967 resultados para Models, Theoretical
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This study examines the effect of blood absorption on the endogenous fluorescence signal intensity of biological tissues. Experimental studies were conducted to identify these effects. To register the fluorescence intensity, the fluorescence spectroscopy method was employed. The intensity of the blood flow was measured by laser Doppler flowmetry. We proposed one possible implementation of the Monte Carlo method for the theoretical analysis of the effect of blood on the fluorescence signals. The simulation is constructed as a four-layer skin optical model based on the known optical parameters of the skin with different levels of blood supply. With the help of the simulation, we demonstrate how the level of blood supply can affect the appearance of the fluorescence spectra. In addition, to describe the properties of biological tissue, which may affect the fluorescence spectra, we turned to the method of diffuse reflectance spectroscopy (DRS). Using the spectral data provided by the DRS, the tissue attenuation effect can be extracted and used to correct the fluorescence spectra.
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A tanulmny a PPP klnbz strukturlis modelljeinek csoportostst mutatja be, az egyes tpusok rvid rendszerez ttekintsvel. A tipolgik vizsglata hasznos ahhoz, hogy a PPP projektek struktrjnak kialaktsakor a klnbz lehetsgeket mrlegelni tudjuk. Tbbfle megkzeltsben lehet a modelleket tipizlni. Az egyttmkds clja alapjn a hatkonysg-, a minsg- s a finanszrozs-orientlt modellek a legelterjedtebbek, a kockzatmegoszts mdja alapjn BOT, DBFO s koncesszis vltozatok, a haszonmegoszts szablyozsa alapjn rplafon-szablyozs, kzvetlen haszonszablyozs, fixdjas s rnykras megoldsok a leginkbb bevettek. A tanulmny ezek elemz bemutatsa alapjn arra a kvetkeztetsre jut, hogy a gyakorlati megoldsok a legtbb esetben az elmleti tpusok valamilyen kombincijt tartalmazzk, a konkrt eset feltteleinek megfelelen. gy a gyakorlatban a fix tipolgik helyett alkalmasabb gy megkzeltennk a PPP-t, mint egy folyamatosan vltoz, a helyi ignyekhez idomul jelensget. A haszonszablyoz tipolgia kapcsn a tanulmny mellklete rvid ttekintst nyjt a PPP esetben kritikus mltnyos haszon becslsnek lehetsges megoldsairl is. = This study shows a categorization of the different structural models of Public-Private Partnership (PPP) projects. The typologies are useful to assess the available options when decisions on PPP project structures are made. There are different categorizing aspects. Based ont he key purpose of the partnership there are efficiency, quality and financing focused models. From a risk sharing point of view, BOT, DBFO and concession models are most typical. Regarding the regulation of returns price-cap models, open book models, fixed price and shadow pricing models are most common. Based on the analytical assessment of these, they study concludes that actual projects are mostly a combination of theoretical types, as required by the given case. Therefore in practice, it is more appropriate to approach PPP projects as a constantly shaping concept, adjustable to particular conditions. Supporting the approaches to the regulation of returns, an appendix of the study summarizes the different methods to estimate fair returns, a critical issue in PPP projects.
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A svosan rgztett devizarfolyamok elmleti s gyakorlati vizsglatai a nemzetkzi kzgazdasgtan egyik legnpszerbb tmakre volt a kilencvenes vek elejn. A gyakorlati mdszerek kzl az alkalmazsok s hivatkozsok szma tekintetben az gynevezett eltoldssal igazts mdszere emelkedett ki. A mdszert alkalmaz szerzk szerint amg a lebeg rfolyam devizk elrejelzse cltalan feladatnak tnik, addig svos rfolyam esetn az rfolyam svon belli helyzetnek elrejelzse sikeresen vgezhet. E tanulmny bemutatja, hogy az Eurpai Monetris Rendszer s az szakeurpai llamok svos rfolyamrendszereinl e mdszer alkalmazsval addott eredmnyek pldul a lebeg rfolyam amerikai dollrra s az egysggykfolyamatok tbbsgre is rvnyesek. A tanulmny feltrja e ltszlagos ellentmonds okait, s bemutat egy olyan, a svos rfolyamrendszerek fbb megfigyelt jellemzire pl modellt, amelynek keretei kztt a svon belli rfolyam elrejelzse nem felttlenl lehetsges, mert a lertkels eltti idszakban a svon belli rfolyam alakulsa kaotikus lehet. / === / Following the development of the first exchange rate target zone model at the end of the eighties dozens of papers analyzed theoretical and empirical topics of currency bands. This paper reviews different empirical methods to analyze the credibility of the band and lays special emphasis on the most widely used method, the so-called drift-adjustment method. Papers applying that method claim that while forecasting a freely floating currency is hopeless, predicting an exchange rate within the future band is successful. This paper shows that the results achieved by applications to EMS and Nordic currencies are not specific to data of target zone currencies. For example, application to US dollar and even to most unit root processes leads qualitatively to the same. This paper explores the solutions of this puzzle and shows a model of target zones in which the exchange rate within the band is not necessarily predictable since the process might follow chaotic dynamics before devaluation.
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A szerz az alkalmazott tbbszektoros modellezs terletn a lineris programozsi modellektl a szmszerstett ltalnos egyenslyi modellekig vgbement vltozsokat tekinti t. Egy rvid trtneti visszapillants utn a lineris programozs mdszereire pl nemzetgazdasgi szint modellekkel sszevetve mutatja be az ltalnos egyenslyi modellek kzs, illetve eltr jellemzit. Egyidejleg azt is rzkelteti, hogyan lehet az ltalnos egyenslyi modelleket a gazdasgpolitikai clok konzisztencijnak, a clok kztti tvltsi lehetsgek elemzsre s ltalban a gazdasgpolitikai elkpzelsek rzkenysgi vizsglatra felhasznlni. A szerz az elmleti-mdszertani krdsek taglalst szmszerstett ltalnos egyenslyi modell segtsgvel illusztrlja. _______ The author surveys the changes having taken place in the field of multi-sector modeling, from the linear programming models to the quantified general equilibrium models. After a brief historical retrospection he presents the common and different characteristic features of the general equilibrium models by comparing them with the national economic level models based on the methods of linear programming. He also makes clear how the general equilibrium models can be used for analysing the consistency of economic policy targets, for the investigation of trade-off possibilities among the targets and, in general, for sensitivity analyses of economic policy targets. The discussion of theoretical and methodological quuestions is illustrated by the author with the aid of a quantified general equilibrium model.
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Climate change has a great impact on the build and the work of natural ecosystems. Disappearance of some population or growth of the number in some species can be already caused by little change in temperature. A Theoretical Ecosystem Growth Model was investigated in order to examine the effects of various climate patterns on the ecological equilibrium. The answers of the ecosystems which are given to the climate change could be described by means of global climate modelling and dynamic vegetation models. The examination of the operation of the ecosystems is only possible in huge centres on supercomputers because of the number and the complexity of the calculation. The number of the calculation could be decreased to the level of a PC by considering the temperature and the reproduction during the modelling of a theoretical ecosystem and several important theoretical questions could be answered.
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A szerz a tisztn elmleti clokra kifejlesztett Neumann-modellt s a gyakorlati alkalmazsok cljra kifejlesztett Leontief-modellt veti ssze. A Neumann-modell s a Leontief-modell ves termelsi peridust felttelez, zrt, stacionrius vltozatnak hasonl matematikai struktrja azt a felttelezst sugallja, hogy az utbbi a Neumann-modell sajtos eseteknt rtelmezhet. Az egyes modellek kzgazdasgi tartalmt s feltevseit rszletesen kibontva s egymssal sszevetve a szerz megmutatja, hogy a fenti kvetkeztets flrevezet, kt merben klnbz modellrl van sz, nem lehet az egyikbl a msikat levezetni. Az ikertermels s technolgiai vlasztk lehetsge a Neumann-modell elengedhetetlen feltevse, az ves termelsi peridus feltevse pedig kizrja folyam jelleg kibocstsok explicit figyelembevtelt. Mindezek feltevsek ugyanakkor idegenek a Leontief-modelltl. A kt modell valjban egy ltalnosabb llomnyfolyam jelleg zrt, stacionrius modell sajtos esete, mghozz azok folyamvltozkra reduklt alakja. _____ The paper compares the basic assumptions and methodology of the Von Neumann model, developed for purely abstract theoretical purposes, and those of the Leontief model, designed originally for practical applications. Study of the similar mathematical structures of the Von Neumann model and the closed, stationary Leontief model, with a unit length of production period, often leads to the false conclusion that the latter is just a simplified version of the former. It is argued that the economic assumptions of the two models are quite different, which makes such an assertion unfounded. Technical choice and joint production are indispensable features of the Von Neumann model, and the assumption of unitary length of production period excludes the possibility of taking service flows explicitly into account. All these features are completely alien to the Leontief model, however. It is shown that the two models are in fact special cases of a more general stock-flow stationary model, reduced to forms containing only flow variables.
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The contractile state of microcirculatory vessels is a major determinant of the blood pressure of the whole systemic circulation. Continuous bi-directional communication exists between the endothelial cells (ECs) and smooth muscle cells (SMCs) that regulates calcium (Ca2+) dynamics in these cells. This study presents theoretical approaches to understand some of the important and currently unresolved microcirculatory phenomena. ^ Agonist induced events at local sites have been shown to spread long distances in the microcirculation. We have developed a multicellular computational model by integrating detailed single EC and SMC models with gap junction and nitric oxide (NO) coupling to understand the mechanisms behind this effect. Simulations suggest that spreading vasodilation mainly occurs through Ca 2+ independent passive conduction of hyperpolarization in RMAs. Model predicts a superior role for intercellular diffusion of inositol (1,4,5)-trisphosphate (IP3) than Ca2+ in modulating the spreading response. ^ Endothelial derived signals are initiated even during vasoconstriction of stimulated SMCs by the movement of Ca2+ and/or IP3 into the EC which provide hyperpolarizing feedback to SMCs to counter the ongoing constriction. Myoendothelial projections (MPs) present in the ECs have been recently proposed to play a role in myoendothelial feedback. We have developed two models using compartmental and 2D finite element methods to examine the role of these MPs by adding a sub compartment in the EC to simulate MP with localization of intermediate conductance calcium activated potassium channels (IKCa) and IP3 receptors (IP 3R). Both models predicted IP3 mediated high Ca2+ gradients in the MP after SMC stimulation with limited global spread. This Ca 2+ transient generated a hyperpolarizing feedback of 23mV. ^ Endothelium derived hyperpolarizing factor (EDHF) is the dominant form of endothelial control of SMC constriction in the microcirculation. A number of factors have been proposed for the role of EDHF but no single pathway is agreed upon. We have examined the potential of myoendothelial gap junctions (MEGJs) and potassium (K+) accumulation as EDHF using two models (compartmental and 2D finite element). An extra compartment is added in SMC to simulate micro domains (MD) which have NaK2 isoform sodium potassium pumps. Simulations predict that MEGJ coupling is much stronger in producing EDHF than alone K+ accumulation. On the contrary, K+ accumulation can alter other important parameters (EC V m, IKCa current) and inhibit its own release as well as EDHF conduction via MEGJs. The models developed in this study are essential building blocks for future models and provide important insights to the current understanding of myoendothelial feedback and EDHF.^
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Microcirculatory vessels are lined by endothelial cells (ECs) which are surrounded by a single or multiple layer of smooth muscle cells (SMCs). Spontaneous and agonist induced spatiotemporal calcium (Ca2+) events are generated in ECs and SMCs, and regulated by complex bi-directional signaling between the two layers which ultimately determines the vessel tone. The contractile state of microcirculatory vessels is an important factor in the determination of vascular resistance, blood flow and blood pressure. This dissertation presents theoretical insights into some of the important and currently unresolved phenomena in microvascular tone regulation. Compartmental and continuum models of isolated EC and SMC, coupled EC-SMC and a multi-cellular vessel segment with deterministic and stochastic descriptions of the cellular components were developed, and the intra- and inter-cellular spatiotemporal Ca2+ mobilization was examined. Coupled EC-SMC model simulations captured the experimentally observed localized subcellular EC Ca2+ events arising from the opening of EC transient receptor vanilloid 4 (TRPV4) channels and inositol triphosphate receptors (IP3Rs). These localized EC Ca2+ events result in endothelium-derived hyperpolarization (EDH) and Nitric Oxide (NO) production which transmit to the adjacent SMCs to ultimately result in vasodilation. The model examined the effect of heterogeneous distribution of cellular components and channel gating kinetics in determination of the amplitude and spread of the Ca2+ events. The simulations suggested the necessity of co-localization of certain cellular components for modulation of EDH and NO responses. Isolated EC and SMC models captured intracellular Ca2+ wave like activity and predicted the necessity of non-uniform distribution of cellular components for the generation of Ca2+ waves. The simulations also suggested the role of membrane potential dynamics in regulating Ca2+ wave velocity. The multi-cellular vessel segment model examined the underlying mechanisms for the intercellular synchronization of spontaneous oscillatory Ca2+ waves in individual SMC. From local subcellular events to integrated macro-scale behavior at the vessel level, the developed multi-scale models captured basic features of vascular Ca2+ signaling and provide insights for their physiological relevance. The models provide a theoretical framework for assisting investigations on the regulation of vascular tone in health and disease.
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This chapter sets out a comprehensive analysis of the regulation of money market funds in the EU and US. The theoretical framework has unique cases and examples and includes checklists to assist with the practice of fund management and legal risk analysis.
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Literature describing the notion and practice of business models has grown considerably over the last few years. Innovative business models appear in every sector of the economy challenging traditional ways of creating and capturing value. However, research describing the theoretical foundations of the field is scarce and many questions still remain. This article examines business models promoting various aspects of sustainable development and tests the explanatory power of two theoretical approaches, namely the resource based view of the firm and transaction cost theory regarding their emergence and successful market performance. Through the examples of industrial ecology and the sharing economy the author shows that a sharp reduction of transaction costs (e.g. in the form of internet based systems) coupled with resources widely available but not utilised before may result in fast growing new markets. This research also provides evidence regarding the notion that these two theoretical approaches can complement each other in explaining corporate behaviour.
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Thesis (Ph.D.)--University of Washington, 2016-08
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In the recent years, vibration-based structural damage identification has been subject of significant research in structural engineering. The basic idea of vibration-based methods is that damage induces mechanical properties changes that cause anomalies in the dynamic response of the structure, which measures allow to localize damage and its extension. Vibration measured data, such as frequencies and mode shapes, can be used in the Finite Element Model Updating in order to adjust structural parameters sensible at damage (e.g. Youngs Modulus). The novel aspect of this thesis is the introduction into the objective function of accurate measures of strains mode shapes, evaluated through FBG sensors. After a review of the relevant literature, the case of study, i.e. an irregular prestressed concrete beam destined for roofing of industrial structures, will be presented. The mathematical model was built through FE models, studying static and dynamic behaviour of the element. Another analytical model was developed, based on the Ritz method, in order to investigate the possible interaction between the RC beam and the steel supporting table used for testing. Experimental data, recorded through the contemporary use of different measurement techniques (optical fibers, accelerometers, LVDTs) were compared whit theoretical data, allowing to detect the best model, for which have been outlined the settings for the updating procedure.
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Abstract: The importance of e-government models lies in their offering a basis to measure and guide e-government. There is still no agreement on how to assess a government online. Most of the e-government models are not based on research, nor are they validated. In most countries, e-government has not reached higher stages of growth. Several scholars have shown a confusing picture of e-government. What is lacking is an in-depth analysis of e-government models. Responding to the need for such an analysis, this study identifies the strengths and weaknesses of major national and local e-government evaluation models. The common limitations of most models are focusing on the government and not the citizen, missing qualitative measures, constructing the e-equivalent of a bureaucratic administration, and defining general criteria without sufficient validations. In addition, this study has found that the metrics defined for national e-government are not suitable for municipalities, and most of the existing studies have focused on national e-governments even though local ones are closer to citizens. There is a need for developing a good theoretical model for both national and local municipal e-government.
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This paper provides an exploratory study of how rewards-based crowdfunding affects business model development for music industry artists, labels and live sector companies. The empirical methodology incorporated a qualitative, semi-structured, three-stage interview design with fifty seven senior executives from industry crowdfunding platforms and three stakeholder groups. The results and analysis cover new research ground and provide conceptual models to develop theoretical foundations for further research in this field. The findings indicate that the financial model benefits of crowdfunding for independent artists are dependent on fan base demographic variables relating to age group and genre due to sustained apprehension from younger audiences. Furthermore, major labels are now considering a more user-centric financial model as an innovation strategy, and the impact of crowdfunding on their marketing model may already be initiating its development in terms of creativity, strength and artist relations.
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BACKGROUND: Regional differences in physician supply can be found in many health care systems, regardless of their organizational and financial structure. A theoretical model is developed for the physicians' decision on office allocation, covering demand-side factors and a consumption time function. METHODS: To test the propositions following the theoretical model, generalized linear models were estimated to explain differences in 412 German districts. Various factors found in the literature were included to control for physicians' regional preferences. RESULTS: Evidence in favor of the first three propositions of the theoretical model could be found. Specialists show a stronger association to higher populated districts than GPs. Although indicators for regional preferences are significantly correlated with physician density, their coefficients are not as high as population density. CONCLUSIONS: If regional disparities should be addressed by political actions, the focus should be to counteract those parameters representing physicians' preferences in over- and undersupplied regions.
