Growth Models (growth + models)

Distribution by Scientific Domains

Kinds of Growth Models

  • endogenous growth models


  • Selected Abstracts


    On the Dynamics of Basic Growth Models: Ratio Stability vs.

    GERMAN ECONOMIC REVIEW, Issue 4 2009
    Convergence, Divergence in State Space
    Balanced growth; convergence; divergence; state space dynamics; ratio stability Abstract. We show for a class of basic growth models that convergence in ratios does not imply the pathwise convergence to the corresponding balanced growth path in the state space. We derive conditions on parameters and on the elasticity of the savings function for convergence or divergence and apply our results to the Solow model, an augmented Solow model as well as to an optimal growth model. An implication for the convergence debate is that two economies that differ only in the initial capital stock and converge in per capita terms might diverge to infinity in absolute terms. [source]


    Thickness-Dependent Structural Evolutions and Growth Models in Relation to Carrier Transport Properties in Polycrystalline Pentacene Thin Films,

    ADVANCED FUNCTIONAL MATERIALS, Issue 17 2007
    H.-L. Cheng
    Abstract Thickness-dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin-film phase and then to the triclinic bulk phase as measured by the increased tilt angle (,tilt) of the pentacene molecule from the c- axis toward the a- axis. We propose a growth model that rationalizes the ,tilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C,C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries. [source]


    Sexual orientation and substance use trajectories in emerging adulthood

    ADDICTION, Issue 7 2010
    Amelia E. Talley
    ABSTRACT Aims The current study examined developmental changes in substance use behaviors (SUBS) based upon sexual orientation. The analyses also attempted to address a number of methodological limitations in the extant longitudinal literature (i.e. distinct operationalizations of sexual orientation, timing of sexual orientation assessment with respect to reports of SUBs, non-linear growth). Participants Data were drawn from a longitudinal study of incoming first-time college students at a large public university (n = 3720). Design After a paper-and-pencil assessment just prior to matriculation, participants completed a web-based survey every fall and spring for 4 years (sub-sample n = 2854). Findings Latent growth models revealed that sexual minorities demonstrated significant heterogeneity with regard to substance use trajectories. Initial levels and trajectories of the frequency of substance use for sexual minority individuals were distinct, generally, from their exclusively heterosexual peers. Methodologically, the timing of the assessment of sexual orientation influenced the results, and modeling non-linear components indicated that sexual minorities are at risk for exponential increases in their frequency of certain SUBs over time (i.e. drunkenness; cannabis use). Conclusions Sexual minority and majority individuals exhibited differences in SUBs during emerging adulthood, especially when using self-identification to define sexual orientation. Individuals who endorsed a sexual minority self-identification at the onset of emerging adulthood, as opposed to 4 years later, evidenced exponential increases in rates of drunkenness and cannabis use. These results support that the timing of assessment is important and that some trajectories of sexual minority SUBs are non-linear during this developmental period. [source]


    WHY CHINA INDUSTRIALIZED AFTER ENGLAND

    ECONOMIC INQUIRY, Issue 4 2010
    BARRY S. KAHN
    Although industrialization first occurred in England, it is thought that China, not England, may have been the world leader in technology at the time. Yet, China did not industrialize until 150 yr after England and nearly a century after less advanced European countries. This represents a puzzle because two-sector neoclassical growth models, such as Hansen and Prescott (2002), that accurately match industrialization, require that more technologically advanced countries industrialize at an earlier date. I find that a model that accounts for cross-country heterogeneities in population density accurately predicts the timing of industrialization in China. (JEL F43, N10, N30, O11, O14, O41) [source]


    The Impact of Vertical Scaling Decisions on Growth Interpretations

    EDUCATIONAL MEASUREMENT: ISSUES AND PRACTICE, Issue 4 2009
    Derek C. Briggs
    Most growth models implicitly assume that test scores have been vertically scaled. What may not be widely appreciated are the different choices that must be made when creating a vertical score scale. In this paper empirical patterns of growth in student achievement are compared as a function of different approaches to creating a vertical scale. Longitudinal item-level data from a standardized reading test are analyzed for two cohorts of students between Grades 3 and 6 and Grades 4 and 7 for the entire state of Colorado from 2003 to 2006. Eight different vertical scales were established on the basis of choices made for three key variables: Item Response Theory modeling approach, linking approach, and ability estimation approach. It is shown that interpretations of empirical growth patterns appear to depend upon the extent to which a vertical scale has been effectively "stretched" or "compressed" by the psychometric decisions made to establish it. While all of the vertical scales considered show patterns of decelerating growth across grade levels, there is little evidence of scale shrinkage. [source]


    Opportunism of Conidiobolus obscurus stems from depression of infection in situ to progeny colonies of host alatae as disseminators of the aphid-pathogenic fungus

    ENVIRONMENTAL MICROBIOLOGY, Issue 4 2007
    Guo-Zhong Zhang
    Summary Conidiobolus (Entomophthorales: Ancylistaceae) includes common aphid pathogens but causes sporadic mycosis worldwide. This epizootiological opportunism was explored herein by examining the potential of mycosis transmission in the progeny colonies of 513 Myzus persicae alates as disseminators of C. obscurus often infecting aphids. The alates exposed to spore showers were flown for 2.05 (0.01,8.95) km on flight mills and then reared individually on cabbage at 20,23°C for 14 day colonization. All truly infected alates were mycosed within 6 days and averagely left 3.9 (0,15) nymphs while those uninfected produced 11.6 (0,35) nymphs during the same period. Secondary and tertiary infections occurred only in 16.2% and 4.8% of the progeny colonies of the mycosed alates respectively, due to c. 60% of the cadavers forming resting spores. Most of the contagious infections appeared on days 4,8 after colonization and no more occurred from day 11 onwards. Trends of colony sizes (last-day averaging 51.5 aphids) and mycosis transmission (sixth-day maximum 6.3%) fit well to logistic (r 2 = 0.99) and Gompertz growth models (r 2 = 0.91) respectively. The results confirm that the opportunism of C. obscurus stems from depression of contagious infection after dissemination by host alates and suggest that it be overwhelmed by the prevalence of other non-resting fungal species. [source]


    Vertical distribution and behaviour of shrimp Pandalus borealis larval stages in thermally stratified water columns: laboratory experiment and field observations

    FISHERIES OCEANOGRAPHY, Issue 5 2006
    PATRICK OUELLET
    Abstract By combining field data and laboratory observations of larvae in a simulated thermal gradient, we described the ontogenetic changes in vertical distribution and behaviour of early stages of shrimp Pandalus borealis in thermally stratified water columns. Both in the laboratory and at stations in the north-western Gulf of St Lawrence, the first two larval stages appear to actively select and maintain a position in the upper layer of warmer temperatures, within the thermocline and above the cold (<1°C) intermediate layer. Stage III larvae were distributed deeper in the water column and in colder waters than the previous two stages. Stage IV and V larvae showed the highest degree of swimming activity in the laboratory and a much wider range (from surface to ,200 m) in vertical distribution in the field. The shift to deeper waters and settlement to the bottom habitat appears to happen after the fifth moult, at stage VI. We propose that the pattern of vertical distribution in the field reflects the adjustment of the different developmental stages to the distribution of preferred prey. The description of the ontogenetic change in the vertical distributions and movements of early stages of P. borealis should be valuable information for future attempts to model larval transport and dispersion, and for detecting settlement/recruitment areas using 3D ocean circulation models. The identification of the thermal habitat of the different larval stages and the timing for settlement at the bottom also provides important information for the development of temperature-dependent growth models up to the first juvenile stages. [source]


    Thermal performance of juvenile Atlantic Salmon, Salmo salar L.

    FUNCTIONAL ECOLOGY, Issue 6 2001
    B. JONSSON
    Summary 1,Experimental data for maximum growth and food consumption of Atlantic Salmon (Salmo salar L.) parr from five Norwegian rivers situated between 59 and 70°N were analysed and modelled. The growth and feeding models were also applied to groups of Atlantic Salmon growing and feeding at rates below the maximum. The data were fitted to the Ratkowsky model, originally developed for bacterial growth. 2,The rates of growth and food consumption varied significantly among populations but the variation appeared unrelated to thermal conditions in the river of population origins. No correlation was found between the thermal conditions and limits for growth, thermal growth optima or maximum growth, and hypotheses of population-specific thermal adaptation were not supported. Estimated optimum temperatures for growth were between 16 and 20 °C. 3, Model parameter estimates differed among growth-groups in that maximum growth and the performance breadth decreased from fast to slow growing individuals. The optimum temperature for growth did not change with growth rate. 4, The model for food consumption (expressed in energy terms) peaked at 19,21 °C, which is only slightly higher than the optimal temperature for growth. Growth appeared directly related to food consumption. Consumption was initiated ,2 °C below the lower temperature for growth and terminated ,1·5 °C above the upper critical temperature for growth. Model parameter estimates for consumption differed among growth-groups in a manner similar to the growth models. 5,By combining the growth and consumption models, growth efficiencies were estimated. The maximum efficiencies were high, 42,58%, and higher in rivers offering hostile than benign feeding and growth opportunities. [source]


    On the measurement of growth with applications to the modelling and analysis of plant growth

    FUNCTIONAL ECOLOGY, Issue 2 2000
    Roderick M. L.
    Abstract 1.,In this paper, a theoretical framework for the analysis of growth is described. Growth is equated with change in volume (V) and the growth rate is given by the equation; dV/dt = (dm/dt)(1/,) , (d,/dt)(m/,2) where m is the mass and , the density. The volume is inclusive of internal air spaces. 2.,The second term of the growth equation (see above) can be ignored if density is constant over time. Data for humans (and presumably other large animals) show that while composition changes over time, the density is approximately constant at about that of water. In that case, the growth rate can be estimated from measures of the rate of change of mass. However, the density of plants is variable (c. 0·4,1·2 g cm,3) and measures of mass and density are necessary to analyse plant growth. 3.,To use the theory as the basis of plant growth models, it is necessary to develop simple methods for estimating the surface area of roots, stems and leaves assuming that the mass and volume are known. A literature review found that the surface area to volume ratios of leaves and roots generally increase with the mass concentration of water. Theoretical arguments are used to predict that in woody stems, the situation should be reversed such that the surface area to volume ratio increases with the mass concentration of dry matter. Those relationships should be very useful in the development of plant growth models. 4.,Measures of plant dry mass and estimates of the rate of change in dry mass are shown to be very difficult to interpret because of differences in the mass concentration of dry matter between individuals and over time. 5.,It is concluded that measures of mass and density will be necessary before plant growth analysis can achieve its full potential. A framework for extending the theory to include the forces necessary for growth to occur is described. [source]


    On the Dynamics of Basic Growth Models: Ratio Stability vs.

    GERMAN ECONOMIC REVIEW, Issue 4 2009
    Convergence, Divergence in State Space
    Balanced growth; convergence; divergence; state space dynamics; ratio stability Abstract. We show for a class of basic growth models that convergence in ratios does not imply the pathwise convergence to the corresponding balanced growth path in the state space. We derive conditions on parameters and on the elasticity of the savings function for convergence or divergence and apply our results to the Solow model, an augmented Solow model as well as to an optimal growth model. An implication for the convergence debate is that two economies that differ only in the initial capital stock and converge in per capita terms might diverge to infinity in absolute terms. [source]


    Effectiveness versus Efficiency: Growth-Accelerating Policies in a Model of Growth without Scale Effects

    GERMAN ECONOMIC REVIEW, Issue 3 2006
    Bettina Büttner
    Endogenous growth; scale effects; welfare Abstract. Recent R&D growth models without strong scale effects imply that long-run growth rates depend only on parameters that are usually taken to be exogenous. However, integrating human capital accumulation into models of this type, Arnold (2002) demonstrates that subsidizing education accelerates growth. The present paper addresses welfare issues in Arnold's model. The main theoretical finding of the paper is that a system of subsidies that implements the optimal balanced growth path as a decentralized equilibrium includes zero subsidies to education, while R&D activity should be either subsidized or taxed. To shed further light on the latter result, the model is calibrated and it turns out that along the balanced growth path, the decentralized economy underinvests in R&D, i.e. R&D activities should be subsidized. [source]


    Stemwood volume increment changes in European forests due to climate change,a simulation study with the EFISCEN model

    GLOBAL CHANGE BIOLOGY, Issue 4 2002
    Gert-Jan Nabuurs
    Abstract This paper presents the results of a modelling study of future net annual increment changes in stemwood of European forests owing to climate change. Seven process-based growth models were applied to 14 representative forest sites across Europe under one climate change scenario. The chosen scenario was the HadCM2 run, based on emission scenario IS92a, and resulted in an increase in mean temperature of 2.5 °C between 1990 and 2050, and an increase in annual precipitation of 5,15%. The information from those runs was incorporated in a transient way in a large-scale forest resource scenario model, EFISCEN (European forest information scenario). European scale forest resource projections were made for 28 countries covering 131.7 million ha of forest under two management scenarios for the period until 2050. The results showed that net annual increments in stemwood of European forests under climate change will further increase with an additional 0.9 m3 ha,1 y,1 in 2030 compared to the ongoing increase under a current climate scenario, i.e. an extra 18% increase. After 2030 the extra increment increase is reduced to 0.79 m3 ha,1 y,1 in 2050. Under climate change, absolute net annual increments will increase from the present 4.95, on average for Europe, to 5.93 m3 ha,1 y,1 in 2025. After 2025, increments in all scenarios start to decline owing to ageing of the forest and the high growing stocks being reached. The results of the present study are surrounded by large uncertainties. These uncertainties are caused by unknown emissions in the future, unknown extent of climate change, uncertainty in process-based models, uncertainty in inventory data, and uncertainty in inventory projection. Although the results are thus not conclusive, climate change may lead to extra felling opportunities in European forests of 87 million m3y,1. Because Europe's forests are intensively managed already, management may adapt to climate change relatively easily. However, this study also indicates that climate change may lead to a faster build-up of growing stocks. That may create a less stable forest resource in terms of risks to storm damage. [source]


    Evaluation of six process-based forest growth models using eddy-covariance measurements of CO2 and H2O fluxes at six forest sites in Europe

    GLOBAL CHANGE BIOLOGY, Issue 3 2002
    K. Kramer
    Abstract Reliable models are required to assess the impacts of climate change on forest ecosystems. Precise and independent data are essential to assess this accuracy. The flux measurements collected by the EUROFLUX project over a wide range of forest types and climatic regions in Europe allow a critical testing of the process-based models which were developed in the LTEEF project. The ECOCRAFT project complements this with a wealth of independent plant physiological measurements. Thus, it was aimed in this study to test six process-based forest growth models against the flux measurements of six European forest types, taking advantage of a large database with plant physiological parameters. The reliability of both the flux data and parameter values itself was not under discussion in this study. The data provided by the researchers of the EUROFLUX sites, possibly with local corrections, were used with a minor gap-filling procedure to avoid the loss of many days with observations. The model performance is discussed based on their accuracy, generality and realism. Accuracy was evaluated based on the goodness-of-fit with observed values of daily net ecosystem exchange, gross primary production and ecosystem respiration (gC m,2 d,1), and transpiration (kg H2O m,2 d,1). Moreover, accuracy was also evaluated based on systematic and unsystematic errors. Generality was characterized by the applicability of the models to different European forest ecosystems. Reality was evaluated by comparing the modelled and observed responses of gross primary production, ecosystem respiration to radiation and temperature. The results indicated that: Accuracy. All models showed similar high correlation with the measured carbon flux data, and also low systematic and unsystematic prediction errors at one or more sites of flux measurements. The results were similar in the case of several models when the water fluxes were considered. Most models fulfilled the criteria of sufficient accuracy for the ability to predict the carbon and water exchange between forests and the atmosphere. Generality. Three models of six could be applied for both deciduous and coniferous forests. Furthermore, four models were applied both for boreal and temperate conditions. However, no severe water-limited conditions were encountered, and no year-to-year variability could be tested. Realism. Most models fulfil the criterion of realism that the relationships between the modelled phenomena (carbon and water exchange) and environment are described causally. Again several of the models were able to reproduce the responses of measurable variables such as gross primary production (GPP), ecosystem respiration and transpiration to environmental driving factors such as radiation and temperature. Stomatal conductance appears to be the most critical process causing differences in predicted fluxes of carbon and water between those models that accurately describe the annual totals of GPP, ecosystem respiration and transpiration. As a conclusion, several process-based models are available that produce accurate estimates of carbon and water fluxes at several forest sites of Europe. This considerable accuracy fulfils one requirement of models to be able to predict the impacts of climate change on the carbon balance of European forests. However, the generality of the models should be further evaluated by expanding the range of testing over both time and space. In addition, differences in behaviour between models at the process level indicate requirement of further model testing, with special emphasis on modelling stomatal conductance realistically. [source]


    The relationship between tiller appearance in spring and contribution to dry-matter yield in perennial ryegrass (Lolium perenne L.) cultivars differing in heading date

    GRASS & FORAGE SCIENCE, Issue 2 2005
    A. S. Laidlaw
    Abstract The relative contribution of tillers present in April and those appearing in consecutive periods in spring was assessed for perennial ryegrass cultivars in the three maturity groups (early, intermediate- and late-heading). Each group was represented by two diploid and one tetraploid cultivar each in plots in their third (2000) and fourth (2001) harvest years in three replicated blocks receiving an average of 325 kg N ha,1 and cut seven (in 2001) or eight (in 2000) times annually. ,Main' tillers and their daughters were marked with colour-coded PVC-covered wire loops in early April as were daughters which appeared in consecutive periods between harvests, the loop colour identifying the period of origin of the tiller. Tillers were harvested at cutting height (5 cm) before the plots were harvested and the herbage from tillers with the same colour code bulked per plot. Tillers were identified retrospectively as ,reproductive' if they had been decapitated at the previous harvest. Dry-matter yield was higher in the early than late-heading cultivars in April and early May but this was reversed in harvests in late May and June. The early heading group had a lower lamina content than the late-heading group during reproduction growth, both due to the reproductive tillers (mainly those which overwintered) having a lower leaf content and to their being fewer and smaller vegetative tillers during the reproductive phase than for the late-heading group. Turnover of tillers was high in spring due to decapitation of reproductive tillers and rapid post-flowering tillering. This was particularly pronounced in the early heading group which also had slightly more tillers marked in April which were subsequently decapitated than in the other maturity groups, i.e. 0·56 compared with 0·44 for the late-maturing group. Mean ratios of rate of death: rate of tillering for 3 years (1999,2001) for the early and late-heading groups were 0·8 and 0·4, respectively, for April,May and 1·1 and 2·4, respectively, for June indicating the different patterns in tiller turnover for the two extreme maturity groups. Information on tiller origin and contribution to yield can be used to refine tiller-based grass growth models. [source]


    Innovation and Regional Growth in the Enlarged Europe: The Role of Local Innovative Capabilities, Peripherality, and Education

    GROWTH AND CHANGE, Issue 4 2005
    RICCARDO CRESCENZI
    ABSTRACT In this paper, a formal model for the relationship between innovation and growth in European Union regions is developed drawing upon the theoretical contribution of the systems of innovation approach. The model combines the analytical approach of the regional growth models with the insights of the systemic approach. The cross-sectional analysis, covering all the Enlarged Europe (EU-25) regions (for which data are available), shows that regional innovative activities (for which a specific measure is developed) play a significant role in determining differential regional growth patterns. Furthermore, the model sheds light on how geographical accessibility and human capital accumulation, by shaping the regional system of innovation, interact (in a statistically significant way) with local innovative activities, thus allowing them to be more (or less) effectively translated into economic growth. The paper shows that an increase in innovative effort is not necessarily likely to produce the same effect in all EU-25 regions. Indeed, the empirical analysis suggests that in order to allow innovative efforts in peripheral regions to be as productive as in core areas, they need to be complemented by huge investments in human capital. [source]


    On optimal growth models when the discount factor is near 1 or equal to 1

    INTERNATIONAL JOURNAL OF ECONOMIC THEORY, Issue 1 2006
    Cuong Le Van
    C61; O41 The aim of this paper is to fill the gap between intertemporal growth models when the discount factor is close to one and when it equals one. We show that the value function and the policy function are continuous with respect both to the discount factor, ,, and the initial stock of capital, x0. We prove that the optimal policy g,(x0) is differentiable and that Dg,(x0) is continuous with respect to (,, x0). As a by-product, a global turnpike result is proved. [source]


    Production externalities and local dynamics in discrete-time multi-sector growth models with general production technologies

    INTERNATIONAL JOURNAL OF ECONOMIC THEORY, Issue 4 2005
    Kazuo Nishimura
    D90; O41 The present paper examines the dynamic properties of discrete-time, multi-sector growth models in the presence of sector-specific externalities. It extends the literature by allowing for multiple capital good sectors with general social constant returns production technologies. We establish conditions for the steady-state equilibrium to be locally determinate or locally indeterminate, depending crucially on the ratios of the social to private marginal products and the number of capital good sectors. We show that when the ratios of the social to private marginal products are uniform across all sectors, the steady state is always locally determinate in a two-sector model, although local indeterminacy might still arise when the economy features more than two sectors. [source]


    Description of growth by simple versus complex models for Baltic Sea spring spawning herring

    JOURNAL OF APPLIED ICHTHYOLOGY, Issue 1 2001
    J. Gröger
    The objective was to find a length,growth model to help differentiate between herring stocks (Clupea harengus l.) when their length,growth shows systematically different patterns. The most essential model restriction was that it should react robustly against variations in the underlying age range which varies not only over time but also between the different herring stocks. Because of the limited age range, significance tests as well as confidence intervals of the model parameters should allow a small sample restriction. Thus, parameter estimation should be of an analytical rather than asymptotic nature and the model should contain a minimum set of parameters. The article studies the comparative characteristics of a simple non-asymptotic two-parameter growth model (allometric length,growth function, abbreviated as ALG model) in contrast to higher parametric and more complex growth models (logistic and von-Bertalanffy growth functions, abbreviated as LGF and VBG models). An advantage of the ALG model is that it can be easily linearized and the growth coefficients can be directly derived as regression parameters. The intrinsic ALG model linearity makes it easy to test restrictions (normality, homoscedasticity and serial uncorrelation of the error term) and to formulate analytic confidence intervals. The ALG model features were exemplified and validated by a 1995 Baltic spring spawning herring (BSSH) data set that included a 12-year age range. The model performance was compared with that of the logistic and the von-Bertalanffy length,growth curves for different age ranges and by means of various parameter estimation techniques. In all cases the ALG model performed better and all ALG model restrictions (no autocorrelation, homoscedasticity, and normality of the error term) were fulfilled. Furthermore, all findings seemed to indicate a pseudo-asymptotic growth for BSSH. The proposed model was explicitly derived for of herring length-growth; the results thus should not be generalized interspecifically without additional proof. [source]


    Effects of climate on the growth of exotic and indigenous trees in central Zambia

    JOURNAL OF BIOGEOGRAPHY, Issue 1 2005
    E. N. Chidumayo
    Abstract Aim, Climate change has far-reaching effects on species and ecosystems. The aims of this study were to determine how climate factors affect the growth pattern of indigenous and exotic trees in Zambia and to predict tree growth responses to a warmer climate with the use of mathematical models. Location, Two savanna sites in central Zambia. Methods, Diameter at breast height (1.3 m above ground, d.b.h.) of 91 permanently marked trees belonging to three indigenous and four exotic species was measured fortnightly for periods of 1,2 years from 1998 to 2003. Correlation and regression analysis was used to determine the effect of climate factors (minimum, maximum and average temperature and rainfall) on monthly daily d.b.h. increment of each species. Regression models were used to predict the growth behaviour of trees under a 0.5 °C warmer climate. Results, Interactions between temperature and rainfall explained 60,98% of the variation in d.b.h. increment in all the tree species, except the exotic Eucalyptus grandis. For deciduous species, stem expansion was delayed by 2,12 weeks following leaf-flush and d.b.h. increment peaked during the rainy season. Evergreen and deciduous species could not be separated on the basis of annual d.b.h. increment because the higher growth rates of deciduous species compensated for the shorter growing period. Mathematical models predicted slight changes in d.b.h. growth pattern under a 0.5 °C warmer climate in five of the seven species. Significant changes in d.b.h. growth patterns were predicted in the indigenous Bridelia micrantha and exotic Gmelina arborea under a warmer climate. However, models failed to adequately represent potential soil water stress that might result from changes in tree growth patterns and a warmer climate. Main conclusions, Climate factors explained a large proportion of the variation in diameter growth of both indigenous and exotic trees, rendering it possible to model tree growth patterns from climate data. Tree growth models suggest that a rise in temperature of 0.5 °C is unlikely to induce significant changes in the growth behaviour of the majority of the studied species. However, because the growth behaviour of some species may be substantially affected by climate change, it is recommended that strategies for the future production of such climate-sensitive trees should incorporate aspects of climate change. [source]


    H-methods in applied sciences

    JOURNAL OF CHEMOMETRICS, Issue 3-4 2008
    Agnar Höskuldsson
    Abstract The author has developed a framework for mathematical modelling within applied sciences. It is characteristic for data from ,nature and industry' that they have reduced rank for inference. It means that full rank solutions normally do not give satisfactory solutions. The basic idea of H-methods is to build up the mathematical model in steps by using weighing schemes. Each weighing scheme produces a score and/or a loading vector that are expected to perform a certain task. Optimisation procedures are used to obtain ,the best' solution at each step. At each step, the optimisation is concerned with finding a balance between the estimation task and the prediction task. The name H-methods has been chosen because of close analogy with the Heisenberg uncertainty inequality. A similar situation is present in modelling data. The mathematical modelling stops, when the prediction aspect of the model cannot be improved. H-methods have been applied to wide range of fields within applied sciences. In each case, the H-methods provide with superior solutions compared to the traditional ones. A background for the H-methods is presented. The H-principle of mathematical modelling is explained. It is shown how the principle leads to well-defined optimisation procedures. This is illustrated in the case of linear regression. The H-methods have been applied in different areas: general linear models, nonlinear models, multi-block methods, path modelling, multi-way data analysis, growth models, dynamic models and pattern recognition. Copyright © 2008 John Wiley & Sons, Ltd. [source]


    Effects of size, competition and altitude on tree growth

    JOURNAL OF ECOLOGY, Issue 5 2007
    DAVID A. COOMES
    Summary 1,Understanding the factors influencing tree growth is central to forest ecology because of the significance of growth to forest structure and biomass. One of the simplest, yet most controversial growth models, proposed by Enquist and colleagues, predicts that stem-diameter growth scales as the one-third power of stem diameter. Recent analyses of large-scale data sets have challenged the generality of this theory and highlighted the influence of resource competition on the scaling of growth with size. 2Here we explore the factors regulating the diameter growth of 3334 trees of mountain beech (Nothofagus solandri var. cliffortioides) growing in natural single-species forests in New Zealand. Maximum-likelihood modelling was used to quantify the influences of tree size, altitude, the basal area of taller neighbours (BL) and the basal area of all neighbours (BT) on growth. Our interpretation of the models assumed that taller neighbours compete for light whereas all neighbours compete for nutrients. 3The regression analyses indicate that competition for light has a strong influence on the growth of small trees, whereas competition for nutrients affects trees of all sizes. These findings are consistent with experimental manipulation studies showing that competition for light and nutrients inhibits the growth of small mountain beech trees, and fertilizer application studies showing that nitrogen limits the growth of large trees. 4Tree growth declined with altitude. The regression analyses suggest that the intensity of light competition also declines with altitude, when trees with similar BT and BL values were compared along the gradient. These results are consistent with observations that trees become stunted and have more open canopies at high altitudes. 5Our study is the first to build the effects of competition and environment into Enquist's model of tree growth. We show that competitive interactions alter the scaling of mean growth rate with size, whereas altitude does not influence the scaling of potential growth rate with size. [source]


    PRODUCTIVE GOVERNMENT EXPENDITURE AND ECONOMIC GROWTH

    JOURNAL OF ECONOMIC SURVEYS, Issue 4 2009
    Andreas Irmen
    Abstract We provide a comprehensive survey of the recent literature on the link between productive government expenditure and economic growth. We show that an understanding of the core results and the ensuing contributions can be gained from the study of their respective Euler equations. We argue that the existing literature incorporates many relevant aspects; however, policy recommendations tend to hinge on several knife-edge assumptions. Therefore, future research ought to focus more on idea-based endogenous growth models to check the robustness of policy recommendations. Moreover, the inclusion of hitherto unexplored types of government expenditure, e.g. on the ,rule of law', would be desirable. [source]


    Mathematical modeling of appendicular bone growth in glaucous-winged gulls

    JOURNAL OF MORPHOLOGY, Issue 1 2009
    James L. Hayward
    Abstract Development of locomotor activity is crucial in tetrapods. In birds, this development leads to different functions for hindlimbs and forelimbs. The emergence of walking and flying as very different complex behavior patterns only weeks after hatching provides an interesting case study in animal development. We measured the diaphyseal lengths and midshaft diameters of three wing bones (humerus, ulna, and carpometacarpus) and three leg bones (femur, tibiotarsus, and tarsometatarsus) of 79 juvenile (ages 0,42 days) and 13 adult glaucous-winged gulls (Larus glaucescens), a semiprecocial species. From a suite of nine alternative mathematical models, we used information-theoretic criteria to determine the best model(s) for length and diameter of each bone as a function of age; that is, we determined the model(s) that obtained the best tradeoff between the minimized sum of squared residuals and the number of parameters used to fit the model. The Janoschek and Holling III models best described bone growth, with at least one of these models yielding an R2 , 0.94 for every dimension except tarsometatarsus diameter (R2 = 0.87). We used the best growth models to construct accurate allometric comparisons of the bones. Early maximal absolute growth rates characterize the humerus, femur, and tarsometatarsus, bones that assume adult-type support functions relatively early during juvenile development. Leg bone lengths exhibit more rapid but less sustained relative growth than wing bone lengths. Wing bone diameters are initially smaller than leg bone diameters, although this relationship is reversed by fledging. Wing bones and the femur approach adult length by fledging but continue to increase in diameter past fledging; the tibiotarsus and tarsometatarsus approach both adult length and diameter by fledging. In short, the pattern of bone growth in this semiprecocial species reflects the changing behavioral needs of the developing organism. J. Morphol., 2009. © 2008 Wiley-Liss, Inc. [source]


    Fabrication and Characterization of Cordierite/Zircon Composites by Reaction Sintering: Formation Mechanism of Zircon

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2002
    En-Hai Sun
    The formation mechanism of ZrSiO4 in the cordierite-ZrO2 system was studied in the temperature range of 1250° to 1400°C by X-ray diffraction analysis and discussed by analyzing experimental data using some reported reaction models. Nuclei growth models were found to describe the reaction well, and a satisfactory fit was obtained by applying the Avrami equation to estimate the reaction rate constant ,. Different values of the time exponent m were obtained at different temperatures: 0.32 at 1250°C, 0.34 at 1300°C, 0.39 at 1350°C, and 0.49 at 1400°C. The results indicate that there is a progressive change in reaction mechanism. [source]


    Estimating the growth models of news stories on disasters

    JOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 9 2009
    Jiuchang Wei
    Understanding the growth models of news stories on disasters is a key issue for efficient disaster management. This article proposes a method to identify three growth models: the Damped Exponential Model, the Normal Model, and the Fluctuating Model. This method is proven to be valid using the 112 disasters occurring between 2003 and 2008. The factors that influence the likelihood of the growth models include disaster types, newsworthy material, disaster severity, and economic development of the affected area. This article suggests that disaster decision-makers can identify the respective likelihood of the three growth models of news stories when a disaster happens, and thereby implement effective measures in response to the disaster situation. [source]


    Tree growth in an African woodland savanna affected by disturbance

    JOURNAL OF VEGETATION SCIENCE, Issue 3 2006
    R.M. Holdo
    Abstract: Questions: How does tree growth in a tropical woodland savanna vary as a function of size, and how is it affected by competition from neighbours, site attributes, and damage caused by disturbance? Location: western Zimbabwe. Methods: Trees of common species were tagged, mapped, and measured annually between 2001 and 2003 in a Kalahari sand woodland savanna. Diameter increments were analysed with mixed model regressions for the largest ramet in each genet. Stem diameter and damage, soil texture, and indices of competition at multiple spatial scales were used as covariates. Results: Stem diameter increased initially and then declined as a function of size in undamaged trees, which grew faster than damaged trees. Growth in damaged trees declined with size. No site differences were detected, and there was evidence for between-tree competition on growth only in the fastest-growing species, Brachystegia spiciformis. In several species the growth rate of the largest ramet increased as a function of the basal area of secondary ramets, contrary to expectations. For many species, the growth models showed poor explanatory power. Conclusions: Growth in Kalahari sand savanna trees varies as a function of size and changes in tree architecture caused by disturbance agents such as fire, frost, and elephant browsing. Disturbance may thus play an important role on vegetation dynamics through its effects on growth in the post-disturbance phase. Growth is highly stochastic for some species in this system, and more deterministic in others. It is hypothesized that this dichotomy may be driven by differences in rooting depth among species. [source]


    GROWTH OF BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) FROM THE INDIAN RIVER LAGOON SYSTEM, FLORIDA, U. S. A.

    MARINE MAMMAL SCIENCE, Issue 2 2002
    Megan K. Stolen
    Abstract Gompertz growth models were fitted to total lengths and ages from tooth sections of 199 stranded bottlenose dolphins (Tursiops truncatus) from the Indian River Lagoon system, eastern Florida. Based on the model, dolphins from this population are estimated to be born at 119 cm and reach asymptotic length at 250 cm. No apparent pubescent growth acceleration was noted for either sex. Males appeared to grow to slightly longer lengths than females. There were small size differences between Indian River dolphins and those in Texas and Sarasota, indicating general size similarities between North Atlantic and Gulf of Mexico bottlenose dolphins stocks. [source]


    The metallographic cooling rate method revised: Application to iron meteorites and mesosiderites

    METEORITICS & PLANETARY SCIENCE, Issue 1 2001
    W. D. HOPFE
    This revision incorporates a better fit to the ,/, + , phase boundary and to the ,/, + , phase boundary particularly below the monotectoid temperature of 400 °C. A reevaluation of the latest diffusivities for the Fe-Ni system as a function of Ni and P content and temperature is made, particularly for kamacite diffusivity below the paramagnetic to ferromagnetic transition. The revised simulation model is applied to several iron meteorites and several mesosiderites. For the mesosiderites we obtain a cooling rate of 0.2 °C/Ma, about 10x higher than the most recent measured cooling rates. The cooling rate curves from the current model do not accurately predict the central nickel content of taenite halfwidths smaller than ,10 ,m. This result calls into question the use of conventional kamacite growth models to explain the microstructure of the mesosiderites. Kamacite regions in mesosiderites may have formed by the same process as decomposed duplex plessite in iron meteorites. [source]


    pedagog: software for simulating eco-evolutionary population dynamics

    MOLECULAR ECOLOGY RESOURCES, Issue 3 2010
    JASON A. COOMBS
    Abstract pedagog is a Windows program that can be used to determine power for, and validate inferences drawn from, eco-evolutionary studies. It models dynamics of multiple populations and their interactions through individual-based simulations while simultaneously recording genotype, pedigree and trait information at the individual level. pedagog also allows for specification of heritable traits, natural and sexual selection acting upon those traits, population sampling schemes and incorporation of genetic and demographic errors into the output. Overall, parameters can be specified for genetic diversity, demographics, mating design, genetic and demographic errors, individual growth models, trait heritability and selection, and output formatting. Demographic parameters can be either age or function based, and all parameters can be drawn from 12 statistical distributions where appropriate. Simulation results can be automatically formatted for 57 existing software programs to facilitate postsimulation analyses. pedagog is freely available for download at https://bcrc.bio.umass.edu/pedigreesoftware/. [source]


    ACCOUNTING FOR TEMPERATURE IN PREDATOR FUNCTIONAL RESPONSES

    NATURAL RESOURCE MODELING, Issue 4 2007
    J. DAVID LOGAN
    ABSTRACT. A rational mechanism that integrates temperature-mediated activity cycles into standard predator functional responses is presented. Daily temperature variations strongly influence times that predators can search for prey, and they affect the activity periods of prey, thereby modifying their detection by predators. Thus, key parameters in the functional response, the search time and the detection, become temperature-dependent. These temperature mediated responses are included in discrete-time population growth models, and it is shown how environmental temperature variations, such as those that may occur under global climate change, can affect population levels. As an illustration, a logistic growth model with a stochastic, temperature-dependent predation term is examined, and the response to both average temperature levels and temperature variability is quantified. We infer, through simulations, that predation and prey abundance are strongly affected by mean temperature, temperature amplitudes, and increasing uncertainty in predicting temperature levels and variation, thus confirming many qualitative conclusions in the ecological literature. In particular, we show that increased temperature variability increases oscillations in the system and leads to increased probability of extinction of the prey. [source]