Thèses : « Corporations – Growth – Mathematical models »

1

Mohd, Jaffar Mai. « Mathematical models of hyphal tip growth ». Thesis, University of Dundee, 2012. https://discovery.dundee.ac.uk/en/studentTheses/140f9a81-12ca-4337-a311-2f82441f1ea6.

Texte intégral

Résumé :

Filamentous fungi are important in an enormous variety of ways to our life, with examples ranging from bioremediation, through the food and drinks industry to human health. These organisms can form huge networks stretching metres and even kilometres. However, their mode of growth is by the extension of individual hyphal tips only a few microns in diameter. Tip growth is mediated by the incorporation of new wall building materials at the soft apex. Just how this process is controlled (in fungi and in cell elongation in other organisms) has been the subject of intense study over many years and has attracted considerable attention from mathematical modellers. In this thesis, we consider mathematical models of fungal tip growth that can be classified as either geometrical or biomechanical. In every model we examine, a 2-D axisymmetric semihemisphere-like curve represents half the medial section of fungal tip geometry. A geometrical model for the role of the Spitzenkorper in the tip growth was proposed by Bartnicki-Garcia et al (1989), where a number of problems with the mathematical derivation were pointed out by Koch (2001). A suggestion is given as an attempt to revise the derivation by introducing a relationship between arc length of a growing tip, deposition of wall-building materials and tip curvature. We also consider two types of geometrical models as proposed by Goriely et al (2005). The first type considers a relationship between the longitudinal curvature and the function used to model deposition of wall-building materials. For these types of models, a generalized formulae for the tip shape is introduced, which allows localization of deposition of wall-building materials to be examined. The second type considers a relationship between longitudinal and latitudinal curvatures and the function used to model deposition of wall-building materials. For these types of models, a new formulation of the function used to model deposition of wall-building materials is introduced. Finally, a biomechanical model as proposed by Goriely et al (2010). Varying arc length of the stretchable region on the tip suggests differences in geometry of tip shape and the effective pressure profile. The hypothesis of orthogonal growth is done by focusing only on the apex of a "germ tube". Following that, it suggests that material points on the tip appear to move in a direction perpendicular to the tip either when surface friction is increased or decreased.

Styles APA, Harvard, Vancouver, ISO, etc.

2

Al-Taie, Ali Hussein Shuaa. « Continuum models for fungal growth ». Thesis, University of Dundee, 2011. https://discovery.dundee.ac.uk/en/studentTheses/9b2c14ff-c012-4541-a6ea-3ab0fea38e50.

Texte intégral

Résumé :

Fungi generally exist as unicellular organisms (yeasts) or in a vegetative state in which a mycelium, i.e. an interconnected network of tubes (hyphae) is formed. The mycelium can operate over a very large range of scales (each hypha is only a few microns in diameter, yet mycelia can be kilometres across). Fungi are of fundamental importance to many natural processes: certain species have major roles in decomposition and nutrient cycling in the soil; some form vital links with plant roots allowing nutrient transfer. Other species are essential to industrial processes: citric acid production for use in soft drinks; brewing and baking; treatment of industrial effluent and ground toxins. Unfortunately, certain species can cause devastating damage to crops, serious disease in humans or can damage building materials. In this thesis we constructed new models for the development of fungal mycelia. At this scale, partial differential equations representing the interaction of biomass with the underlying substrate is the appropriate choice. Models are essentially based on those derived by Davidson and co workers (see e.g. Boswell et al.(2007)). These models are of a complex mathematical structure, comprising both parabolic and hyperbolic parts. Thus, their analytic and numerical properties are nontrivial. The objectives of this thesis are to: (i) obtain a solid understanding of the physiology of growth and function and the varying mathematical techniques used in model construction. (ii) revisit existing models to reinterpret the various model components in a simple form. (iii) construct models to compare the growth dynamics of different phenotype for new species to see if these "scale " appropriately.

Styles APA, Harvard, Vancouver, ISO, etc.

3

Robertson-Tessi, Mark. « Mathematical Models of Tumor Growth and Therapy ». Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/194473.

Texte intégral

Résumé :

A number of mathematical models of cancer growth and treatment are presented. The most significant model presented is of the interactions between a growing tumor and the immune system. The equations and parameters of the model are based on experimental and clinical results from published studies. The model includes the primary cell populations involved in effector-T-cell-mediated tumor killing: regulatory T cells, helper T cells, and dendritic cells. A key feature is the inclusion of multiple mechanisms of immunosuppression through the main cytokines and growth factors mediating the interactions between the cell populations. Decreased access of effector cells to the tumor interior with increasing tumor size is accounted for.The model is applied to tumors of different growth rates and antigenicities to gauge the relative importance of the various immunosuppressive mechanisms in a tumor. The results suggest that there is an optimum antigenicity for maximal immune system effect. The immunosuppressive effects of further increases in antigenicity outweigh the increase in tumor cell control due to larger populations of tumor-killing effector T cells. The model is applied to situations involving cytoreductive treatment, specifically chemotherapy and a number of immunotherapies. The results how that for some types of tumors, the immune system is able to remove any tumor cells remaining after the therapy is finished. In other cases, the immune system acts to prolong remission periods. A number of immunotherapies are found to be ineffective at removing a tumor burden alone, but offer significant improvement on therapeutic outcome when used in combination with chemotherapy.Two simplified classes of cancer models are also presented. A model of cellular metabolism is formulated. The goal of the model is to understand the differences between normal cell and tumor cell metabolism. Several theories explaining the Crabtree Effect, hereby tumor cells reduce their aerobic respiration in the presence of glucose, have been put forth in the literature; the models test some of these theories, and examine their plausibility.A model of elastic tissue mechanics for a cylindrical tumor growing within a ductal membrane is used to determine the buildup of residual stress due to growth. These results can have possible implications for tumor growth rates and morphology.

Styles APA, Harvard, Vancouver, ISO, etc.

4

Jaroudi, Rym. « Inverse Mathematical Models for Brain Tumour Growth ». Licentiate thesis, Linköpings universitet, Tekniska fakulteten, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-141982.

Texte intégral

Résumé :

We study the following well-established model of reaction-diffusion type for brain tumour growth: $\begin{equation} \left\{\begin{array}{rcll} \partial_{t}u - div (D(x) \nabla u) - f(u) &=& 0,& \mbox{in }\Omega\times(0,T)\\ u(0) & = &\varphi,&\mbox{in }\Omega\\ D\nabla u\cdot n &=&0,& \mbox{on }\partial\Omega\times(0,T) \end{array}\right. \nonumber \end{equation}$ This equation describes the change over time of the normalised tumour cell density u as a consequence of two biological phenomena: proliferation and diffusion. We discuss a mathematical method for the inverse problem of locating the brain tumour source (origin) based on the reaction-diffusion model. Our approach consists in recovering the initial spatial distribution of the tumour cells $\varphi=u(0)$ starting from a later state $\psi=u(T)$ , which can be given by a medical image. We use the nonlinear Landweber regularization method to solve the inverse problem as a sequence of well-posed forward problems. We give full 3-dimensional simulations of the tumour in time on two types of data, the 3d Shepp-Logan phantom and an MRI T1-weighted brain scan from the Internet Brain Segmentation Repository (IBSR). These simulations are obtained using standard finite difference discretisation of the space and time-derivatives, generating a simplistic approach that performs well. We also give a variational formulation for the model to open the possibility of alternative derivations and modifications of the model. Simulations with synthetic images show the accuracy of our approach for locating brain tumour sources.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Wei, Yong, et 卫勇. « The real effects of S&P 500 Index additions : evidence from corporate investment ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B4490681X.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

6

Moyen, Nathalie. « Financing investment with external funds ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0019/NQ46396.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

7

Hounslow, Michael John. « A discretized population balance for simultaneous nucleation, growth and aggregation / ». Title page, summary and table of contents only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phh839.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

8

Browning, Alexander P. « Stochastic mathematical models of cell proliferation assays ». Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/110808/1/Alexander_Browning_Thesis.pdf.

Texte intégral

Résumé :

Cell proliferation assays are routinely used to study collective cell behaviour, and can be interpreted with mathematical models. In this thesis, we apply a computational Bayesian technique to calibrate stochastic discrete mathematical models of cell migration and cell proliferation in the context of a cell proliferation assay. Initially, we use a lattice-based model to explore the optimal duration of a cell proliferation assay. Next, we estimate the parameters in a lattice-free model using three independent experimental data sets. Our model is able to both describe and predict the evolution of the population and spatial structure in a cell proliferation assay.

Styles APA, Harvard, Vancouver, ISO, etc.

9

Vekstein, Daniel. « Dynamics of organizational growth in the international automobile industry ». Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186248.

Texte intégral

Résumé :

The phenomenon of organizational growth has traditionally been assumed to be indeterminate largely due to chance or accidents found in organizational worlds. This research takes up the causal processes underlying the growth (and decline) of virtually all world-class manufacturers in the international automobile industry from 1946 to 1989. Two models are developed as alternative explanations for the long-term trends observed in growth rates and their differences across firms. The models are estimated with a nonlinear method and tested through various empirical implications. The model that seems most consistent with the data shows unambiguously that they were not generated by a random or chance process but by underlying processes of collective learning, innovation, and outnovation in technologies and organizational routines. Firms that had generated different rates in these processes differed as hypothesized in their long-term growth performance. The dynamics of collective learning processes, as measured by the parameters of the model, largely explain the dynamics of organizational growth in the world automobile industry, hence, the dynamics of interorganizational competition. The results from tests of ecological hypotheses suggest that organizational ecology might benefit from the application of matrices of collective learning rates generated from interorganizational learning curves, particularly where ecology seeks to explain patterns of competition by organizational size. As shown, this research strategy is general and gauges directly interactions among organizations over long periods. It is also flexible in dealing with various levels of analysis in longitudinal and cross-sectional dimensions. As also shown, the collective learning theory, its model, and the ecology of interorganizational learning curves derived from them can help in evaluating empirically the competitive potential of firms by indicators of innovation and outnovation relative to other firms, patterns of competition (gauged by relative learning rates) among firms, and any changes of those patterns over time. Thus, the research strategy used here provides potentially useful causal analyses as well as meaningful measures on which different organizations can be compared, with each other and with themselves. These measures may also provide important benchmarks and diagnostics for strategic management.

Styles APA, Harvard, Vancouver, ISO, etc.

10

Stott, Emma Louise. « Solid tumour growth : a comparison of mathematical models and computer simulations ». Thesis, University of Bath, 1998. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285273.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

11

Egeh, Mohamud H. « Modeling corn growth, development and yield under Québec conditions ». Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21546.

Texte intégral

Résumé :

The use of crop growth simulation models such asthose incorporated into Decision Support Systems for Agrotechnology Transfer (DSSAT) are useful tools for assessing the impacts of various management practices on crop productivity. The maize growth model of DSSAT is CERES-maize. To evaluate its predictive capability under western Quebec conditions, data on corn (Zea mays L.) yield and above-ground biomass were collected from a field-scale water table management experiment conducted during the 1996 and 1997 growing seasons at St. Emmanuel, Soulanges County, Quebec. The model was calibrated using various crop growth and development data observed during the 1996 growing season. Cultivar-specific coefficients were determined during the calibration. All measured data on phenology, grain yield and biomass collected in 1997 were used for model validation.
Validation results showed good agreement between predicted and measured yields. In 1996, the Root Mean Square Error (RMSE) was 0.64 and 0.66 Mg/ha for the free drainage plots with 200 kg/ha N (FD200) and 120 kg/ha N (FD120), respectively. In 1997, the RMSE for FD200 and FD120 were 1.07 and 1.23 Mg/ha respectively. However, the model overpredicted the biomass for 1997, and grain number for both FD200 and FD120 treatments in both years. The mean difference (MD) between simulated and observed biomass at maturity was statistically significant at (P < 0.01) for both treatments. Sensitivity analyses showed that the CERES-Maize model was most sensitive to changes in air temperature. The model was also sensitive to soil water and crop genetic parameters.

Styles APA, Harvard, Vancouver, ISO, etc.

12

Parker, Reginald. « Towards a comprehensive kinetic model for step-growth polymerization ». Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/10995.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

13

Abrahamsson, Linda. « Statistical models of breast cancer tumour growth for mammography screening data ». Thesis, Uppsala universitet, Matematisk statistik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-171980.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

14

Yin, Xiaopeng 1963. « Endogenous growth, international trade and dynamics ». Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37914.

Texte intégral

Résumé :

This PhD. dissertation consists of three essays to fill some gaps in the recent research in international trade and endogenous growth theory. The first essay explores the dynamic effect of interaction of research and development (R&D) activities among countries on endogenous economic growth. It attempts to fill the gap between the current endogenous growth research focused on independent R&D activities and decision-making in the international competition and the interdependent R&D competition in reality. This paper finds that the growth rates, welfare, and investment on R&D in the world do differ between independent R&D activity and interdependent R&D activities among countries. The welfare for each country in the open-loop Nash equilibrium is higher than that of the Markov-perfect Nash equilibrium, and both are lower than that in the cooperative game. The model shows that the ability to commit turns out to make every country better off. The interesting results are that when an increase in the number of countries does increase the growth rate in the open-loop Nash equilibrium, it is very possible to have the negative effect on the growth rate in the Markov-perfect equilibrium. Particularly, the model shows that the tendency of free-ride rises with more countries in the competition. The more general models with durable physical capital, and with the endogenous rate of time preference following Uzawa-Epstein tradition, also prove these conclusions.
The second essay turns to the Samuelson-Diamond overlapping generation paradigm, a finite-horizon overlapping generations model with education proposed by Michel (1993). The focus is shifted to the effect of trade on growth. It turns out that when trade affects the formation of human capital, endogenous growth is possible even in the simplest economy with a single sector and constant returns to scale technologies, which is opposite from Boldrin's (1992) and Jones and Manuelli's (1992) results.
While the existing theory of trade under oligopolistic competition is mostly static in nature, the third essay fills this gap by modeling international trade under oligopoly in a dynamic setting. This essay adopts the dynamics in the model provided by allowing the demand curve to shift over time as a result of "habit formation". It shows that when the importing country is committing to a policy of voluntary import expansions (VIEs), in the certain condition (i.e. k > 1), VIEs can improve the global welfare, the welfare of the importing country, and the profit of both firms. So, in a sense, voluntary import expansion is truly voluntary.

Styles APA, Harvard, Vancouver, ISO, etc.

15

Murphy, Ryan John. « Mechanochemical and experimental models in mathematical biology ». Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/228428/1/Ryan%20John_Murphy_Thesis.pdf.

Texte intégral

Résumé :

Experiments that probe epithelial tissue dynamics, cell competition, and tumour growth are fundamental to understand processes in developmental biology, cancer progression and treatment. However, interpreting complex biological experiments is challenging. To address this challenge, we develop and use a range of mathematical models. First, we focus on epithelial tissue dynamics. Second, we use real-time cell cycle imaging to reveal the structure of growing tumour spheroids. We then revisit the seminal Greenspan tumour growth model and use statistical analysis to quantitatively connect it to experimental data for the first time to reveal experimental design choices that lead to reliable biological insight.

Styles APA, Harvard, Vancouver, ISO, etc.

16

Chu, Kai-cheung, et 朱啟祥. « The effects of mean reversion on dynamic corporate finance and asset pricing ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B47752762.

Texte intégral

Résumé :

This thesis aims to investigate the effects of mean reversion on dynamic corporate finance decisions and stock pricing. In Chapter 1, a continuous-time real option model of mature firm that produces product with exogenous mean reverting price is developed to study the firm’s optimal exit and leverage policies. Simulation results show that both liquidation and bankruptcy triggers are negatively related to the long run price levels, while the speed of mean reversion interacts with the long run price level to affect the firm’s exit decisions in two opposite directions depending on the level’s relative magnitude to total operating expenses (the firm’s instantaneous operation costs plus coupon payments). Regarding the leverage policy, apart from showing the static tradeoff result that firm uses more debts when the current revenues are high, the model exhibits at high long run price levels low-debt scenarios that are analogous to the pecking order prediction, suggesting that both static tradeoff and pecking order effects coexist under a mean reversion environment. Because equity values increase more vigorously with prices than debt values do, the tradeoff effect is overwhelmed and the resulting optimal leverage ratios are generally decreasing with the current price levels. Chapter 2 extends the model in Chapter 1 to derive the closed-form expression of the firm’s equity beta. Because expected stock returns are linearly related to the equity beta by model assumption, several implications to the cross-sectional behaviors of stock returns are obtained. First, it is predicted that firms with mean reverting characteristics should earn lower average returns than others without. The model further reveals the coexistence of positive book-to-market and leverage premiums to stock returns. Most importantly, due to the possession of bankruptcy option by equity holders, high distress risk stocks are expected to earn lower average returns than otherwise similar but low distress risk stocks. This provides an extra dimension to study the ‘distress premium puzzle’. Finally to verify the model predictions, empirical tests using historical market and accounting data from CRSP and COMPUSTAT are conducted, and supportive results are generally obtained.
published_or_final_version
Economics and Finance
Doctoral
Doctor of Philosophy

Styles APA, Harvard, Vancouver, ISO, etc.

17

Lima, Ernesto Augusto Bueno da Fonseca. « Phase-field models of tumor growth with angiogenesis ». Laboratório Nacional de Computação Científica, 2014. https://tede.lncc.br/handle/tede/180.

Texte intégral

Résumé :

Made available in DSpace on 2015-03-04T18:57:59Z (GMT). No. of bitstreams: 1 thesis.pdf: 5073087 bytes, checksum: f23ad1a1747577782cd9c9eab7574795 (MD5) Previous issue date: 2014-04-29
Conselho Nacional de Desenvolvimento Cientifico e Tecnologico
The development of predictive computational models of tumor initiation, growth, and decline is faced with many formidable challenges. Phenomenological models which attempt to capture the complex interactions of multiple tissue and cellular species must cope with moving interfaces of heterogeneous media and the huge uncertainties of the parameters and their evolution. They must be able to deliver predictions consistent with events that take place at cellular scales, and they must faithfully depict biological mechanisms and events that are known to be associated with various forms of cancer. In the present work, some models for the tumor behavior are presented which fall within the framework of phase-field (or diffuse-interface) models suggested by continuum mixture theory. This framework provides for the simultaneous treatment of interactions of multiple evolving species, such as tumor cells, necrotic cell cores, nutrients, and other cellular and tissue types that exist and interact in living tissue. In the present work, a hybrid phase field ten-species vascular model for the tumor growth is developed, which couples the tumor growth with sprouting through angiogenesis. The model is able to represent the branching of new vessels through coupling a discrete model for which the angiogenesis is started upon pre-defined conditions on the nutrient deprivation in the continuum model. Such conditions are represented by hypoxic cells that release tumor growth factors that ultimately trigger vascular growth. We discuss the numerical approximation of the model using mixed finite elements. We also consider an avascular stochastic six-species tumor growth model derived directly from the hybrid ten-species model. The stochasticity comes from modeling uncertainties in the parameters of the model. We perform a sensitivity analysis to identify the more relevant parameters on the tumor mass growth. The stochastic model is then developed taking into account the uncertainty of the most influential parameter. The numerical approximation of the model using Stochastic Collocation method to treat uncertainties in the nonlinear system is presented. The results of numerous numerical experiments are also presented and discussed.
Modelos matematicos e computacionais sao utilizados na compreensao de fenomenos complexos, sendo aplicados em diversas areas como engenharia, fisica e biologia. Na Medicina tem um importante papel na simulacao do tratamento e evolucao de algumas doencas, entre elas o cancer. O desenvolvimento de modelos computacionais para o crescimento tumoral se depara com desafios formidaveis. Modelos fenomenologicos que tentam capturar as complexas interacoes de multiplos tecidos e especies celulares devem lidar com interfaces em meios heterogeneos e as enormes incertezas dos parametros e suas evolucoes. Eles devem ser capazes de proporcionar predicoes consistentes com eventos que ocorrem em escalas celulares, e devem representar fielmente os mecanismos biologicos associados ao cancer. No presente trabalho, sao apresentados alguns modelos para o crescimento tumoral. Esses modelos inserem-se no ambito de modelos de campo de fase (ou interface difusiva) sugeridos pela teoria mistura. Esta metodologia preve o tratamento simultaneo de interacoes entre multiplos constituintes, como as celulas tumorais, celulas necroticas, nutrientes e outros tipos celulares e teciduais que existem e interagem em tecidos vivos. Neste trabalho, um modelo hibrido de campo de fases, de dez constituintes e desenvolvido para o crescimento tumoral vascular, que acopla o crescimento de tumores com crescimento de novos vasos sanguineos atraves da angiogenese. O modelo é capaz de representar a ramificacao de novos vasos atraves do acoplamento de um modelo discreto, no qual a angiogenese é iniciada mediante condicoes pre-definidas, relacionadas a privacao de nutrientes no modelo macroscopico. Tais condicoes sao representadas por celulas hipoxicas que liberam quimicos reponsaveis por induzir a angiogenese tumoral. A aproximacao numerica do modelo usando elementos finitos mistos é discutida. Considera-se tambem um modelo estocastico avascular de seis constituintes para o crescimento tumoral, derivado diretamente do modelo hibrido de dez constituintes. A estocasticidade vem de incertezas na modelagem dos parametros do modelo. Realiza-se uma analise de sensibilidade para identificar os parametros mais relevantes sobre o crescimento da massa tumoral. O modelo estocastico é entao desenvolvido tendo em conta a incerteza no parametro mais influente. A aproximacao numerica do modelo usando o metodo estocastico de Colocacao para tratar incertezas no sistema nao-linear é apresentada. Os resultados de varios experimentos numericos tambem sao apresentados e discutidos.

Styles APA, Harvard, Vancouver, ISO, etc.

18

Kwon, Sun Hong. « Directional growth of wind generated waves ». Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/49816.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

19

Kooner, Priya. « Mathematical modelling of tumour invasion : from biochemical networks to tissue dynamics ». Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670187.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

20

Shortt, James S. « A comparison of forest growth and yield models for inventory updating ». Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-01102009-063919/.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

21

Orme, Michelle Elaine. « The vascularization of solid tumours : mathematical models of tumour angiogenesis and vascular tumour growth ». Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362238.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

22

Wu, Hsiu-Jean. « The kinetics of solvent-mediated phase transformations ». Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/184981.

Texte intégral

Résumé :

The objectives of this work are to characterize and model the solvent-mediated phase transformation process of theophylline anhydrous crystals to the monohydrate crystals in an aqueous system. In order to model the transformation, the following processes are taken into account: (1) the dissolution kinetics of theophylline anhydrous crystals, (2) the kinetics of the formation of theophylline monohydrate nuclei, and (3) the growth kinetics of the monohydrate crystals. The driving forces for the above processes are determined from the concentration of theophylline in the solution and the solubilities of theophylline anhydrous and monohydrate. The solubilities of theophylline anhydrous and the monohydrate, and these three distinct processes along with the overall transformation phenomena were investigated in the present study. By using theophylline as a model compound we have gained some understanding of the kinetics of the solvent-mediated phase transformation between the metastable anhydrous form and the stable hydrated form of an organic compound and we were able to model the transformation process. By identifying the mechanisms for nucleation, growth of the hydrate form and the dissolution of the anhydrous form one can predict and control the transformation process. The growth kinetics of thymine monohydrate crystals at various temperatures are also investigated in the present study.

Styles APA, Harvard, Vancouver, ISO, etc.

23

Siegel, Paul B. « The relationship between changing economic structure and performance : diversification, diversity, growth, stability, and distribution impacts ». Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/40017.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

24

Lo, Pang-yuen, et 羅鵬遠. « Early childhood growth patterns and adult health indicators ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B39724864.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

25

Strandberg, Per Erik. « Mathematical models of bacteria population growth in bioreactors : formulation, phase space pictures, optimisation and control ». Thesis, Linköping University, Department of Mathematics, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2337.

Texte intégral

Résumé :

There are many types of bioreactors used for producing bacteria populations in commercial, medical and research applications.

This report presents a systematic discussion of some of the most important models corresponding to the well known reproduction kinetics such as the Michaelis-Menten kinetics, competitive substrate inhibition and competitive product inhibition. We propose a modification of a known model, analyze it in the same manner as known models and discuss the most popular types of bioreactors and ways of controlling them.

This work summarises much of the known results and may serve as an aid in attempts to design new models.

Styles APA, Harvard, Vancouver, ISO, etc.

26

Yin, Xiaopeng 1963. « The effect of economic integration on endogenous economic growth ». Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23435.

Texte intégral

Résumé :

This thesis presents a survey of the development of economic growth theory, including the latest developments in the relationship between international economic integration through international flows of goods and/or knowledge and endogenous economic growth. Based on the following literature review, a new and more reasonable model for the research and development (i.e., the R&D) sector--a sector which is considered the source of long-run growth--is offered in order to develop and improve the framework built by Rivera-Batiz and Rome (1991), i.e. the RBR model. This new model will make the RBR framework more complete and rational. In this new model, it is proved that any form of economic integration will increase the long-run rate of growth, and these results are compared with those of the RBR. Moreover, Devereux and Lapham's efforts to find some dynamic analysis along the transitional path under two different situations: knowledge flows only, and both goods and knowledge flows, are continued in the same model. It is found that when only knowledge is allowed to flow across borders, economic integration generates corner solutions for the production of the R&D sector, while this does not happen when complete goods and knowledge flows exist. However, the real balanced growth rates in these diverse situations are higher than they are in autarky.

Styles APA, Harvard, Vancouver, ISO, etc.

27

Maric, Arata Branko J. « Inflation uncertainty, monetary shocks and economic growth : evidence from Brazil, Chile, Columbia, Mexico and Peru ». Thesis, Virginia Tech, 1994. http://hdl.handle.net/10919/43001.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

28

Monette, Liza. « Numerical simulations of nucleation and growth phenomena ». Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=64053.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

29

Schmidt, Gordon 1946. « Dynamics of endogenous economic growth theory and related issues : a case study of the "Romer model" ». Monash University, Dept. of Economics, 2001. http://arrow.monash.edu.au/hdl/1959.1/8832.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

30

Adams, Matthew P. « Mathematical models of calcium and tight junctions in normal and reconstructed epidermis ». Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/81869/1/Matthew_Adams_Thesis.pdf.

Texte intégral

Résumé :

This project investigated the calcium distributions of the skin, and the growth patterns of skin substitutes grown in the laboratory, using mathematical models. The research found that the calcium distribution in the upper layer of the skin is controlled by three different mechanisms, not one as previously thought. The research also suggests that tight junctions, which are adhesions between neighbouring skin cells, cannot be solely responsible for the differences in the growth patterns of skin substitutes and normal skin.

Styles APA, Harvard, Vancouver, ISO, etc.

31

Omari, Mohamed. « Analysis of the effects of growth-fragmentation-coagulation in phytoplankton dynamics ». Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/17793.

Texte intégral

Résumé :

Thesis (MSc)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: An integro-differential equation describing the dynamical behaviour of phytoplankton cells is considered in which the effects of cell division and aggregation are incorporated by coupling the coagulation-fragmentation equation with growth, and the McKendrick-von Foerster renewal model of an age-structured population. Under appropriate conditions on the model parameters, the associated initial-boundary value problem is shown to be well posed in a physically relevant Banach space using the theory of strongly continuous semigroups of operators, the theory of perturbation of positive semigroups and the semilinear abstract Cauchy problems theory. In particular, we provide sufficient conditions for honesty of the model. Finally, the results on the effects of the growth-fragmentation-coagulation on the overall evolution of the phytoplankton population are summarised.
AFRIKAANSE OPSOMMING: ’n Integro-differensiaalvergelyking wat die dinamiese ontwikkeling van fitoplanktonselle beskryf, word beskou. Die uitwerking van seldeling en -aggregasie is geïnkorporeer deur die vergelyking van koagulasie en fragmentasie met groeiaan die McKendrick-von Foerster hernuwingsmodel van ’n ouderdomsgestruktureerde populasie te koppel. Die teorie van sterk kontinue semigroepe van operatore, steuringsteorie van positiewe semigroepe en die teorie van semilineêre abstrakte Cauchy probleme word aangewend om, onder gepaste voorwaardes met betrekking tot die model se parameters, te bewys dat die geassosieerde beginwaarde-probleem met randvoorwaardes ‘goed gestel’ is in ’n fisies relevante Banach-ruimte. In die besonder word voldoende voorwaardes vir eerlikheid van die model verskaf. Ten slotte word ’n opsomming van die resultate met betrekking tot die gekombineerde uitwerking van groei-fragmentasie- koagulasie op die gesamentlike ontwikkeling van die fitoplanktonpopulasie verskaf.

Styles APA, Harvard, Vancouver, ISO, etc.

32

Redfern, S. E. « Atomistic simulation of mineral surfaces : their structure, hydration and growth ». Thesis, University of Bath, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301964.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

33

Araujo, Robyn Patrice. « Mathematical modelling of mechanical stresses and vascular collapse in solid tumours ». Thesis, Queensland University of Technology, 2003. https://eprints.qut.edu.au/37156/6/37156_Digitised_Thesis.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

34

Jin, Wang. « Investigating the reproducibility of in vitro cell biology assays using mathematical models ». Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/109790/1/Wang_Jin_Thesis.pdf.

Texte intégral

Résumé :

In vitro cell biology assays are routinely used to study cancer spreading, drug design and tissue repair. However, issues associated with reproducibility are reported in literature. In this thesis we investigate the overlooked source of variability that affects the reproducibility of cell biology assays, using a combined mathematical and experimental approach. By calibrating mathematical models to experimental data, we find that the initial degree of confluence significantly affects cell motility. Following the similar approach, we identify the two-phase growth in scratch assays. We then propose a proliferation mechanism for lattice-based, random walk models, which accounts for biologically more realistic crowding effects. At last, we use a lattice-based, random walk model to mimic the passaging process and find that the passage number could significantly affect the wound closure in scratch assays.

Styles APA, Harvard, Vancouver, ISO, etc.

35

Pant, Sudeep Raj. « Mathematical and physical modelling of crack growth near free boundaries in compression ». University of Western Australia. School of Civil and Resource Engineering, 2005. http://theses.library.uwa.edu.au/adt-WU2005.0139.

Texte intégral

Résumé :

[Truncated abstract] The fracture of brittle materials in uniaxial compression is a complex process with the development of cracks generated from initial defects. The fracture mechanism and pattern of crack growth can be altered considerably by the presence of a free surface. In proximity of a free surface, initially stable cracks that require an increase in the load to maintain the crack growth can become unstable such that the crack growth maintains itself without requiring further increase in the load. This leads to a sudden relief of accumulated energy and, in some cases, to catastrophic failures. In the cases of rock and rock mass fracturing, this mechanism manifests itself as skin rockbursts and borehole breakouts or as various non-catastrophic forms of failure, e.g. spalling. Hence, the study of crack-boundary interaction is important in further understanding of such failures especially for the purpose of applications to resource engineering. Two major factors control the effect of the free boundary: the distance from the crack and the boundary shape. Both these factors as well as the effect of the initial defect and the material structure are investigated in this thesis. Three types of boundary shapes - rectilinear, convex and concave - are considered. Two types of initial defects - a circular pore and inclined shear cracks are investigated in homogeneous casting resin, microheterogeneous cement mixes and specially fabricated granulate material. The preexisting defects are artificially introduced in the physical model by the method of inclusion and are found to successfully replicate the feature of pre-existing defects in terms of load-deformation response to the applied external load. It is observed that the possibility of crack growth and the onset of unstable crack growth are affected by the type of initial defect, inclination of the initial crack, the boundary shape and the location of the initial defect with respect to the boundary. The initial defects are located at either the centre or edge of the sample. The stresses required for the wing crack initiation and the onset of unstable crack growth is highest for the initial cracks inclined at 35° to the compression axis, lowest at 45° and subsequently increases towards 60° for all the boundary shapes and crack locations. In the case of convex boundary, the stress of wing crack initiation and the stress of unstable crack growth are lower than for the case of rectilinear and concave boundary for all the crack inclinations and crack locations. The crack growth from a pre-existing crack in a sample with concave boundary is stable, requiring stress increase for each increment of crack growth. The stress of unstable crack growth for the crack situated at the edge of the boundary is lower than the crack located at the centre of the sample for all the crack inclinations and boundary shapes.

Styles APA, Harvard, Vancouver, ISO, etc.

36

Knecht, Billberger Magnus F. « Plant growth - stoichiometry and competition : theory development in ecosystem ecology / ». Uppsala : Dept. of Ecology and Environmental Research, Swedish University of Agricultural Sciences, 2006. http://epsilon.slu.se/200624.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

37

Onana, Eloundou Jeanne Marie. « Mathematical modelling of the stages of solid tumours growth and the nonlocal interactions in cancer invasion ». Thesis, Stellenbosch : Stellenbosch University, 2011. http://hdl.handle.net/10019.1/18056.

Texte intégral

Résumé :

Thesis (MSc)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: For solid tumours to grow and metastise, they need to pass through two distinct stages: the avascular growth phase in which the tumour remains in a limited diffusion size and the vascular growth phase where the invasion may take place. In order to accomplish the transition from the former to the latter growth phase, a solid tumour may secrete a substance known as tumour angiogenesis factor (TAF) into the surrounding tissues to stimulate its own blood vessels. Once the tumour has its own blood supply, it can invade other parts of the body destroying healthy tissues organs by secreting the matrix degrading enzymes (MDE). During the invasion, the adhesion both cell-cell and cell-matrix play an extremely important role. In this work, we review some mathematical models dealing with various stages of development of solid tumours and the resulting reaction diffusion equations are solved using the Crank-Nicolson finite differences scheme. We also present a system of reaction-diffusion-taxis partial differential equations, with nonlocal (integral) terms describing the interactions between cancer cells and the host tissue. We then investigate the local and global existence of the solution of the previous model using the semigroup method and Sobolev embeddings.
AFRIKAANSE OPSOMMING: Daar is twee afsonderlike fases nodig vir soliede kanker gewasse om te groei en kwaadaardig te word: die avaskulêre groeifase waarin die gewas tot ’n sekere diffusie grootte beperk word en die vaskulêre groei fase waar die indringing plaasvind. Ten einde die oorgang tussen die twee fases te bewerkstellig, skei die soliede gewas ân stof in die omliggende weefsel af wat bekend staan as âtumor angiogenese factorâ (TAF). Dit stimuleer die vorming van die gewas se eie bloedvate. Wanneer die gewas sy eie bloedtoevoer het, kan dit ander dele van die liggaam indring en gesonde orgaanweefsel vernietig deur die afskeiding van die âmatrix degrading enzymesâ (MDE). Gedurende hierdie proses speel die sel-sel en sel-matriks interaksies ân belangrike rol. In hierdie werk het ons ân paar wiskundige modelle vergelyk wat die verskillende stadiums van die ontwikkeling van soliede gewasse beskryf. Die gevolglike diffusiereaksie vergelykings is opgelos deur gebruik te maak van die âCrank-Nicolson finite differences schemeâ. Ons bied ook ’n stelsel van âreaction-diffusion-taxisâ, met nie-lokale (integrale) terme wat die interaksies tussen kankerselle en die gasheerweefsel beskryf. Ons stel dan ondersoek in na die lokale en globale bestaan van die oplossing van die vorige model, met behulp van die semi-groep metode en die Sobolev ingebeddings.

Styles APA, Harvard, Vancouver, ISO, etc.

38

Stamatopoulos, Nicole. « The use of ultrasound in the prediction of miscarriage, gestational trophoblastic disease and first trimester embryonic growth ». Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/28828.

Texte intégral

Résumé :

Miscarriage occurs in approximately 25% of all clinical pregnancies. Little is known as to the causes. It is commonly due to aneuploidy including gestational trophoblastic disease. Ultrasound parameters as well as serum human chorionic gonadotrophin ratios have been incorporated into algorithms. Pregnant women with any bleeding become anxious and fear they have miscarried. A mathematical model was previously developed to assess the likelihood of miscarriage in women who had had previous ultrasound demonstrating a viable intra-uterine pregnancy. Five objective variables were identified. The aim of this thesis was to internally and externally validate this model. This allows further insight into the role of ultrasound in miscarriage prediction. If a woman has had a diagnosis of gestational trophoblastic disease, this will impact when she can next conceive, follow up after every pregnancy and may progress to gestational trophoblastic neoplasia. There are features on ultrasound suggestive of gestational trophoblastic disease. Histopathology of the products of conception is the gold standard for diagnosis. Given that this is a complication of early pregnancy and at times can be mistaken for miscarriage, a secondary aim of this thesis was to assess if transvaginal ultrasound could be used as a diagnostic tool to predict gestational trophoblastic disease. There are modifiable risk factors that may lead to miscarriage or complications. Cigarette smoking is one of those; associated with pre-term birth, placental abruption, and fetal growth restriction in the second and third trimesters of pregnancy. It is not known whether the effects cigarette smoking on fetal growth can be detected as early as the first trimester. The final aim of this thesis was to evaluate the impact of cigarette smoking on first trimester embryonic growth.

Styles APA, Harvard, Vancouver, ISO, etc.

39

Hans, Richard P. « Estimating the coefficients in a system of compatible growth and yield equations for Loblolly pine ». Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/94460.

Texte intégral

Résumé :

In this thesis the five equation system of growth and yield equations originally developed by Clutter (1963) is examined. The system is redeveloped algebraically to form a truly algebraically compatible system. Three methods of estimating the coefficients were examined. In the first method, three of the equations were fitted independently using ordinary least squares; these coefficient estimates were carried through to the other equations. No consideration was given to the relationships that must exist between the equation coefficients in order for the system to be numerically consistent. In the second method the system is first developed algebraically, before any of the coefficients are estimated, resulting in a slightly different system which is truly algebraically compatible. The coefficients were estimated by fitting two of the equations, and using these estimates throughout the rest of the system. The resulting system is both numerically consistent and algebraically compatible. In the final method the relationships between the coefficients that must hold for the system to be compatible were incorporated in the coefficient estimation procedure. Seemingly unrelated regression techniques were used to estimate the coefficients. The three methods resulted in coefficient estimates that were similar, with seemingly unrelated regression producing the most efficient estimators. Prediction ability of the three methods on independent data show no method as being superior, although the seemingly unrelated regression procedure was able to reduce the total system error best.
M.S.

Styles APA, Harvard, Vancouver, ISO, etc.

40

Sutherland, Elaine Kennedy. « The effect of prescribed burning on southwestern ponderosa pine growth ». Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184954.

Texte intégral

Résumé :

Study objectives included determining whether prescribed burning affected ponderosa pine growth; mathematically modeling the growth response to burning; and determining whether forest management history affected growth response. I sampled 188 trees from two areas near Flagstaff, Arizona; one area (Brannigan Flat) had been logged and thinned, and the other (Chimney Spring) had not; both were burned in 1976. Within each study area, control and burned plots were of similar age, vigor, height, and competition index. Trees at Chimney Spring were older, less vigorous, and taller, and had a higher competition index than at Brannigan. For each tree, periodic basal area increment (PBAI) was calculated for the years 1974-1984. To determine which variable would best model growth, postfire PBAI (individual years, 1977-1984) was correlated with previous growth (average PBAI 1974-1976); crown ratio; competition index; thinning index; and diameter. Two models of growth response were developed; one oriented toward satisfying theoretical and research goals, and the other, toward management applications. Growth was modeled using stepwise multiple linear regression, and the dependent variable was postfire PBAI. Research Model independent variables were previous growth, years (climate), and treatment-year interaction, and 72% of total variance was explained. Fire affected growth significantly and negatively for two years, and then burned trees grew similarly to control trees. Management Model independent variables were crown ratio, competition index, crown ratio, subject tree diameter, year, and treatment, and 52% of total variance was explained. This model, too, indicated a slight negative effect of burning on growth. Management history was not a significant determinant of growth response. Both models validated well; the ratio of observed-to-predicted residual mean square was 1.04 and 0.91 (Research and Management Models, respectively). Thinning index was not significantly related to postfire growth, but a change in carbohydrate allocation from stem wood to crown and root expansion could have resulted in observed burning effects. Management implications include (1) short-term growth decline may result from burning, (2) management history did not affect growth response, and (3) burning impact is greatest in dense stands of small trees.

Styles APA, Harvard, Vancouver, ISO, etc.

41

Vlad, Iulian Teodor. « Mathematical Methods to Predict the Dynamic Shape Evolution of Cancer Growth based on Spatio-Temporal Bayesian and Geometrical Models ». Doctoral thesis, Universitat Jaume I, 2016. http://hdl.handle.net/10803/670303.

Texte intégral

Résumé :

The aim of this research is to observe the dynamics of cancer tumors and to develop and implement new methods and algorithms for prediction of tumor growth. I offer some tools to help physicians for a better understanding this disease and to check if the prescribed treatment have the desired results. The plan of the thesis is the following. In Chapter 1 I briefly recall some properties and classification of points processes with some examples of spatio-temporal point processes. Chapter 2 presents a short overview of the theory of Levy bases and integration with respect to such basis is given, I recall standard results about spatial Cox processes, and finally I propose different types of growth models and a new algorithm, the Cobweb, which is presented and developed based on the proposed methodology. Chapters 3, 4 and 5 are dedicated to present new prediction methods. The implementation in Matlab software comes in Chapter 6. The thesis ends with some conclusion and future research.
El objetivo de esta investigación es observar la dinámica de los tumores, desarrollar e implementarnuevos métodos y algoritmos para la predicción del crecimiento tumoral. Queremos ofrecer algunasherramientas para ayudar a los médicos a comprender y tratar esta enfermedad. Utilizando unmétodo de predicción , y comparándolo con la evolución real de un tumor, un médico puede constata si el tratamiento prescrito tiene el efecto deseado, y de acuerdo con ello, si es necesario, tomar la decisión de intervención quirúrgica. El plan de la tesis es el siguiente. En el primer capítulo recordamos brevemente algunaspropiedades y procesos de clasificación de procesos puntuales con algunos ejemplosespacio-temporales. El capítulo 2 presenta una breve descripción de la teoría de las bases de Levy y se da la integración con respecto a dicha base, recordamos resultados estándar sobre procesosespaciales de Cox, y finalmente proponemos diferentes tipos de modelos de crecimien to y un nuevo algoritmo, el Cobweb, que es presentado y desarrollado en base a la metodología propuesta. Los capítulos 3, 4 y 5 están dedicados a presentar nuevos métodos de predicción.

Styles APA, Harvard, Vancouver, ISO, etc.

42

Smith, Michael C. « Diameter and height increment and mortality functions for loblolly pine trees in thinned and unthinned plantations ». Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-03242009-040942/.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

43

Li, Zhaohui. « Monitoring biological functions of cultured tissues using microdialysis ». Thesis, University of Oxford, 2007. http://ora.ox.ac.uk/objects/uuid:f8b478fa-881e-4299-9ee5-b8ee29f37fe9.

Texte intégral

Résumé :

Continuous monitoring during tissue culture is important for the success of engineered tissue development. It is also challenging due to lack of suitable established monitoring techniques. In this study, microdialysis, a sampling technique for measuring the unbound solute concentrations in the tissues and organs of the living body, was adopted to monitor functional tissue growth in a bioreactor with explanted bovine caudal intervertebral discs (IVD) as the test tissue. Apart from cell metabolic activities, cell and tissue biological functions were investigated for the development of microdialysis for monitoring purposes. Methodologies of microdialysis with large pore size membrane probes for sampling macromolecular bio-functional markers were established. The effects of pumping methods, including 'push', 'pull' or 'push-and-pull', and the effect of the resulting transmembrane pressure on the fluid balance, and the relative recovery of small molecules and of macromolecules (proteins) were experimentally studied. The validity of the internal reference in-situ calibration was examined in detail. It was concluded that a push-and-pull system was the only effective method to eliminate fluid loss or gain. The relative recovery of small solutes was hardly affected by the applied pumping methods; however the relative recovery of macromolecules was significantly influenced by them. The in situ calibration technique using Phenol Red can provide reliable results for small molecules including glucose and lactic acid. Using lOkDa and 70kDa fluorescent dextrans as the internal standard for in situ calibration of large molecules of similar size, it was found that the pull pump system did not work well but that the push-and-pull pumping method did work well. A novel bioreactor system for in vitro IVD culture with static load and microdialysis monitoring was developed. Explanted IVDs were cultured under three different loads for up to 7 days. A single microdialysis probe with 3000 kDa membrane was inserted into each of the IVDs at a defined location. The in situ calibration technique was proved valid in the experiments and membrane fouling was not significant. The tissue metabolism and extracellular matrix turnover during 7 day culture were continuously monitored to investigate the effect of different loads. Microdialysis proved to be a feasible and efficient method for multi-parameter monitoring of tissue culture. Substantial effort was directed towards the identification of functional macromolecular markers in conjunction with microdialysis sampling. Amongst several proteins sampled, chitinase-3-like protein 1 (CHI3L1), a major soluble protein secreted by cultured IVD cells in alginate beads and by cultured IVD explants was identified following its successful isolation. Then it was established as a suitable functional marker. The effect of physico-chemical and mechanical stimuli (e.g. osmolarity, pH, oxygen tension and mechanical load) on secretion of CHI3L1 by cultured IVD cells and chondrocytes in alginate beads and by cultured IVD explant were investigated. CHI3L1 release was sensitive to physico-chemical stimulation. The production of CHI3L1 was directly correlated with the cell metabolism and this could be readily monitored with microdialysis.

Styles APA, Harvard, Vancouver, ISO, etc.

44

Eifert, Joseph D. « Predictive modeling of the aerobic growth of Staphylococcus aureus 196E using a nonlinear model and response surface analysis ». Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/27970.

Texte intégral

Résumé :

Pathogenic bacteria in foods are affected by several factors which may interact to enhance or inhibit microbial growth. Staphylococcus aureus 196E was inoculated into Brain Heart Infusion broth formulated with either 0.5, 4.5 or 8.5% NaCI, adjusted to pH 5.0, 6.0 or 7.0, and incubated aerobically at 12, 20 or 28°C. Mathematical models to predict the growth of S. aureus 196E were developed using a modified Gompertz function and response surface methodology. Each predictive equation required the estimation of only 23 parameters with a biological meaning. These models determined the significance of time, incubation temperature, sodium chloride (NaCI) concentration, and either pH or the logₑ of the undissociated acid concentration and any interactions on growth kinetics. Separate models were developed for the cases where pH was altered with either acetic acid, acetic acid plus sodium hydroxide, lactic acid and hydrochloric acid. All models adequately predicted the log growth of S. aureus 196E. Several interactive relationships between the independent variables upon population growth were significant. Predicted responses to multiple factor interactions were displayed with three-dimensional and contour plots. One model developed from a smaller subset of the growth data demonstrated that models could be produced with much less data collection. Generally, predictions of growth showed that acetic acid was more inhibitory to growth than lactic and hydrochloric acids. Furthermore, predicted and observed growth was slower or reduced when the undissociated acetic acid concentration was elevated at a specific pH. This methodology can provide important information to food scientists about the growth kinetics of microorganisms and prediction ranges or confidence intervals for growth parameters. Consequently, the effects of food formulations and storage conditions on the growth kinetics of foodborne pathogens or spoilage microorganisms could be predicted.
Ph. D.

Styles APA, Harvard, Vancouver, ISO, etc.

45

Guha, Roy Aimee. « Microalgal growth and lipid production : trends, multiple regression models, and validation in a photobioreactor ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:282874c9-06d4-41bf-bdc9-fb4ff515f57c.

Texte intégral

Résumé :

Algae are a promising new source of oil for biodiesel. They are aquatic organisms that do not require cropland, and they can produce many useful side-products for bioenergy, aquaculture, and nutraceutical production. To be cost-effective, algae need high and reliable oil productivities; however, there is still a great deal to learn about the effects of culturing conditions on algae growth rates and lipid production. These culturing conditions include light intensity, gas flow, use of CO₂, and culture volume. An extensive database of published research on algae growth rates and lipid contents under a wide variety of environmental conditions was prepared. By graphing data from 116 publications on 132 microalgae species, several key trends were identified relating to culturing parameters and algae biomass and lipid production. In addition, data from 131 publications on 128 microalgae species were graphed to look at presence of flagella, nutrient limitation, lipid productivity, and productivity tradeoffs. Moreover, cell size information was gathered for 146 species. The interactions between culture variables are complex, so it is difficult to quantify the degree to which each culture variable affects algae growth rates and lipid production. Therefore, several multivariate analyses were performed to generate a set of general and simple predictive models to assess specific growth rates, maximum lipid contents, and volumetric lipid productivities. These models were used to determine which culture parameters were significant predictors of algae growth rates and lipid production, and the contribution of each environmental parameter was quantified. In addition to models for algae in general, genera specific models were prepared for Chlorella, Isochrysis, Nannochloropsis, Phaeodactylum, and Tetraselmis. These models show high predictive capabilities, and they greatly extend the range of species-specific multiple regression models available. Furthermore, one Tetraselmis model was validated using Tetraselmis impellucida growth experiments in a large novel photobioreactor.

Styles APA, Harvard, Vancouver, ISO, etc.

46

Ni, Xinyu. « What Influences School District Effectiveness Growth Trajectories ? A Growth Mixture Modeling (GMM) Analysis ». Thesis, Teachers College, Columbia University, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=13805575.

Texte intégral

Résumé :

As a local education agency, school districts play an important role in providing instructional support for teachers and school leaders, making instructional goals, and allocating financial and human capital resources in a rational way to promote overall students’ learning outcomes. Studies on school districts that look to find reasons or characteristics related to school district success are known as district effectiveness research (DER). Previous quantitative research in DER using longitudinal dataset has assumed that all school district effectiveness (SDE) changes in a common pattern through a traditional ordinary linear regression or a hierarchal linear model while ignoring the probability that there might exist distinct subgroups of school district effectiveness trajectories. Thus, the purpose of the present study was to examine the existence of different SDE trajectories and how school district demographic variables and financial expenditures affect classification of SDE groups using a growth mixture model (GMM) with a national longitudinal dataset containing all public school districts in all 50 states and Washington D.C. from 2009 to 2015 (n = 11,185). The results indicated that (a) there are three different classes of school district effectiveness growth trajectories, which can be named as a constant SDE group (3.66%), a decreasing SDE group (34.16%), and an increasing SDE group (62.18%); (b) school district demographic characteristics such as a percentage of free lunch students and general administration expenditure per pupil are significantly associated with the probability of a school district being classified to a specific group; and (c) the longitudinal effects of school district demographic covariates and financial expenditures within each class such as school district locations (e.g., urban, suburban, etc.) are associated with the growth factors (intercept and slopes) in different ways.

Styles APA, Harvard, Vancouver, ISO, etc.

47

Nilsson, Karin. « Intracellular regulation in bacteria : control of initiation of chromosome replication ; macrolide antibiotics, resistance mechanisms and bi-stable growth rates / ». Uppsala : Dept. of Biometry and Engineering, Swedish University of Agricultural Sciences, 2006. http://epsilon.slu.se/200672.pdf.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

48

Lindner, Gerard Eckard. « Development of potential height growth and diameter increment models for the parameterisation of an individual tree growth model for Pinus elliottii plantations in South Africa ». Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86621.

Texte intégral

Résumé :

Thesis (MScFor)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Individual tree models, as opposed to stand models, have the potential to greatly improve sensitivity of forest growth models to changing conditions such as silvicultural amendments, irregular stand structures, etc. It was the purpose of this study to extend two sub-components of a European individual tree growth model to introduce individual tree growth modelling concepts in South Africa using Pinus elliottii as a study species. Two main objectives were established: Modelling the potential height of stands across different site qualities and modelling diameter increment using a potential modifier approach with a combination of competition indices that change in importance according to the edaphic conditions of the site. Potential height modelling used three steps in order to achieve this objective. The first was to compare site index models based on different model fitting techniques, namely nonlinear least squares, generalised nonlinear least squares and nonlinear mixed effects models. The nonlinear mixed effects model proved to be superior in terms of achieving the principles of regression assumptions and model fit for the data range observed. The second step was to fit potential height using nonlinear quantile regression on observed spacing trial height measurements. This proved to be a robust technique able to capture potentials according to the defined Chapman-Richards model structure. The final step was to use the predicted site index as a site classification variable in order to predict potential height. While some small deviation occurred, potential height seems to be well correlated to site index and validation on selected sites suggested that site index can be used to model potential height until a more sophisticated site classification model is used for future improvement of the model. Diameter increment modelling followed six major steps in order to apply the full parameterisation methodology of an age-independent diameter increment model dependent on tree diameter and competition. Diameter increment potentials were fit using site index as a predictor of the potential height curves. Multiple competition indices were tested on two sites to obtain a combination of two indices, which can capture overtopping and local crowding effects. Principle components analysis and variance inflation factors calculation were applied to test for collinearity between indices. Suitable combinations were tested resulting in a combination of the KKL and Local Basal Area competition indices. Changing importance of the two indices were observed on the two sites tested indicating a shift in the mode of competition according to a water gradient. These were combined in a deterministic potential modifier model, which mimicked competitive stages over age; however the validation showed a skewed distribution, which was not sensitive to stand density gradients. A stochastic model was constructed to model variance from observed residual plots using linear quantile regression to determine bounds for a truncated normal distribution which generates random deviates for a predicted increment. The stochastic element significantly improved the performance and sensitivity of the model, however the model was still not sensitive enough at very high and very low spacing densities. All in all two key models for an adaptation of an individual tree growth simulator to South African conditions were successfully demonstrated. The two main objectives were achieved; however some indicated improvements could be made, especially for the competition indices where the sensitivity of competition to changing resource limitation according to site and temporal scales needs to be further investigated. Furthermore, the full set of models for simulating individual tree growth still needs to be applied. Overall, as a methodological approach, the study outlined problems and future improvements, introduced new concepts and can serve as a guideline for future parameterisation of an individual tree growth model.
AFRIKAANSE OPSOMMING: In vergelyking met vakgroeimodelle, het individuele-boomgroeimodelle die potensiaal om die sensitiwiteit van plantasiegroeimodelle vir veranderende omstandighede soos aanpassings in boskultuur, onreëlmatige vakstrukture, ensovoorts, drasties te verbeter. Die doel van hierdie studie was om twee subkomponente van ‘n Europese individuele-boomgroeimodel uit te brei om sodoende individuele-boomgroei modelleringskonsepte in Suid-Afrika bekend te stel. Pinus elliottii is gebruik as studiespesie. Twee hoofdoelstellings is bepaal. Eerstens, die modellering van hoogtegroei potensiaal van opstande oor verskeie vlakke van groeiplek kwaliteit. Tweedens, die modellering van deursnee-aanwas deur gebruik te maak van ‘n potensiaal matigingsbenadering “potential modifier approach“ met ‘n kombinasie van kompetisie-indekse waarvan die belangrikheid verander volgens die edafiese toestande van die groeiplek. Die hoogtepotensiaalmodellering bestaan uit drie stappe. Tydens die eerste stap word groeiplek bonniteitsmodelle vergelyk op grond van verskillende modelpassingstegnieke, naamlik nie-lineêre minimum kwadrate, algemene nie-lineêre minimum kwadrate en nie-lineêre gemengde effek modelle. Laasgenoemde het die beste gevaar in terme van die beginsels van regressiemodelle asook die mate waarin die model die waargeneemde data pas. Tweedens is hoogtegroei potensiaal gemodelleer deur nie-lineêre kwantielregressie op waargeneemde hoogtes van spasiëringseksperimente toe te pas. Die metode is robuust en in staat om potensiale volgens die gedefinieerde Chapman Richards modelstruktuur vas te vang. Laastens is die voorspelde bonniteits indeks as ‘n groeiplek klassifasie veranderlike gebruik om sodoende die hoogtegroei potensiaal te voorspel. Alhoewel klein afwykings voorgekom het, blyk hoogtegroei potensiaal goed gekorreleer te wees met bonniteits indeks. Uit validasie op geselekteerde groieplekke blyk dit dat bonniteits indeks gebruik kan word om hoogtegroei potensiaal te modelleer totdat ‘n meer gesofistikeerde groeiplek klassifikasiemodel beskikbaar is wat die model verder sal kan vebeter. Die volledige parametriseringsmetodiek van ‘n ouderdoms-onafhanklike deursnee-aanwas model wat afhanklik is van boomdeursnee en kompetisie bestaan uit ses hoof prosesse. Nie-lineêre kwantielregressie is gebruik om deursnee-aanwaspotensiale te pas vir verskeie groeiplekke. Dié is gekombineer met ‘n bonniteits indeks om ‘n nuwe model te vorm waarmee hoogtegroeipotensiaal kurwes voorpel kon word. Daar is met veelvuldige kompetisie-indekse op twee groeiplekke geëksperimenteer om ‘n kombinasie van slegs twee indekse te vind wat die effekte van oorskaduwing en plaaslike verdringing kan vasvang, te vind. Hoof komponent analise “Principle components analysis” en variansie inflasie faktore berekening “variance inflation factors calculation” is gebruik om vir kollineariteit tussen die indekse te toets. Gepaste indekskombinasies is getoets. ‘n Kombinasie van die KKL en plaaslike basale oppervlakte “Local Basal Area” kompetisie-indekse het die beste resultate gelewer. Die twee indekse is as volg geselekteer. Veranderings in die belangrikheid van elk van die indekse is waargeneem op die twee toetspersele. Dit dui op ‘n verskuiwing in die modus van kompetisie afhangend van ‘n watergradiënt. Die twee indekse is gekombineer in ‘n deterministiese potensiaal matigings model wat die kompeterende stadiums oor ouderdom naboots. Validasie het egter ‘n skewe verdeling wat nie sensitief vir opstandsdigtheidsgradiënte is nie, gewys. ‘n Stogastiese model is ontwikkel om variansie in die residuele grafieke te modelleer. Lineêre kwantielregressie is gebruik om grense vir ‘n afgestompte normaalverdeling wat ewekansige afwykings vir ‘n voorspelde aanwas te bepaal. Die stogastiese element het die prestasie van die deterministiese model merkbaar verbeter. Selfs met die stogastiese element, is die model egter steeds nie sensitief genoeg vir baie hoë en baie lae opstandsdigthede nie. Ter opsomming is twee modelle vir ‘n aanpassing van ‘n individuele-boomgroeisimuleerder vir Suid- Afrikaanse toestande suksesvol gedemonstreer. Die twee hoofdoelstellings is bereik. Daar is egter steeds ‘n paar aangeduide verbeterings wat aangebring kan word. Die sensitiwiteit van die kompetisie-indekse op hulpbronbeperkings wat verander op grond van die ruimtelike en temporale skale moet veral verder bestudeer word. Verder moet die volle stel modelle wat benodig word om individuele-boomgroei te modelleer nog toegepas word. As ‘n metodologiese benadering, het die studie probleme uitgewys en toekomstige verbeterings aangedui, nuwe konsepte bekendgestel en kan dus dien as ‘n riglyn vir toekomstige parametrisering van individuele-boomgroeimodelle.

Styles APA, Harvard, Vancouver, ISO, etc.

49

GABLER, Alain. « On the macroeconomics of firm entry and exit ». Doctoral thesis, 2007. http://hdl.handle.net/1814/10690.

Texte intégral

Résumé :

Defence date: 23 November 2007
Examining Board: Prof. Omar Licandro, (EUI) ; Prof. Salvador Ortigueira, (EUI) ; Prof. Fabrizio Zilibotti, (University of Zurich) ; Prof. Hugo Hopenhayn, (UCLA)
PDF of thesis uploaded from the Library digital archive of EUI PhD theses
This thesis straddles two seemingly quite distinct fields within macroeconomics, namely endogenous growth and business cycle theory. The unifying element of the thesis is the fundamental role played by firm entry and exit in each chapter. In the longrun, I find that if entering firms imitate incumbents, firm turnover promotes growth by removing inefficient firms and replacing them by more productive ones. In the shortrun, fluctuations in the number of firms lead to movements in sectoral relative prices. In particular, pro-cyclical net entry leads to a fall in the price of investment in terms of consumption goods during booms; those relative price movements may be delayed if it takes time to set up a firm. The first chapter deals with the long-run effects of firm turnover. I set up a dynamic general equilibrium model with firm-specific productivity shocks. Those firms whose productivity has fallen too low exit, and entrants’ expected productivity is a function of current average productivity. Because of the resulting selection and imitation process (similar in some ways to the concept of natural selection), aggregate productivity in the economy grows endogenously. When calibrated to U.S. data, the model suggests that around one-fifth of productivity growth is due to such a selection effect. The following two chapters deal with the short-run effects of net firm entry within a framework of imperfect competition. I argue that the counter-cyclical fluctuations in the price of investment in terms of consumption goods which are observed for the U.S. are due to pro-cyclical competitive pressure through variations in the number of firms. The idea is that, since investment is much more variable than consumption, competition will be more variable in the investment sector, thereby pushing down prices more strongly in the latter sector during expansions.

Styles APA, Harvard, Vancouver, ISO, etc.

50

« Persistence and reversal of capital structure : evidence from Asia ». 2008. http://library.cuhk.edu.hk/record=b5893646.

Texte intégral

Résumé :

Law, Tak Yan.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2008.
Includes bibliographical references (leaves 38-39).
Abstracts in English and Chinese.
Chapter Chapter 1. --- Introduction --- p.1
Chapter Chapter 2. --- Literature Review --- p.4
Chapter 2.1 --- Brief Overview --- p.4
Chapter 2.2 --- Determinants of the Target Debt Ratio --- p.7
Chapter 2.3 --- Adjustments Toward the Target Ratio --- p.9
Chapter Chapter 3. --- Methodology --- p.12
Chapter 3.1 --- Estimation of the Target Leverage Ratio --- p.12
Chapter 3.2 --- Factors affecting the Long-term Adjustment --- p.16
Chapter 3.3 --- Persistence and Reversal of Effects --- p.19
Chapter Chapter 4. --- Expected Signs of Variables --- p.22
Chapter 4.1 --- Estimation of the Target Ratio --- p.22
Chapter 4.2 --- Effects of Firm Histories --- p.24
Chapter 4.2.1 --- Pecking order theory --- p.24
Chapter 4.2.2 --- Tradeoff theory --- p.25
Chapter 4.2.3 --- Market Timing Theory --- p.25
Chapter Chapter 5. --- Data --- p.27
Chapter Chapter 6. --- Empirical Findings --- p.29
Chapter 6.1 --- Estimation of the Target Ratio --- p.29
Chapter 6.2 --- Factors Affecting the Long-term Adjustment --- p.31
Chapter 6.3 --- Persistence of the Effects --- p.33
Chapter 6.4 --- Reversal of the Effects --- p.35
Chapter Chapter 7. --- Concluding Remarks --- p.37
References --- p.38
Tables --- p.40

Styles APA, Harvard, Vancouver, ISO, etc.

Thèses sur le sujet « Corporations – Growth – Mathematical models »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres