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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
111

A simulation/optimization system for modelling timber and old forest under stochastic fire disturbance

Conrod, Matthew 06 1900 (has links)
Stochastic wildfire disturbance contributes to uncertainty in forest management planning. In this study, a system composed of an optimizing forest estate model nested within a Monte Carlo simulation model of stand replacing fires is used to investigate the impact stochastic fire may have on the achievement of harvest level and old forest area targets. Two different variations of the modelling system are used to test the impact a buffer stock of timber will have on the probability of achieving these indicators targets. Preliminary results suggest that a reduced harvest level may increase the probability of indicator achievement. However, the immediate harvest level decrease necessary is high and there is still no assurance of target achievement. Further, from a net present value perspective, most scenarios examined showed a higher proft in the absence of a buffer stock. / Forest Biology and Management
112

Fehlerrechnung in Oekobilanzen

Straubing 20 December 2001 (has links) (PDF)
No description available.
113

Monte Carlo Studies of Charge Transport Below the Mobility Edge / Monte Carlo-studier av Laddningstransport under Mobilitetsgränsen

Jakobsson, Mattias January 2012 (has links)
Charge transport below the mobility edge, where the charge carriers are hopping between localized electronic states, is the dominant charge transport mechanism in a wide range of disordered materials. This type of incoherent charge transport is fundamentally different from the coherent charge transport in ordered crystalline materials. With the advent of organic electronics, where small organic molecules or polymers replace traditional inorganic semiconductors, the interest for this type of hopping charge transport has increased greatly. The work documented in this thesis has been dedicated to the understanding of this charge transport below the mobility edge. While analytical solutions exist for the transport coefficients in several simplified models of hopping charge transport, no analytical solutions yet exist that can describe these coefficients in most real systems. Due to this, Monte Carlo simulations, sometimes described as ideal experiments performed by computers, have been extensively used in this work. A particularly interesting organic system is deoxyribonucleic acid (DNA). Besides its overwhelming biological importance, DNA’s recognition and self-assembly properties have made it an interesting candidate as a molecular wire in the field of molecular electronics. In this work, it is shown that incoherent hopping and the Nobel prize-awarded Marcus theory can be used to describe the results of experimental studies on DNA. Furthermore, using this experimentally verified model, predictions of the bottlenecks in DNA conduction are made. The second part of this work concerns charge transport in conjugated polymers, the flagship of organic materials with respect to processability. It is shown that polaronic effects, accounted for by Marcus theory but not by the more commonly used Miller-Abrahams theory, can be very important for the charge transport process. A significant step is also taken in the modeling of the off-diagonal disorder in organic systems. By taking the geometry of the system from large-scale molecular dynamics simulations and calculating the electronic transfer integrals using Mulliken theory, the off-diagonal disorder is for the first time modeled directly from theory without the need for an assumed parametric random distribution.
114

Extreme Value Theory with an Application to Bank Failures through Contagion

Nikzad, Rashid 03 October 2011 (has links)
This study attempts to quantify the shocks to a banking network and analyze the transfer of shocks through the network. We consider two sources of shocks: external shocks due to market and macroeconomic factors which impact the entire banking system, and idiosyncratic shocks due to failure of a single bank. The external shocks will be estimated by using two methods: (i) non-parametric simulation of the time series of shocks that occurred to the banking system in the past, and (ii) using the extreme value theory (EVT) to model the tail part of the shocks. The external shocks we considered in this study are due to exchange rate and treasury bill rate volatility. Also, an ARMA/GARCH model is used to extract iid residuals for this purpose. In the next step, the probability of the failure of banks in the system is studied by using Monte Carlo simulation. We calibrate the model such that the network resembles the Canadian banking system.
115

Extreme Value Theory with an Application to Bank Failures through Contagion

Nikzad, Rashid 03 October 2011 (has links)
This study attempts to quantify the shocks to a banking network and analyze the transfer of shocks through the network. We consider two sources of shocks: external shocks due to market and macroeconomic factors which impact the entire banking system, and idiosyncratic shocks due to failure of a single bank. The external shocks will be estimated by using two methods: (i) non-parametric simulation of the time series of shocks that occurred to the banking system in the past, and (ii) using the extreme value theory (EVT) to model the tail part of the shocks. The external shocks we considered in this study are due to exchange rate and treasury bill rate volatility. Also, an ARMA/GARCH model is used to extract iid residuals for this purpose. In the next step, the probability of the failure of banks in the system is studied by using Monte Carlo simulation. We calibrate the model such that the network resembles the Canadian banking system.
116

MODELING OLEFIN POLYMERIZATION USING MONTE CARLO SIMULATION: DETAILED COMONOMER DISTRIBUTION

Al-Saleh, Mohammad January 2006 (has links)
In recent years there have been many efforts to develop and expand the ability of mathematical models capable of describing polymerization systems. Models can provide a key competitive advantage for the industry and research in terms of production and technology development. As new resins are continuously produced to meet the requirement of final applications and processability, it is imperative to pursue strong polymer characterization with special attention to detailed analysis of polymer microstructure. The microstructure of polyolefin is defined by its distribution of molecular weight, chemical composition, branching topology, and stereoregularity. <br /><br /> In this work, a Monte Carlo simulation model was developed to describe the polymerization mechanisms of olefin homopolymerization and copolymerization using single-site coordination catalyst. The mathematical model is meant to describe molecular weight and chemical composition distribution in copolymerization system. More specifically, this research work gives a detailed study of the molecular structure for ethylene- alfa-olefin copolymer. <br /><br /> The chemical and physical properties of copolymers are influenced not only by their average composition, but also by the monomer sequence distribution along the polymer chains. Predicting the molecular weight and comonomer distributions can lead to a better understanding of the possible morphology in solid stated because they are considered to be the main structural parameters that affect the crystallinity of polymeric materials. As a consequence, final physical properties such as the tensile properties of a copolymer could be controlled by the ratio of crystalline species in the polymer. <br /><br /> This work is considered to be a useful tool that enables us to understand and explore specific polymerization catalytic system. Being able to describe the short chain branching and the monomer sequence distribution as a function of chain length enables us to have a better control over semi-batch polymerization reactors.
117

MODELING OLEFIN POLYMERIZATION USING MONTE CARLO SIMULATION: DETAILED COMONOMER DISTRIBUTION

Al-Saleh, Mohammad January 2006 (has links)
In recent years there have been many efforts to develop and expand the ability of mathematical models capable of describing polymerization systems. Models can provide a key competitive advantage for the industry and research in terms of production and technology development. As new resins are continuously produced to meet the requirement of final applications and processability, it is imperative to pursue strong polymer characterization with special attention to detailed analysis of polymer microstructure. The microstructure of polyolefin is defined by its distribution of molecular weight, chemical composition, branching topology, and stereoregularity. <br /><br /> In this work, a Monte Carlo simulation model was developed to describe the polymerization mechanisms of olefin homopolymerization and copolymerization using single-site coordination catalyst. The mathematical model is meant to describe molecular weight and chemical composition distribution in copolymerization system. More specifically, this research work gives a detailed study of the molecular structure for ethylene- alfa-olefin copolymer. <br /><br /> The chemical and physical properties of copolymers are influenced not only by their average composition, but also by the monomer sequence distribution along the polymer chains. Predicting the molecular weight and comonomer distributions can lead to a better understanding of the possible morphology in solid stated because they are considered to be the main structural parameters that affect the crystallinity of polymeric materials. As a consequence, final physical properties such as the tensile properties of a copolymer could be controlled by the ratio of crystalline species in the polymer. <br /><br /> This work is considered to be a useful tool that enables us to understand and explore specific polymerization catalytic system. Being able to describe the short chain branching and the monomer sequence distribution as a function of chain length enables us to have a better control over semi-batch polymerization reactors.
118

The Price Difference Analysis For Convertible Bonds

Shih, Chun-hsiung 13 July 2004 (has links)
none
119

The study of phase transition of liquid crystal in a coupled XY model

Shih, Chia-Chi 22 June 2005 (has links)
Abstract In this study, we employed the Monte Carlo simulation method to investigate the q-state coupled XY model based on the Landau free energy of couple hexatic order and herringbone order proposed by Bruinsma and Aeppli. On two-dimensional triangular lattices simulation results reveal that the q-state coupled XY model will generate a q-state clock phase transition and a XY transition. The unique generated q-state clock phase transition and XY transition will couple in some coupling parameter domain. The novel coupled transitions behavior agree with the phase transition of some kinds of liquid crystal. For example, the three-state Potts phase transition generated by a 3-state coupled XY model and the Sm-A ¡÷Hex-B transition of free ¡V standing two layers liquid crystal are matched. Their heat capacity anomaly is similar and the heat capacity exponent is both closed to £\¡Ü0.3. We also investigated the system of coupled ferromagnetic order and antiferromagnetic order. Adapted the positive coupling parameter on the Hamiltonian of 3-state coupled XY model, the simulation results reveal that the system generate an antiferromagnetic three-state Potts transition. In some parameter domain the antiferromagnetic three-state Potts transition and XY transition are coupled, and become a novel transition. The novel transition may explain the Sm-A ¡÷Hex-B transition of some kinds of liquid crystal which lack herringbone order.
120

Ensemble Monte Carlo Modeling Of Quantum Well Infrared Photodetectors

Memis, Sema 01 March 2006 (has links) (PDF)
Quantum well infrared photodetectors (QWIPs) have recently emerged as a potential alternative to the conventional detectors utilizing low bandgap semiconductors for infrared applications. There has been a considerable amount of experimental and theoretical work towards a better understanding of QWIP operation, whereas there is a lack of knowledge on the underlying physics. This work provides a better understanding of QWIP operation and underlying physics through particle simulations using the ensemble Monte Carlo method. The simulator incorporates Gamma, L, and X valleys of conduction band as well as the size quantization in the quantum wells. In the course of this work, the dependence of QWIP performance on different device parameters is investigated for the optimization of the QWIP structure. The simulations on AlGaAs/GaAs QWIPs with the typical Al mole fraction of 0.3 have shown that the L valley of the conduction band plays an important role in the electron capture. A detailed investigation of the important scattering mechanisms indicates that the capture of the electrons through the L valley quantum well (L-QW) affects the device performance significantly when Gamma and L valley separation is small. The characteristics of electron capture have been further investigated by repeating the simulations on QWIPs for quantum well widths of 36 and 44 &Aring / . The results suggest that the gain in the shorter well width device is considerably higher, which is attributed to the much longer lifetime of the photoexcited electrons as a result of lower capture probability (pc) in the device. The effects of the L-QW height on the QWIP characteristics have also been studied by artificially increasing this height from 63 to 95 meV in Al0.3Ga0.7As/GaAs QWIPs. The increase in the L valley (L-QW) height resulted in higher pc and lower gain due to high rate of capturing of these electrons when Gamma and L valley separation is small.

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