urban variables.
Industry growth, work role characteristics, and job satisfaction: a cross-level mediation model.
Ford, Michael T; Wooldridge, Jessica D
2012-10-01
The associations between industry revenue growth, individual work role characteristics, and job satisfaction were examined in this cross-level mediation analysis. Work roles were expected to be more autonomous, involve greater skill variety, and offer more opportunities for growth and development for workers in growing industries than for workers in declining industries. Supervisor support was also hypothesized to be stronger for workers in high-growth industries. Results from a nationally representative (U.S.) sample of service industry workers, using multilevel modeling, supported these propositions and suggest that job enrichment mediates relations between industry growth and job satisfaction. Associations between industry growth and autonomy were also stronger among workers in occupations that are less normatively autonomous, suggesting that industry growth fosters a weakening, and industry decline a strengthening, of traditional differences in autonomy across work roles. These results contribute to a multilevel perspective on organizational environments, individual work roles, and worker attitudes and well-being.
"A Simplified 'Benchmark” Stock-flow Consistent (SFC) Post-Keynesian Growth Model"
Claudio H. Dos Santos; Gennaro Zezza
2007-01-01
Despite being arguably one of the most active areas of research in heterodox macroeconomics, the study of the dynamic properties of stock-flow consistent (SFC) growth models of financially sophisticated economies is still in its early stages. This paper attempts to offer a contribution to this line of research by presenting a simplified Post-Keynesian SFC growth model with well-defined dynamic properties, and using it to shed light on the merits and limitations of the current heterodox SFC li...
Trade Liberalisation, Growth and Poverty in Senegal: a Dynamic Microsimulation CGE Model Analysis
Nabil Annabi; Fatou Cissé; John Cockburn; Bernard Decaluwé
2005-01-01
Much current debate focuses on the role of growth in alleviating poverty. However, the majority of computable general equilibrium (CGE) models used in poverty and inequality analysis are static in nature. The inability of this kind of model to account for growth (accumulation) effects makes them inadequate for long run analysis of the poverty and inequality impacts of economic policies. They exclude accumulation effects and do not allow the study of the transition path of the economy where sh...
LEON-GONZALEZ, Roberto; VINAYAGATHASAN, Thanabalasingam
2013-01-01
This paper investigates the determinants of growth in the Asian developing economies. We use Bayesian model averaging (BMA) in the context of a dynamic panel data growth regression to overcome the uncertainty over the choice of control variables. In addition, we use a Bayesian algorithm to analyze a large number of competing models. Among the explanatory variables, we include a non-linear function of inflation that allows for threshold effects. We use an unbalanced panel data set of 27 Asian ...
A search for distinctive features of demand-led growth models
Sergio Parrinello
2014-01-01
This paper aims at a critical and constructive assessment of some extensions of Keynes’s analysis of effective demand to the long period and growth. A criticism is addressed to a single-cause interpretation of the demand-led growth models and to the notion of normal capacity utilization adopted in such models. A positive argument tries to find a distinctive characterization of those extensions in the productive and financial conditions that make effective the autonomous changes in aggregate d...
Modelling the Growth and Volatility in Daily International Mass Tourism to Peru
Jose Angelo Divino; Michael McAleer
2009-01-01
Peru is a South American country that is divided into two parts by the Andes Mountains. The rich historical, cultural and geographic diversity has led to the inclusion of ten Peruvian sites on UNESCO’s World Heritage List. For the potential negative impacts of mass tourism on the environment, and hence on future international tourism demand, to be managed appropriately require modelling growth rates and volatility adequately. The paper models the growth rate and volatility (or the variability...
Fiscal and monetary policy interactions in an endogenous growth model with financial intermediaries
Espinosa, Marco A.; Yip, Chong K.
1995-01-01
We review some inflationary and growth claims surrounding fiscal and monetary policy interactions. While financial intermediation has long been acknowledged as a key mechanism in the transmission of these interactions, only recently have economists incorporated the explicit modeling of such intermediaries in their analyses. Here we model financial intermediaries explicitly. We find that the relation between growth and inflation depends crucially on the agents' degree of relative risk aversion...
Re-parametrization of a swine model to predict growth performance of broilers
Dukhta, G.; van Milgen, Jacob; Kövér, G.; Halas, V.
2017-01-01
The aim of the study was to investigate whether a pig growth model is suitable to be modified and adapted for broilers. As monogastric animals, pigs and poultry share many similarities in their digestion and metabolism, many structures (body protein and lipid stores) and the nutrient flows of the underlying metabolic pathways are similar among species. For that purpose, the InraPorc model was used as a basis to predict growth performance and body composition at slaughter in broilers. First...