Dissertations / Theses on the topic 'Dynamic property'

Thesis (M.S.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains x, 89 p. : ill. Vita. Includes abstract. Includes bibliographical references (p. 62-64).

The objective of this thesis is to develop and validate a computational framework based on mathematical models for the motion prediction and dynamic stability quantification of human walking, which can differentiate the dynamic stability of human walking with different mechanical properties of the leg. Firstly, a large measurement database of human walking motion was created. It contains walking measurement data of 8 subjects on 3 self-selected walking speeds, which 10 trials were recorded at each walking speed. The motion of whole-body centre of mass and the leg were calculated from the kinetic-kinematic measurement data. The fundamentals of leg property have been presented, and the parameters of leg property were extracted from the measurement data of human walking where the effects of walking speed and condition of foot-ground contact were investigated. Three different leg property definitions comprising linear axial elastic leg property, nonlinear axial elastic leg property and linear axial-tangential elastic leg property were used to extracted leg property parameters. The concept of posture-dependent leg property has been proposed, and the leg property parameters were extracted from the measurement data of human walking motion where the effects of walking speed and condition of foot-ground contact were also investigated. The compliant leg model with axial elastic property (CAE) was used for the dynamic stability analysis of human walking with linear and nonlinear axial elastic leg property. The compliant leg model with axial and tangential elastic property (CATE) was used for that with linear axial-tangential elastic leg property. The posture - dependent elastic leg model (PDE) was used for that with posture-dependent leg property. It was found that, with linear axial elastic leg property, the global stability of human walking improves with the bigger touchdown contact angle. The average leg property obtained from the measurement data of all participants allows the maximum global stability of human walking. With nonlinear axial elastic leg property, the global stability decreases with the stronger nonlinearity of leg stiffness. The incorporation of the tangential elasticity improves the global stability and shifts the stable walking velocity close to that of human walking at self-selected low speed (1.1-1.25 m/s).By the PDE model, the human walking motions were better predicted than by the CATE model. The effective range of walking prediction was enlarged to 1.12 – 1.8 m/s. However, represented by PDE model, only 1-2 walking steps can be achieved. In addition, the profiles of mechanical energies represented by the PDE model are different from that of the orbital stable walking represented by CATE model. Finally, the minimal requirements of the human walking measurements and the flexibility of simple walking models with deliberate leg property definitions allow the computational framework to be applicable in the dynamic stability analysis of the walking motion with a wide variety of mechanical property of the leg.

[EN] The present work examines the influence of the chemical structure of polymers on thermal, mechanical and dielectric behavior. The experimental techniques used for the purpose are differential scanning calorimetry, dynamo-mechanical analysis and dielectric spectroscopy. Additionally, in order to confirm the results obtained using the above methods, other techniques such as ray diffraction have also been employed. Chapters 1 and 2 contain the introduction and the objectives, respectively. Chapter 3 briefly describes the experimental techniques used. Chapter 4 contains the findings of the comparative analysis of the response to electrical noise fields for three poly(benzyl methacrylates) with different structures. The analysis was carried out under a wide range of frequencies and temperatures on three poly(benzyl methacrylates) containing two dimethoxy groups in positions 2,5-, 2,3- and 3,4-. The results show that the position of the dimethoxy groups on the aromatic ring has a significant effect on the molecular dynamics of poly(benzyl methacrylate). The spectra obtained were of high complexity and therefore, in order to perform a better analysis, numerical methods for time-frequency transformation including the use of parametric regularization techniques were used. We studied the effect of this structural change on the secondary relaxation processes and relaxation process , relating to the glass transition. We also analyzed the effect of the dimethoxy group position on the formation of nanodomains, in which the side chains are predominant, and on the conduction processes of the materials tested. In Chapter 5, the conductivity of rubbery liquids was studied by analyzing poly(2,3-dimethoxybenzyl methacrylate), which exhibits its own particular behavior. The chapter analyzes the principle of time-temperature superposition, employing different interrelated variables. Chapter 6 focuses on how the presence of crosslinking affects the molecular mobility of polymethacrylates containing aliphatic alcohol ether residues. In this case, the effect of crosslinking on the secondary and primary relaxation processes was analyzed. The creation of nanodomains in the side chains as a result of the presence of crosslinking was also studied.
[ES] En este trabajo se presenta un estudio de la influencia de la estructura química de los polímeros en su comportamiento térmico, mecánico y dieléctrico. Las técnicas experimentales empleadas para ello han sido la calorimetría diferencial de barrido, el análisis dinamo-mecánico y la espectroscopia dieléctrica. Adicionalmente, se han empleado otras técnicas como la difracción de rayos, con objeto de corroborar los resultados obtenidos por las primeras. En los Capítulos 1 y 2 se recoge la introducción y los objetivos, respectivamente. El Capítulo 3 presenta una breve descripción de las técnicas experimentales empleadas. En el Capítulo 4 se recogen los resultados obtenidos en el análisis comparativo de la respuesta a campos de perturbación eléctrica en un amplio rango de frecuencias y temperaturas para tres polimetacrilatos de bencilo con dos grupos dimetoxi en posiciones 2,5-, 2,3- y 3,4-. Los resultados obtenidos señalan el importante efecto de la posición de los grupos dimetoxi en el anillo aromático, sobre la dinámica molecular del polimetacrilato de bencilo. Los espectros obtenidos fueron muy complejos, por ello en orden a llevar a cabo un mejor análisis se emplearon métodos numéricos para la transformación tiempo-frecuencia que incluyeron el uso de técnicas de regularización paramétrica. Se ha estudiado el efecto que dicho cambio estructural ejerce tanto sobre los procesos de relajación secundaria como sobre el proceso de relajación α, relacionado con la transición vítrea. Así mismo, se ha analizado el efecto de la posición de los grupos dimetoxi en la formación de iii nanodominios en los que predominan las cadenas laterales, y su efecto en los procesos de conducción de los materiales analizados. En el Capítulo 5 se recoge el estudio de la conductividad de líquidos gomosos tomando como modelo el poli (metacrilato de 2,3-dimetoxibencilo), por su peculiar comportamiento. En este capítulo se ha realizado un análisis del principio de superposición tiempo-temperatura, empleando para ello diferentes variables relacionadas entre sí. En el Capítulo 6 se recoge el efecto de la presencia de entrecruzante en la movilidad molecular de polimetacrilatos que contienen residuos de éteres de alcoholes alifáticos. En este caso, se ha analizado el efecto de la presencia de entrecruzante tanto en los procesos de relajación secundarios, como en el proceso de relajación principal. También se llevó a cabo un análisis del efecto que la presencia de entrecruzante tiene sobre la creación de nanodominios gobernados por las cadenas laterales.
[CAT] En aquest treball es presenta un estudi de la influència de l'estructura química dels polímers en el seu comportament tèrmic, mecànic i dielèctric. Les tècniques experimentals utilitzades han sigut la calorimetria diferencial de rastreig, l'anàlisi dinamo-mecànic i l'espectroscòpia dielèctrica. Addicionalment, s'han empleat altres tècniques com la difracció de rajos X a fi de corroborar els resultats obtinguts per les primeres. En els Capítols 1 i 2 s'arreplega la introducció i els objectius, respectivament. Al Capítol 3 es presenta una breu descripció de les tècniques experimentals emprades. En el Capítol 4 es recull els resultats obtinguts en l'anàlisi comparativa de la resposta a camps de pertorbació elèctrica en un ampli rang de freqüències i temperatures de tres polimetacrilats de benzil amb dos grups metoxi en posicions 2,5-, 2,3- i 3,4-. Els resultats obtinguts assenyalen l'important efecte de la posició dels grups metoxi en l'anell aromàtic, sobre la dinàmica molecular del polimetacrilat de benzil. Els espectres obtinguts van ser molt complexos, per aquesta raó per a dur a terme un millor anàlisi es van emprar mètodes numèrics per a la transformació temps-freqüència que van incloure l'ús de tècniques de regularització paramètrica. S'ha estudiat l'efecte que el dit canvi estructural exerceix tant sobre els processos de relaxació secundària com sobre el procés de relaxació , relacionat amb la transició vítria. Així mateix, s'ha analitzat l'efecte de la posició dels grups metoxi en la formació de nanodominis en els que predominen les cadenes laterals, i el seu efecte en els processos de conducció dels materials analitzats. En el Capítol 5 s'arreplega l'estudi de la conductivitat de líquids gomosos prenent com a model el poli-(metacrilat de 2,3-dimetoxibencilo), pel seu peculiar comportament. En aquest capítol s'ha realitzat un anàlisi del principi de superposició temps-temperatura, emprant per a això diferents variables relacionades entre sí. En el Capítol 6 s'arreplega l'efecte de la presència d'entrecreuat en la mobilitat molecular de polimetacrilats que contenen residus d'èters d'alcohols alifàtics. En aquest cas, s'ha analitzat l'efecte de la presència d'entrecreuat tant en els processos de relaxació secundaris, com en el procés de relaxació principal. També es va dur a terme un anàlisi de l'efecte que la presència d'entrecreuat químic té sobre la creació de nanodominis governats per les cadenes laterals.
Carsí Rosique, M. (2015). Molecular mobility. Structure-property relationship of polymeric materials [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/59460
TESIS
Premiado

In this study, the geometric Additive market models are considered. In general, these market models are incomplete, that means: the perfect replication of derivatives, in the usual sense, is not possible. In this study, it is shown that the market can be completed by new artificial assets which are called &ldquo
power-jump assets&rdquo
based on the power-jump processes of the underlying Additive process. Then, the hedging portfolio for claims whose payoff function depends on the prices of the stock and the power-jump assets at maturity is derived. In addition to the previous completion strategy, it is also shown that, using a static hedging formula, the market can also be completed by considering portfolios with a continuum of call options with different strikes and the same maturity. What is more, the portfolio optimization problem is considered in the enlarged market. The optimization problem consists of choosing an optimal portfolio in such a way that the largest expected utility of the terminal wealth is obtained. For particular choices of the equivalent martingale measure, it is shown that the optimal portfolio consists only of bonds and stocks.

The object of the present investigation has been to relate the mechanical properties of a high strength Mg-Y-Gd alloy to alloy composition, extrusion parameters and microstructure. Three alloys with various Y: Gd ratios, of similar total solute content (at %) to Elektron 675, have been investigated in this study:9122: Mg – 6.5 wt % Y – 7.6 wt % Gd – 0.4 wt % Zr 9123: Mg – 8.2 wt % Y – 4.8 wt % Gd – 0.4 wt % Zr9124: Mg – 2.6 wt % Y – 13.1 wt % Gd – 0.4 wt % ZrThe three alloys were extruded at 425 and 475 °C with extrusion ratio 17: 1 to give two samples from each alloy, group a and b. Alloy 9122 was also extruded at 460 and 500 °C with extrusion ratio 10: 1 to give another two samples c and d. The as-cast microstructure of the three alloys comprised equiaxed α-magnesium grains and regions of eutectic decorating some grain boundaries formed during solidification of the ingot. Variation of extrusion parameters has resulted in a dispersion of different volume fractions of second phase particles in different groups of samples. The chemistry of second phase particles was determined by in-situ bulk energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD); magnesium yttrium was identified for near-equiaxed particles and yttrium hydride was proposed as a possible identification for cuboids. The composition of these compounds varied with variation of Y: Gd in the three alloys. Variation of extrusion ratio and extrusion temperature had a clear effect on the evolution of the extruded microstructure and the development of crystallographic texture as characterized by optical microscopy, electron backscattered diffraction (EBSD) and inverse pole figures. The microstructure of the extruded samples was refined during extrusion through dynamic recrystallization (DRX). Samples of groups a, b and c exhibited a microstructure in which bands of fine, equiaxed grains in association with stringers of second phase particles (running along the extrusion direction) were formed between bands of coarse, equiaxed grains. Sample d contained only small volume fraction of second phase particles; only a few alternating bands were formed and considerable grain growth occurred. A random texture was developed during extrusion in samples of groups a, b and c; a wide spread of orientations accompanied by a (new) previously unreported texture component in which basal poles of some grains are aligned nearly parallel to the extrusion direction was developed. The new texture component was weak in sample c and entirely suppressed in sample d. The asymmetry in tensile and compressive yield stress commonly associated with magnesium extrusions was nearly eliminated in samples of group a and b. The new basal texture component was likely to be a result of nucleation of DRX on sites rotating into this orientation. This is proposed to be a result of deformation in those regions in grains was accomodated by basal, prismatic and pyramidal slip. The grains nucleated in this orientation appear to have developed a form of preferred growth which led to strengthening of this new component following solution treatment. The effect of varying solute content (Y & Gd) and different ageing temperatures 150, 200, 250 and 300 °C (T5 & T6) on the ageing response and precipitation reaction were investigated using hardness measurements and transmission electron microscopy (TEM). Alloy 9122 showed the highest ageing response of the three alloys at 150, 200 and 250 °C (T5 & T6); specimens aged in the T5 gave higher hardness than the T6 treatment, a contribution of fine grain size. The three alloys did not respond to ageing at 300 °C. The precipitation reactions that occurred in alloy 9122 (at under, peak and overageing) and alloys 9123 and 9124 (at peak ageing) at 250 °C have been characterized. The precipitation sequence observed in sample 9122a can be described as: . The microstructure of peak aged specimens of alloys 9122 and 9124 were similar; both contained a homogeneous dispersion of precipitates and some metastable precipitates. Alloy 9123 contained only a homogeneous dispersion of precipitates and remnants of precipitates and no precipitates. The enhanced thermal stability of and phases are most likely responsible for the superior elevated temperature properties of Elektron 675. The effect of varying solute content (Y & Gd) and extrusion parameters on the mechanical properties were determined using tensile testing. Alloys 9122 and 9124 exhibited higher 0.2 % proof stress and UTS than alloy 9123 and alloy 9122 was the hardest alloy. Alloy 9122 exhibited the worst ductiliy (T5 and T6) among 9123 and 9124, and this was attributed to the higher volume fraction of second phase particles. The ductility of samples a, b and c in the as-extruded & T5 conditions, particularly in the transverse direction, was limited by stringers of second phase particles, whereas ductility and failure in sample d was governed by grain size and texture. The ductility and failure of all samples aged in the T6 treatment, irrespective of the extrusion history, was controlled by texture and grain size rather than stringers of second phase particles.

Continuous information technology development changed traditional ways of management and business operations. Nowadays there is a high demand for new innovative business solutions and the ways of managing people that enables to fully elicit their potential. Physical boundaries are removed; work is becoming incredibly dispersed around the world enabling growth of 24/7 customer service, home banking, online shopping and other services that were seemed incredible just a few years ago. In this fast paced environment the companies are seeking for any possibility to increase their competitiveness. Implementing flexible working is considered by most of organizations as a tool to adapt to never-ending changes. This paper aims to test the hypothesis that flexible working increases organizational productivity from the perspective of the property as well as from the perspective of employees. In current work organizational productivity from the perspective of property is analyzed from economic standpoint when flexible working decreases operational and real estate costs per employee, thus, allowing saving and investing in other business areas that would increases profitability of the company. Productivity from staff perspective is measured by employee's satisfaction of his working environment, work-life balance, and increased efficiency through team collaboration, flexible hours and telecommuting. Methodology used is case study and literature review. Case study was performed on-site in Alcatel-Lucent in Singapore. It is limited to six months from planned full year of 3 implementation project. Set of interviews with company managers was conducted to support the case results. The thesis suggests the hypothesis, according to the literature review and overview of some cases in different countries, that flexibility in property as well as in working mode increases productivity both in terms of real estate costs savings and in terms of employee’s increased productivity due to better team collaboration in open space, flexible working hours, ability to choose preferred location for work, telecommuting that creates a positive work-life balance. The case study performed for this paper in Alcatel-Lucent Singapore shows that the aforementioned benefits are not there yet due to the project timeline but are highly anticipated by local and global management. Nevertheless, thorough assessment of business requirements and the needs of employees should be undertaken before deciding on flexible working. It is extremely crucial to secure efficient and open internal communication and employees’ involvement in all stages of the project in order to achieve fast acceptance and adaptation to new environment. Based on the current example, future research suggests investigating in cultural aspect of global strategy deployment by corporate decision in different countries.

Free-layer hard or soft coating material can be used for enhancing the inherent damping capacity (energy dissipation ability) of a structure under cyclic bending deformation. This may help to attenuate the vibration amplitude at the resonance frequency. In this study, dynamic mechanical and damping properties of a carbon based (CNx) coating material have been investigated. For determining the material properties of this coating, two samples (600 μm and 800 μm thick carbon nitride (CNx) film layers) were produced and deposited onto two internal turning tools by using the plasma enhanced chemical vapor deposition (PECVD) process. The deposition process was conducted at the room temperature with the magnetron sputtering of a copper and a subsequent graphite target plate in a highly ionized plasma and reactive environment of Ar, N2 and C2H2 gases. Eigen frequencies and system loss factors of the uncoated and coated tools were extracted, for the first two fundamental bending modes (mode X and mode Y), from the ‘drive point’ measurements of free hanging impact tests at the free-free boundary condition. Modulus of elasticity and loss factor of the coating material has been deduced through the comparison between the eigen frequencies and resonance amplitudes of the identical bending modes extracted from the experimental and analytical frequency response functions. The results obtained from the experimental modal analyses and the iterative finite element analyses show that, compared to the substrate, the flexural stiffness and the damping capacity of the coated tools have increased notably. The resonant frequencies of the coated samples have been shifted to the higher frequency levels, and the frequency response acceleration amplitudes have been attenuated dramatically. Elastic modulus and loss factor range of the coating material have been found to be in the range of 32.5 GPa to 49.1 GPa and 0.004 to 0.0245 respectively. Comparison between the analytical frequency response functions of the CNx coating material and 3M-112 viscoelastic material coated samples (for 800 μm film thickness) has anticipated that the coating material has higher loss modulus (energy dissipation ability) as opposed to the viscoelastic material. Scanning electron microscope images of the cross-section of a coated sample have revealed that the frictional energy losses between the interfaces of the carbon-nitride columnar micro-structures dominate the inherent damping mechanism of the coating material. Voids and porosities, present between the columnar clusters, further increase the energy dissipation ability of the coating material by enhancing the interface slippage mechanism during the cyclic bending deformation.

Dan Beaty (1937-2002) was a prolific composer, pianist, researcher, educator, and writer. His large compositional output included chamber works, choral works, songs, orchestral pieces, electronic music, and keyboard works. Beaty was well versed in traditional Western music as well as the more avant-garde and perplexing idioms of the twentieth century. Beaty's compositions reflect the many fascinating, if not always popular, musical trends of his time. His music encompasses styles from serial to jazz, shows compositional influences from Arnold Schoenberg to Indonesian music, and demonstrates thought-provoking and highly intellectual craftsmanship. This document explores several of Beaty's songs through a discussion of the composer's life and compositional process. Songs included in this document are Three Weeks Songs, October, November, A Sappho Lyric, Love Song, That Night When Joy Began, and War Lyrics. This document was written to accompany the author's DMA Lecture-Recital at the University of North Texas. Unfortunately, Beaty's vocal music was never published and is mostly unknown. One goal of the project was to initiate interest in Beaty's songs. Through this document, Lecture-Recital, and additional performances, considerable strides have been made to bring Beaty's songs to new audiences throughout the United States. In addition, the author has received permission from the Beaty family to publish Dan Beaty's songs.

Master of Science
Department of Chemical Engineering
Jennifer L. Anthony
A polymer has drastically different physical properties above versus below some characteristic temperature. For this reason, the precise identification of this glass transition temperature, T[subscript]g, is critical in evaluating product feasibility for a given application. The objective of this report is to review the behavior of polymers near their T[subscript]g and assess the capability of predicting T[subscript]g using theoretical and empirical models. It was determined that all polymers begin to undergo structural relaxation at various temperatures both nearly above and below T[subscript]g, and that practical assessment of a single consistent T[subscript]g is successfully performed through consideration of only immediate thermal history and thermodynamic properties. It was found that the best quantitative structure-property relationship (QSPR) models accurately predict T[subscript]g of polymers of theoretically infinite chain length with an average error of less than 20 K or about 6%, while T[subscript]g prediction for shorter polymers must be done by supplementing these T[subscript]g (∞) values with configurational entropy or molecular weight relational models. These latter models were found to be reliable only for polymers of molecular weight greater than about 2,000 g/mol and possessing a T[subscript]g (∞) of less than about 400 K.

The first part of this thesis is concerned with thestructure-property relationships in nonionic surfactantsystems. The main aim was to investigate how the surfactantstructure influences the adsorption at interfaces andinteractions between surfactant coated interfaces.Particularly, the effect of the structure of the surfactantheadgroups was investigated. These were sugar-based headgroupwith varying size and flexibility and poly(ethylene oxide)based headgroups with or without an additional amide or estergroup. The hydrophobic part of the surfactant consisted mostlyof straight alkyl chains, except for one type of poly(ethyleneoxide) based surfactant with a dehydroabietic hydrophobe.

The main technique that was used is the surface forcetechnique, with which the forces acting between two adsorbedsurfactant layers on hydrophilic or hydrophobic surfaces can bemeasured. These forces are important for e.g. the stability ofdispersions. The hydrophilic surfaces employed were glass andmica, whereas the hydrophobic surfaces were silanized glass andhydrophobized mica. The adsorption behavior on hydrophilicsurfaces is highly dependent on the type of headgroup andsurface, whereas similar results were obtained on the two typesof hydrophobic surfaces. To better understand how the surfaceforces are affected by the surfactant structure, measurementsof adsorbed amount and theoretical mean-field latticecalculations were carried out. The results show that the sugarsurfactant layers and poly(ethylene oxide) surfactant layersgive rise to very different surface forces, but that the forcesare more similar within each group. The structure-propertyrelationships for many other physical properties have beenstudied as well. These include equilibrium and dynamicadsorption at the liquid-vapor interface, micelle size, micelledynamics, and wetting.

The second part in this thesis is about the aggregationbetween cationic polyelectrolytes and an anionic surfactant.The surface force technique was used to study the adsorption ofa low charged cationic polyelectrolyte on mica, and theaggregation between the adsorbed polyelectrolyte with theanionic surfactant. The aggregation in bulk was studied withturbidimetry, small angle neutron scattering (SANS), and smallangle x-ray scattering (SAXS). An internal hexagonal aggregatestructure was found for some of the bulk aggregates.

Keywords:nonionic surfactant, sugar surfactant,poly(ethylene oxide), amide, ester, polyelectrolyte, SDS,hydrophobic surface, glass surface, mica, adsorption,aggregation, micelle size, surface forces, wetting, dynamicsurface tension, NMR, TRFQ, SANS, SAXS, mean-field latticecalculations.

When using timber for construction purposes it is important to know its strength. One way to do this is by sorting the boards into strength classes that are defined by European standards.  A commonly used method for strength grading is based on dynamic excitation in the longitudinal direction of the board to obtain an average dynamic longitudinal modulus of elasticity (MOE). This in turn correlates with the bending strength of the board in such a way that it can be used as an indicating property (IP) to bending strength. The use of MOE as an IP has proven to give the highest coefficient of determination (R2) to both bending and tensile strength in boards. Through the research described in this thesis, one might find that both reducing the length of a board to half its initial length and by removing the part containing the lowest local MOE in edgewise bending provided similar results, the axial dynamic MOE remaining within a 1% tolerance whereas the lowest IP based on local MOE in edgewise bending increased by 6–7%.

A damage detection approach based on Artificial Neural Network (ANN), using the statistics of structural dynamic responses as the damage index, is proposed in this study for Structural Health Monitoring (SHM). Based on the sensitivity analysis, the feasibility of using the changes of variances and covariance of dynamic responses of railway bridges under moving trains as the indices for damage detection is evaluated.   A FE Model of a one-span simply supported beam bridge is built, considering both single damage case and multi-damage case. A Back-Propagation Neural Network (BPNN) is designed and trained to simulate the detection process. A series of numerical tests on the FE model with different train properties prove the validity and efficiency of the proposed approach. The results show not only that the trained ANN together with the statistics can correctly estimate the location and severity of damage in the structure, but also that the identification of the damage location is more difficult than that of the damage severity. In summary, it is concluded that the use of statistical property of structural dynamic response as damage index with the Artificial Neural Network as detection tool for damage detection is reliable and effective.

Dynamic complexity occurs in every social structure. Film industry, as a type of creative industries, constitutes a dynamic environment where uncertainty is at high levels. This complexity of the environment renders the more traditional operations research models somewhat ineffective, and thus, requires a dynamic analysis. In this study, a model showing the dynamics of film exhibition is given. The interactions within and between the theatrical and the DVD sales channels are implemented by the model. Later on, the possible effects of piracy to the model are discussed, using the inferences obtained by the created model. The model is examined with scenario and sensitivity analysis. All the modeling studies are done with a commercial dynamic systems modeling software. The model also can be extended for the whole film industry, or for some other creative industries like the publishing industry.

Increasing societal demand for automation has led to considerable efforts to control large-scale complex systems, especially in the area of autonomous intelligent control methods. The control system of a large-scale complex system needs to satisfy four system level requirements: robustness, flexibility, reusability, and scalability. Corresponding to the four system level requirements, there arise four major challenges. First, it is difficult to get accurate and complete information. Second, the system may be physically highly distributed. Third, the system evolves very quickly. Fourth, emergent global behaviors of the system can be caused by small disturbances at the component level. The Multi-Agent Based Control (MABC) method as an implementation of distributed intelligent control has been the focus of research since the 1970s, in an effort to solve the above-mentioned problems in controlling large-scale complex systems. However, to the author's best knowledge, all MABC systems for large-scale complex systems with significant uncertainties are problem-specific and thus difficult to extend to other domains or larger systems. This situation is partly due to the control architecture of multiple agents being determined by agent to agent coupling and interaction mechanisms. Therefore, the research objective of this dissertation is to develop a comprehensive, generalized framework for the control system design of general large-scale complex systems with significant uncertainties, with the focus on distributed control architecture design and distributed inference engine design. A Hybrid Multi-Agent Based Control (HyMABC) architecture is proposed by combining hierarchical control architecture and module control architecture with logical replication rings. First, it decomposes a complex system hierarchically; second, it combines the components in the same level as a module, and then designs common interfaces for all of the components in the same module; third, replications are made for critical agents and are organized into logical rings. This architecture maintains clear guidelines for complexity decomposition and also increases the robustness of the whole system. Multiple Sectioned Dynamic Bayesian Networks (MSDBNs) as a distributed dynamic probabilistic inference engine, can be embedded into the control architecture to handle uncertainties of general large-scale complex systems. MSDBNs decomposes a large knowledge-based system into many agents. Each agent holds its partial perspective of a large problem domain by representing its knowledge as a Dynamic Bayesian Network (DBN). Each agent accesses local evidence from its corresponding local sensors and communicates with other agents through finite message passing. If the distributed agents can be organized into a tree structure, satisfying the running intersection property and d-sep set requirements, globally consistent inferences are achievable in a distributed way. By using different frequencies for local DBN agent belief updating and global system belief updating, it balances the communication cost with the global consistency of inferences. In this dissertation, a fully factorized Boyen-Koller (BK) approximation algorithm is used for local DBN agent belief updating, and the static Junction Forest Linkage Tree (JFLT) algorithm is used for global system belief updating. MSDBNs assume a static structure and a stable communication network for the whole system. However, for a real system, sub-Bayesian networks as nodes could be lost, and the communication network could be shut down due to partial damage in the system. Therefore, on-line and automatic MSDBNs structure formation is necessary for making robust state estimations and increasing survivability of the whole system. A Distributed Spanning Tree Optimization (DSTO) algorithm, a Distributed D-Sep Set Satisfaction (DDSSS) algorithm, and a Distributed Running Intersection Satisfaction (DRIS) algorithm are proposed in this dissertation. Combining these three distributed algorithms and a Distributed Belief Propagation (DBP) algorithm in MSDBNs makes state estimations robust to partial damage in the whole system. Combining the distributed control architecture design and the distributed inference engine design leads to a process of control system design for a general large-scale complex system. As applications of the proposed methodology, the control system design of a simplified ship chilled water system and a notional ship chilled water system have been demonstrated step by step. Simulation results not only show that the proposed methodology gives a clear guideline for control system design for general large-scale complex systems with dynamic and uncertain environment, but also indicate that the combination of MSDBNs and HyMABC can provide excellent performance for controlling general large-scale complex systems.

Thesis (Ph.D.)--Indiana University, School of Public and Enviromental Affairs and Dept. of Political Science, 2007.
Title from PDF t.p. (viewed Nov. 19, 2008). Source: Dissertation Abstracts International, Volume: 68-02, Section: A, page: 0710. Adviser: Elinor Ostrom.

[EN] The dynamics of linear operators, namely linear dynamics, is mainly concerned with the behaviour of iterates of linear transformations. Hypercyclicity is the study of linear operators that possess a dense orbit. Although the first examples of hypercyclic operators are due to G. D. Birkhoff (in 1929), G. R. MacLane (in 1952) and S. Rolewicz (in 1969), we can date the birth of the linear dynamics in 1982 with the unpublished PhD thesis of C. Kitai. Since then, many mathematicians have contributed to the development of this flourishing new area of the analysis. Linear dynamics connects functional analysis and dynamics. As for the classical dynamical systems, one can study the dynamics of linear operators from a topological point of view. In this context, we state that an operator has the specification property (SP). Precisely, the aim of this PhD thesis is to study the specification property on linear dynamical systems. A continuous map on a compact metric space satisfies the specification property if one can approximate pieces of orbits by a single periodic orbits with a certain uniformity. This Doctoral dissertation is a compendium of articles on the specification property. It is structured in four parts preceded by a chapter which introduces the notation, definitions and the basic results that will be needed throughout the thesis. The shift operators on sequence spaces constitute one of the most important test ground for discrete linear dynamical systems. Due to its simple structure, every time you introduce a new property in linear dynamics it is common to check it on weighted shifts operators. It is for this reason that the first part of this research work is devoted to study the specification property for unilateral and bilateral backward shift operators on weighted l^p-spaces and the relationship with other dynamical properties. In Chapter 3 we extend the results on the SP to shift operators on separable sequence F-spaces. An F-space is a vector space that is endowed with an F-norm and that is complete under the induced metric. The notion of an F-norm has the advantage that one can largely argue as if one was working in a Banach space. One need to be aware of the fact that the positive homogeneity of a norm is no longer available. The spaces l^p with 0 < p < 1 are F-spaces. Chaotic dynamical systems have received a great deal of attention in recent years. An operator is chaotic if it has a dense set of periodic points. The specification property is an interesting and rather strong notion of chaos (in the topological sense). We also consider a qualitative strengthening of hypercyclicity namely frequent hypercyclicity. It was introduced by Bayart and Grivaux, motivated by Birkhoff's ergodic theorem. An operator is frequently hypercyclic if there is some element whose orbit meets every non-empty open set very often. In Chapter 4 the specification property is deeply studied for linear and continuous operators on separable F-spaces. In addition, we are interested in finding out its relation with other dynamical properties such as mixing, Devaney chaos and frequent hypercyclicity. The results that we have achieved have been accepted to be publish in Journal of Mathematical Analysis and Applications. Finally, in the last chapter of this dissertation, we examine the specification property for strongly continuous semigroups on Banach spaces, that is, for C_0-semigroups. They can viewed as the continuous-time analogue of the discrete-time case of iterates of a single operator; in other words, the parameter in the continuous case plays the role of the iterations in the discrete case. Now the translation semigroups substitute the shift operators as test classes. Once again, we study the relationship between the specification property and mixing, chaos and frequent hypercyclicity properties of a C_0-semigroup.
[ES] La dinámica de operadores lineales, o simplemente dinámica lineal, estudia las órbitas generadas por las iteraciones de una transformación lineal. La hiperciclicidad es el estudio de los operadores lineales que poseen una órbita densa. Si bien G. D. Birkhoff (en 1929), G. R. MacLane (en 1952) y S. Rolewicz (en 1969) obtuvieron ejemplos de operadores lineales hipercíclicos, podemos fijar el nacimiento de la dinámica lineal en 1982 con la tesis de C. Kitai. Desde entonces muchos matemáticos han contribuido al desarrollo de esta floreciente área del análisis. La dinámica lineal conecta el análisis funcional y la dinámica. Al igual que en sistemas dinámicos clásicos, podemos estudiar la dinámica de operadores lineales desde un punto de vista topológico. En este contexto, hablamos de que un operador tiene la propiedad de especificación (SP). Precisamente, al estudio de la propiedad de especificación en sistemas dinámicos lineales está dedicada la presente tesis doctoral. Una aplicación continua en un espacio métrico satisface la propiedad de especificación si para cualquier familia de puntos podemos aproximar, con una cierta uniformidad, partes de sus órbitas por una sola órbita de un punto periódico. La tesis es un compendio de artículos sobre la propiedad de especificación. Se estructura en cuatro partes precedidas de un capítulo dedicado a introducir la notación, definir los conceptos y enunciar los resultados de ámbito general que van a ser utilizados en el resto de la memoria. Los operadores "shift" (desplazamiento) constituyen una de las clases más importantes, como campo de pruebas, en sistemas dinámicos lineales discretos. Debido a su estructura simple, siempre que se introduce un nuevo concepto en dinámica lineal es habitual comprobarlo sobre shifts ponderados. Por este motivo, en la primera parte de esta memoria, se estudia la propiedad de especificación para operadores desplazamiento unilaterales y bilaterales en espacios l^p ponderados y la relación con otras propiedades dinámicas. En el capítulo 3 se generalizan los resultados sobre la propiedad SP a operadores desplazamiento en F-espacios separables de sucesiones. Un F-espacio es un espacio vectorial, dotado de una F-norma, que es completo con la métrica inducida. La noción de F-norma tiene la ventaja de que permite trabajar como en un espacio de Banach llevando cuidado con la homogeneidad de la norma que ahora no se cumple Los sistemas dinámicos caóticos han recibido gran atención en los últimos años. Un operador lineal es caótico si admite un conjunto denso de puntos periódicos. La propiedad de especificación es una noción de caos (en el sentido topológico) más potente que la debida a Devaney. Otra variante más fuerte que la hiperciclicidad es la hiperciclicidad frequente. Este concepto fue introducido por Bayart y Grivaux motivados por el teorema ergódico de Birkhoff. Un operador es frecuentemente hipercíclico si algún elemento tiene una órbita que corta muy a menudo a cada conjunto abierto no vacío. En el capítulo 4 de esta tesis se estudia con profundidad la propiedad de especificación para operadores lineales y continuos definidos en F-espacios separables. Los resultados que presentamos han sido aceptados para su publicación en J. Math. Anal. Appl. Finalmente, en la cuarta parte de este trabajo, se extiende la propiedad de especificación a semigrupos de operadores fuertemente continuos en espacios de Banach, esto es, C_0-semigrupos. Estos operadores pueden verse como la versión continua del caso discreto correspondiente a las iteraciones de un único operador. Ahora, la labor de los operadores desplazamiento en espacios de sucesiones como clases de prueba la desempeñan los semigrupos de traslación. Al igual que en capítulos anteriores, se estudia la relación de la propiedad SP para C_0-semigrupos con otras propiedades dinámicas.
[CAT] La dinàmica d'operadors lineals, o simplement dinàmica lineal, estudie les òrbites generades per les iteracions d'una transformació lineal. La hiperciclicitat es el estudi dels operadors lineal que posseeixen una òrbita densa. Si bé G. D. Birkhoff (en 1929), G. R. MacLane (en 1952) y S. Rolewicz (en 1969) van obtenir exemples d'operadors lineals hipercíclics, podem fixar el naixement de la dinàmica lineal en 1982 amb la tesi de C. Kitai [68]. Des de llavors molts matemàtics han contribuït al desenvolupament d'esta florent area de l'anàlisi. La dinàmica lineal connecta el anàlisi funcional y la dinàmica. Igual que en sistemes dinàmics clàssics, podem estudiar la dinàmica d'operadors lineals des d'un punt de vista topològic. En eixe context, parlem que un operador té la propietat d'especificació (SP). Precisament, al estudi de la propietat d'especificació en sistemes dinàmics lineals està dedicada la present tesi doctoral. Una aplicació continua en un espai mètric compleix la propietat d'especificació si per a qualsevol família de punts podem aproximar, amb certa uniformitat, parts de les seues òrbites per una sola òrbita d'un punt periòdic. La tesi es un compendi de articles sobre la propietat d'especificació. S'estructura en quatre parts precedides d'un capítol dedicat a introduir la notació, definir els conceptes i enunciar els resultats d'àmbit general que seran utilitzats en la resta de la memòria. Els operadors "shifts" (desplaçaments) constitueixen una de les classes més importants, com a camp de proves, en sistemes dinàmics lineals discrets. Degut a la seua estructura simple, sempre que es introdueix un nou concepte en dinàmica lineal es habitual comprovar-ho sobre shifts ponderats. Per esta raó, en la primera part d'esta memòria, s'estudia la propietat d'especificació per a operadors desplaçament unilaterals i bilaterals en espais l^p ponderats i la relació amb altres propietats dinàmiques. En el capítol 3 es generalitzen els resultats sobre la propietat SP a operadors desplaçament en F-espais separables de successions. Un F-espai es un espai vectorial, dotat d'una F-norma, que és complet amb la mètrica induida. La noció de F-norma té l'avantatge que permet treballar com en un espai de Banach anant en compte amb l'homogeneitat de la norma que ara no es compleix. Els espais l^p amb 0 < p < 1 són exemples de F-espais. Els sistemes dinàmics caòtics han rebut gran atenció en els últims anys. Un operador lineal és caòtic si admet un conjunt dens de punts periòdics. La propietat d'especificació és una noció de caos (en el sentit topològic) més potent que la deguda a Devaney. Una altra variant més forta que la hiperciclicitat és la hiperciclicitat freqüent. Aquest concepte va ser introduït per Bayart i Grivaux motivats per el teorema ergòdic de Birkhoff. Un operador és freqüentment hipercíclic si algun element té una òrbita que talle molt sovint a cada conjunt obert no vuit. En el capítol 4 d'esta tesi se estudie amb profunditat la propietat d'especificació per a operadors lineals i continus definits en F-espais separables. També s'incideix en la connexió de dita propietat amb altres propietats dinàmiques. Els resultats que presentem han estat acceptats per a la seva publicació en J. Math. Anal. Appl. Finalment, en la quarta part d'aquest treball, s'estén la propietat d'especificació a semigrups d'operadors fortament continus en espais de Banach, això és, C_0-semigrups. Aquests operadors poden veure's com la versió continua del cas discret corresponen a les iteracions d'un únic operador; en altres paraules, el paper de les iteracions en el cas discret ho assumeix el paràmetre en el cas continu. Ara, la labor del operadors desplaçament en espais de successions com classes de prova l'exerceixen els semigrups de translació. Igual que en capítols anteriors, s'estudia la relació de la propietat SP per a C0-semigrups amb altres propie
Bartoll Arnau, S. (2016). The specification property in linear dynamics [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/61633
TESIS

Afin d'étudier l'influence de l'état de la réticulation des matrices thermodurcissables (soc) sur les propriétés mécaniques des composites, nous nous sommes appuyés sur la méthode couplant l'expérimentation et la modélisation (analyse numérique et informatique). Après avoir validé les modèles en comparant les résultats calculés à ceux des expériences réalisées au laboratoire, nous avons préparé des pièces de composite dans des conditions opératoires différentes, donc à des soc différents. Une évolution de la réticulation de la résine en contact avec l'air a été montrée. Nous avons étudié le rôle de l'épaisseur du composite pendant le processus global de la réaction. Plus l'épaisseur de l'échantillon est grande, plus le soc évolue pendant la phase de post-cuisson. Les propriétés mécaniques pour des composites préparés à différents soc ont été étudiées : nous avons comparé la dureté superficielle à celle du cur du matériau : la valeur de cette dernière est plus grande. La dureté est largement dépendante des conditions de préparation du composite, c'est-à-dire de la température et de la durée du chauffage et du refroidissement, ainsi que du mode de refroidissement. L'étude des propriétés mécaniques en dynamique a été réalisée dans le viscoanalyseur en programmation de température, à fréquence constante ou variable. Nous avons choisi le mode de traction-compression. Cette étude s'est avérée intéressante puisque le matériau est viscoélastique. Nous avons pu déterminer l'influence de plusieurs paramètres sur le comportement du matériau (fréquence de vibration et température) ; qui dépend des propriétés mécaniques suivantes : le module de Young élastique e' et l'amortissement tg d. Nous avons déterminé la transition vitreuse du matériau tg. Une corrélation entre le soc et le module e' a été mise en évidence

We have used a molecular modeling of both random and blocky sequence hydrogel networks of poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) (P(VP-co-HEMA)) with a composition of VP:HEMA = 37:13 to investigate the effect of the monomeric sequence and the water content on the equilibrium structures and the mechanical and transport properties by full-atomistic molecular dynamics (MD) simulations. The degree of randomness of the monomer sequence for the random and the blocky copolymers, were 1.170 and 0.104, respectively, and the degree of polymerization was fixed at 50. The equilibrated density of the hydrogel was found to be larger for the random sequence than for the blocky sequence at low water contents (< 40 wt %), but this density difference decreased with increasing water content. The pair correlation function analysis shows that VP is more hydrophilic than HEMA and that the random sequence hydrogel is solvated more than the blocky sequence hydrogel at low water content, which disappears with increasing water content. Correspondingly, the water structure is more disrupted by the random sequence hydrogel at low water content but eventually develops the expected bulk-water-like structure with increasing water content. From mechanical deformation simulations, the stress-strain analysis showed that the VP is found to relax more efficiently, especially in the blocky sequence, so that the blocky sequence hydrogel shows less stress levels compared to the random sequence hydrogel. As the water content increases, the stress level becomes identical for both sequences. The elastic moduli of the hydrogels calculated from the constant strain energy minimization show the same trend with the stress-strain analysis. Ascorbic acid and D-glucose were used to study the effect of the monomeric sequence on the diffusion of small guest molecules within the hydrogels. By analyzing the pair correlation functions, it was found that the guest molecule has greater accessibility to the VP units than to the HEMA units with both monomeric sequences due to its higher hydrophilicity compared to the HEMA units. The monomeric sequence effect on the P(VP-co-HEMA) hydrogel is clearly observed with 20 wt % water content, but the monomeric sequence effect is significantly reduced with 40 wt % water content and disappears with 80 wt % water content. This is because the hydrophilic guest molecules are more likely to be associated with water molecules than with the polymer network at the high water content. By analyzing the mean square displacement, the displacement of the guest molecules and the inner surface area, it is also found that the guest molecule is confined in the system at 20 wt % water content, resulting in highly anomalous subdiffusion. Therefore, the diffusion of the guest molecules is directly affected by their interaction with the monomer units, the monomeric sequence and the geometrical confinement in the hydrogel at a low water content, but the monomeric sequence effect and the restriction on the diffusion of the guest molecule are significantly decreased with increasing the water content. We also investigated the de-swelling mechanisms of the surface-grafted poly(N-isopropylacrylamide) (P(NIPAAm)) brushes containing 1300 water molecules at 275 K, 290 K, 320 K, 345 K, and 370 K. We clearly observed the de-swelling of the water molecules for P(NIPAAm) above the lower critical solution temperature (LCST) (~305 K). Below the LCST, we did not observe the de-swelling of water molecules. Using the upper critical solution temperature (UCST) systems (poly(acrylamide) brushes) for comparison purposes, we did not observe the de-swelling of water molecules at a given range of temperatures. By analyzing the pair correlation functions and the coordination numbers, the de-swelling of the water molecules occurred distinctly around the isopropyl group of the P(NIPAAm) brush above the LCST because C(NIPAAm) does not offer sufficient interaction with the water molecules via the hydrogen bonding type of secondary interaction. We also found that the contribution of the N(NIPAAm)-O(water) pair is quite small because of the steric hindrance of the isopropyl group. By analyzing the change in the hydrogen bonds, the hydrogen bonds between polar groups and water molecules in the P(NIPAAm) brushes weaken with increasing temperature, which leads to the de-swelling of the water molecules out of the brushes above the LCST. Below the LCST, the change in the hydrogen bonds is not significant. Again, the contribution of the NH(NIPAAm)-water pairs is insignificant; the total number of hydrogen bonds is ~20, indicating that the interaction between the NH group and the water molecules is not significant due to steric hindrances. Lastly, we observed that the total surface area of the P(NIPAAm) brushes that is accessible to water molecules is decreased by collapsing the brushes followed by the de-swelling of water molecules above the LCST.

Knowledge management (KM) has rapidly risen to become a popular concept amongst its advocates. Critics claim it is simply old wine in new bottle. It is being touted as one of the significant by-products of an information and knowledge revolution, which may be historically unsurpassed in the comprehensiveness of its impacts on all aspects of human endeavours. Critics say the more things change the more they remain the same. After many centuries of philosophical and economical dialectics, the hitherto accepted role of landed property as a critical factor of production is increasingly being challenged. Nevertheless, it remains a significant variable to the success of many business units and indeed all nations. Hence, any concept, which seeks to impact on the productivity of businesses, must not only impact on the social actors within such organisation but also impact on its structures and processes. An extensive review of literature, by this writer, revealed scant research into the role of these phenomena in project-based sectors and nothing published on property investment and development businesses. Hence, the aim of this research was to determine if commercial property investors are practicing KM in any form and if it leads to any significant change in their investment returns or contribute to the achievement of other corporate goals. It commenced with a brief examination of the philosophical debate on the epistemology and ontology of knowledge. The study established the existing range of expositions on the distinctions between data, information, knowledge, KM and Intellectual Capital Management. Included is a detailed review of KM models and the constraints of outcome measurement. The interplay between organisational culture and employee mindset was considered in addition to the effects of physical workspace on KM. The study followed this with a concise review of the nature of the property industry, the characteristics of commercial property investment, the criteria that impact on investment returns and current drivers of change. Based on initial predilection towards positivism, the Researcher conducted a general survey within the chosen scope of the northwest region of England. Analysis of the returns confirmed that only 11.1% of private commercial property companies are proactively implementing KM, whilst others are still at a lower end of a spectrum that see them implementing information management strategies and traditional estate management practices only. Having purged the research of the initial cognitive predispositions, a reasoned transition from positivistic orthodoxy to a phenomenological paradigm was made and a case study secured amongst the few organisations implementing this practice. The research continued steadily with methodological triangulation as a means of studying the dynamics in the case. An electronic survey of all 179 employees was conducted, followed by additional interviewing of 22 employees and directors. Also data was collected to facilitate secondary analysis of ten years statutory accounts and the previously conducted survey of over 412 customers of the case studied. The study concluded that the management practices in Bruntwood Estates Ltd (a private commercial property investment company) align with the characteristics of the KM phenomena and contributes positively to both its intellectual capital and financial capital. The impacts and shortcomings of the implementation of these practices were elicited as a prelude to the formulation of models that could serve as innovative tools to other players and researchers in the commercial property industry.

Des procédures de classement sont largement utilisées pour décrire les phénomènes observés dans de nombreux domaines des sciences sociales et naturelles, par exemple la sociologie, l’économie, la linguistique, la démographie, la physique, la biologie, etc.Dans cette thèse, nous nous sommes attachés à l’étude des propriétés de classement et des dynamiques sous-jacentes intégrées dans les systèmes complexes. En particulier,nous nous sommes concentrés sur les classements par score ou par prix dans les systèmes sportifs et les classements d’utilisation des mots ou caractères dans les langues humaines. Le but est de comprendre les mécanismes sous-jacents à ces questions en utilisant les méthodes de la physique statistique, de la statistique bayésienne et de la modélisation multi-agents. Les résultats concrets concernent les aspects suivants.Nous avons tout d’abord traité une étude sur les classements par score/prix dans les systèmes sportifs et analysé 40 échantillons de données dans 12 disciplines sportives différentes. Nous avons trouvé des similitudes frappantes dans différents sports, à savoir le fait que la répartition des résultats/prix suit les lois puissance universelles.Nous avons également montré que le principe de Pareto est largement respecté dans de nombreux systèmes sociaux: ainsi 20% des joueurs accumulent 80% des scores et de l’argent. Les données concernant les matchs de tennis en individuels nous ont révélé que lorsque deux joueurs s’affrontent, la probabilité que le joueur de rang supérieur gagne est liée à la différence de rang des deux adversaires. Afin de comprendre les origines de la mise à l’échelle universelle, nous avons proposé un modèle multi-agents,qui peut simuler les matchs de joueurs à travers différentes compétitions. Les résultats de nos simulations sont cohérents avec les résultats empiriques. L’extension du domaine d’étude de la simulation indique que le modèle est assez robuste par rapport aux modifications de certains paramètres. La loi de Zipf est le comportement le plus régulièrement observé dans la linguistique statistique. Elle a dès lors servi de prototype pour les relations entre rang d’apparitions et fréquence d’apparitions (relations rang-fréquence dans la suite du texte) et les lois d’échelle dans les sciences naturelles. Nous avons étudié plusieurs textes, précisé le domaine de validité de la loi de Zipf, et trouvé que la plage de validité augmente lors du mélange de différents textes. Basé sur l’analyse sémantique latente, nous avons proposé un modèle probabiliste, dans lequel nous avons supposé que les mots sont ajoutés au texte avec des probabilités aléatoires, tandis que leur densité a priori est liée, via la statistique bayésienne, aux caractéristiques générales du lexique mental de l’auteur de ce même texte. Notre modèle explique la loi de Zipf ainsi que ses limites de validité, et la généralise aux hautes et basses fréquences et au hapax legomena.Dans une autre étude, nous avons précisé les relations rang-fréquence pour les caractères chinois. Nous avons choisi d’étudier des textes courts en premier, car pour le bien de l’analyse rang fréquence, les longs textes ne sont que des mélanges de textes plus courts, thématiquement homogènes. Nos résultats ont montré que la loi de Zipf appliqués aux caractères chinois tient parfaitement pour des textes assez courts (quelques milliers de caractères différents). Le même domaine de validité est observé pour les textes courts anglais. Nous avons soutenu que les longs textes chinois montrent une structure hiérarchique à deux couches: des caractères dont la fréquence d’apparition suit une loi puissance (première couche) et des caractères dont l’apparition suit une loi exponentielle (deuxième couche)
Ranking procedures are widely used to describe the phenomena in many differentfields of social and natural sciences, e.g., sociology, economics, linguistics, demography,physics, biology, etc. In this dissertation, we dedicated to study the ranking propertiesand underlying dynamics embedded in complex systems. In particular, we focused onthe scores/prizes ranking in sports systems and the words/characters usage ranking inhuman languages. The aim is to understand the mechanisms behind these issues byusing the methods of statistical physics, Bayesian statistics and agent-based modeling.The concrete results concern the following aspects.We took up an interesting topic on the scores/prizes ranking in sports systems, andanalyzed 40 data samples in 12 different sports fields. We found the striking similaritiesin different sports, i.e., the distributions of scores/prizes follow the universal powerlaws. We also showed that the data yielded the Pareto principle extensively observedin many social systems: 20% of the players accumulate 80% of the scores and money.For the tennis head-to-head data, we revealed that when two players compete, theprobability that the higher-ranked player will win is related to the rank difference ofthe two opponents. In order to understand the origins of the universal scaling, weproposed an agent-based model, which can simulate the competitions of players indifferent matches, and results from our simulations are consistent with the empiricalfindings. Extensive simulation studies indicate that the model is quite robust withrespect to the modifications of some parameters.Zipf’s law is the major regularity of statistical linguistics that served as a prototypefor the rank-frequency relations and scaling laws in natural sciences. We investigatedseveral English texts, clarified the valid range of Zipf’s law, and found this valid rangeincreases upon mixing different texts. Based on the latent semantic analysis, we proposeda probabilistic model, in which we assumed that the words are drawn into thetext with random probabilities, while their apriori density relates, via Bayesian statistics,to the general features of mental lexicon of the author who produced the text. Ourmodel explained the Zipf’s law together with the limits of its validity, its generalizationto high and low frequencies and hapax legomena. In another work, we specified the rank-frequency relations for Chinese characters. We chose to study the short texts first, since for the sake of the rank-frequency analysis,long texts are just mixtures of shorter, thematically homogenous pieces. Our resultsshowed that the Zipf’s law for Chinese characters perfectly holds for sufficiently shorttexts (few thousand different characters), and the scenario of its validity is similar tothat for short English texts. We argued long Chinese texts display a two-layer, hierarchicstructure: power-law rank-frequency characters (first layer) and the exponentialones (second layer). The previous results on the invalidity of the Zipf’s law for longtexts are accounted for by showing that in between of the Zipfian range and the regionof very rare characters (hapax legomena) there emerges a range of ranks, wherethe rank-frequency relation is approximately exponential. From comparative analysisof rank-frequency relations for Chinese and English, we suggested the characters playfor Chinese writers the same role as the words for those writing within alphabeticalsystems

Selective Laser Melting (SLM), a laser-based Additive Manufacturing technique has appealed to the bio-medical, automotive, and aerospace industries due to its ability to fabricate geometrically complex parts with tailored properties and high-precision end-use products. The SLM processing parameters highly influence the part quality, microstructure, and mechanical properties. The process-structure-property relationship of the SLM process is not well-understood. In the process-structure study, a quasi-2D model of Micro-Selective Laser Melting process using molecular dynamics is developed to investigate the localized melting and solidification of a randomly-distributed Aluminum nano-powder bed. The rapid solidification in the meltpool reveals the cooling rate dependent homogeneous nucleation of equiaxed grains at the center of the meltpool. Long columnar grains that spread across three layers, equiaxed grains, nano-pores, twin boundaries, and stacking faults are observed in the final solidified nanostructure obtained after ten passes of the laser beam on three layers of Aluminum nano-powder particles. In the structure-property study, the mechanical deformation behavior of the complex cellular structures observed in the SLM-fabricated 316L Stainless Steel is investigated by performing a series of molecular dynamics simulations of uniaxial tension tests. The effects of compositional segregation of alloying elements, distribution of austenite and ferrite phases in the microstructure, subgranular cell sizes, and pre-existing (grown in) nano-twins on the tensile characteristics of the cellular structures are investigated. The highest yield strength is observed when the Nickel concentration in the cell boundary drops very low to form a ferritic phase in the cell boundary. Additionally, the subgranular cell size has an inverse relationship with mechanical strength, and the nano-twinned cells exhibit higher strength in comparison with twin-free cells.
Master of Science
Additive Manufacturing's (AM) rise as a modern manufacturing paradigm has led to the proliferation in the number of materials that can be processed, reduction in the cost and time of manufacturing, and realization of complicated part geometries that were beyond the capabilities of conventional manufacturing. Selective Laser Melting (SLM) is a laser-based AM technique which can produce metallic parts from the fusion of a powder-bed. The SLM processing parameters greatly influence the part's quality, microstructure, and properties. The process-structure-property relationship of the SLM process is not well-understood. In-situ experimental investigation of the physical phenomena taking place during the SLM process is limited because of the very small length and time scales. Computational methods are cost-effective alternatives to the challenging experimental techniques. But, the continuum-based computational models are ineffective in modeling some of the important physical processes such as melting, nucleation and growth of grains during solidification, and the deformation mechanisms at the atomistic scale. Atomistic simulation is a powerful method that can offset the limitations of the continuum models in elucidating the underlying physics of the SLM process. In this work, the influence of the SLM process parameters on the microstructure of the Aluminum nano-powder particles undergoing μ-SLM processing and the mechanical deformation characteristics of the unique cellular structures observed in the SLM-fabricated 316L stainless steel are studied using molecular dynamics simulations. Ten passes of the laser beam on three layers of Aluminum nano-powder particles have unfolded the formation mechanisms of a complex microstructure associated with the SLM process. The study on the deformation mechanisms of 316L stainless steel has revealed the contribution of the cellular structures to its superior mechanical properties.

Quantum cascade laser (QCL) diodes have potential applications in many areas including emissions analysis and explosives detection, but like many solid-state devices they suer from degraded performance at higher temperatures. To alleviate this drawback, the thermal properties of the QCL diodes must be better understood. Using molecular dynamics (MD) and photothermal radiometry (PTR), the thermal conductivity of a representative QCL diode is computed and measured respectively. The MD results demonstrate that size eects are present in the simulated systems, but if these are accounted for by normalization to experimental results the thermal conductivity of the QCL can be reasonably obtained. The cross-plane conductivity is found to be in the range of 1.8 to 4.3 W=m K, while the in-plane results are in the range of 3.7 to 4.0 W=m K. These values compare well with experimental results from the literature for both QCL materials and for AlInAs and GaInAs, which the QCL is composed of. The cross-plane conductivity results are lower than those of either AlInAs or GaInAs, which demonstrates the phonon scattering at the interfaces. The in-plane results are between AlInAs and GaInAs, which is to be expected. The PTR results are less concrete, as there seem to be heat transfer eects active in the samples which are not included in the models used to t the frequency scans. These effects are not 2D heat transfer artifacts nor are they the result of volumetric absorption. It is possible that they are the results of plasmon induction, but this is only supposition. As the data stand, the PTR and MD results are within an order of magnitude of each other and follow reasonable trends, which suggests that both results are not too far o from reality. While the experimental results are not entirely conclusive, the simulations and experiments corroborate each other suciently to warrant further investigation using these techniques. Additionally, the simulations present sucient internal consistency so as to be useful for thermal property investigation independent of the PTR results.

La surveillance de l'état des structures (SHM) joue un rôle crucial dans de nombreux domaines industriels pour garantir la sécurité, la fiabilité et les performances des structures critiques. Le développement de divers types de capteurs, d'analyseurs de données et de systèmes de communication sans fil permettent de récolter in situ des données attestant de l'état de la structure en temps réel via des modules SHM. Cependant, ces derniers requièrent des bases de données propres à la structure en présence ou pas de défauts de différentes natures et de différents niveaux de gravité. La simulation à base de modèles numériques tels que les modèles éléments finis est souvent utilisée pour construire cette base de données et prédire ainsi les indicateurs de défauts dans les structures. Cette approche est très couteuse lorsque le modèle étudié est complexe, ce qui est souvent le cas comptes tenus de la complexité des structures actuelles.Cette thèse s'inscrit dans ce cadre général. Elle traite du problème de l'obtention efficace de caractéristiques sensibles aux défauts de structures composites complexes. Plus spécifiquement, elle vise à définir et à développer des outils numériques efficaces aidant à la surveillance de structures composites complexes. Dans ce cadre, des approches de réduction de modèle et de métamodélisation basées respectivement sur les méthodes d'éléments finis d'onde (WFE) et de krigeage sont proposées et étudiées. L'objectif principal du présent travail est donc d'évaluer le potentiel de l'utilisation conjointe de la WFE et du krigeage pour prédire efficacement les caractéristiques structurelles et dynamiques de structures composites complexes. Cette efficacité est quantifiée par la précision des prédictions et le coût impliqué. Sur la base des propriétés dynamiques prédites, certains indicateurs (tels que les amplitudes, les fréquences propres et les déphasages) sensibles aux défauts sont définis et exploités pour évaluer l'état de santé des structures considérées. Les études réalisées ont montré que la stratégie proposée, à savoir l'association (WFEM, Krigeage), peut assurer une efficacité intéressante se traduisant par une précision appropriée des prédictions des propriétés structurelles et dynamiques mais en impliquant un coût inférieur à celui des calculs basés sur la méthode WFEM. De plus, la stratégie proposée permet de conserver les mêmes niveaux de sensibilité des propriétés dynamiques aux défauts considérés (fissures et délaminage) avec les niveaux de sévérité associés. La stratégie s'est avérée, par ailleurs, plus efficace lors de l'utilisation du krigeage avec un schéma d'échantillonnage adaptatif et intelligent
Structural health monitoring (SHM) plays a crucial role in many industrial fields to ensure the safety, reliability, and performance of critical structures. The development of various types of sensors, data analysis, and wireless communication systems, enables the collection in situ of data attesting to the real-time state of structures within the framework of SHM modules helping for more accurate and automated decision-making processes. However, the SHM modules require data basis characterizing safe and damaged structures. Simulations based on numerical modelling such as finite element methods, are often used to construct this data basis. However, this approach is very time-consuming especially when the finite element model is complex, which is often the case due to the increasing complexity of structures. This thesis is within this framework. Indeed, it deals with the problem of efficiently obtaining damage-sensitive features of complex composite structures. More specifically, it aims to define and develop efficient numerical tools helping for SHM of complex composite structures. Hence, model reduction and metamodeling approaches based on the Wave-finite element (WFE) and Kriging methods respectively are proposed and investigated. So, the main objective of the present work is to assess the potential of the combination of the WFE and kriging metamodeling to be useful and efficient in predicting the structural and dynamic characteristics of complex composite structures. This efficiency is quantified by the prediction accuracy and the involved cost. Based on the predicted dynamic properties, some damage-sensitive indicators (such as amplitudes, natural frequencies, phase shifts) are defined and exploited to evaluate the health status of the considered structures.Based on the accomplished studies, it is shown that the proposed strategy, namely the Kriging-based WFEM, can ensure an interesting efficiency resulting in a suitable accuracy of predictions of the structural and dynamical properties while involving a smaller cost than the WFEM-based calculations. Moreover, the proposed strategy has kept the same sensitivity levels of dynamic properties to the considered damages (cracks and delamination) with the associated indexes. The strategy proved to be more efficient when using the adaptive sampling scheme with kriging

De nos jours, en sciences des simulations, le besoin de réponses en temps réel se fait de plus en plus ressentir. Les applications basées sur des données dynamiques - Dynamic Data-Driven Application Systems ou DDDAS- nous permettent d'obtenir des résultats en temps réel, grâce aux liens existant entre les outils de simulation et les instruments de mesure. Mais pour cela, les DDDAS ont besoin d'outils de simulations précis et rapides. La solution proposée ici consiste à développer une fois pour toute, en différé (ou 'off-line'), la solution la plus générale possible du modèle, intégrant tous les paramètres comme extra-coordonnées. Cet abaque est alors utilisé pour les calculs 'en-ligne'. Mais ceci soulève à son tour le problème des espaces de grande dimension. La technique de la PGD -Proper Generalized Decomposition- permet d'éviter ce fléau, grâce à la représentation séparée des solutions. Le but de ce travail est d'approfondir les possibilités d'estimation des paramètres, de vérification et de contrôle en temps réel. Le champ d'application est le développement d'une nouvelle méthode de contrôle des couches limites, c'est-à-dire le contrôle des écoulements laminaires au-dessus d'une aile d'avion. Cette nouvelle approche est liée au chauffage en discontinu de certain partie de l'aile en utilisant des bandes de résistance électrique. Contrôler le point de transition et de séparation de la couche limite permettrait de réduire la trainée de frottement, ce qui entrainerait une réduction dans la consommation du carburant, ce qui répondrait aux recommandations de ACARE 2020
Nowadays, in simulation-based engineering science, the need of real-time responses is felt more than ever. Dynamic Data-Driven Application systems -DDDAS, thanks to the linkage of the simulation tools with the measurement devices, enable us to achieve real-time computation. But to do so, DDDAS need accurate and fast simulation tools. The solution presented here consists in first computing once and for all, off-line the model's most general solution, introducing all the parameters as extra-coordinates. This abacus is then considered for the on-line purposes. But this, in turn, raises the issue of highly multidimensional spaces. The Proper Generalized Decomposition technique, thanks to its separated representation, allows circumventing this redoubtable curse. The focus of this work is to explore some possibilities in the context of parameter estimation, verification and control in real time. The application of this research is the development of a new boundary control method, i. E. Laminar-flow control over an airfoil. This new approach is associated with the unsteady surface heating regime using electrically resistant strips embedded in the wing skin. The control of the boundary layer separation and transition will provide a reduction in friction drag, and hence a reduction in the fuel consumption, which would comply with the ACARE 2020 requirements

Mestrado em Finanças
O presente estudo tem por objetivo avaliar a potencialidade de aplicar estratégias de cobertura de risco contra a desvalorização de ativos imobiliários de 4 diferentes tipos (industriais, comerciais, escritórios e de todo o tipo de imóveis), com a utilização de produtos derivados (contratos de futuros) e/ou com a utilização de produtos intimamente dependentes da taxa de inflação. O estudo foi realizado para o mercado inglês com dados de frequência mensal para um período de análise que vai desde 01 de janeiro de 1990 a 31 de dezembro de 2010. A medida utilizada nesta pesquisa para verificar a potencialidade de cobertura dos instrumentos enunciados anteriormente é o coeficiente de correlação condicional na forma constante ρ(CCC) e na forma dinâmica ρ(DCC) existente entre os valores dos retornos dos ativos imobiliários e os valores dos retornos dos contratos de futuros e/ou os valores da taxa de inflação. O coeficiente de correlação condicional dinâmico será calculado seguindo-se a metodologia desenvolvida por Robert F. Engle, ver Engle (2002). Mediante os resultados encontrados, onde o valor do coeficiente de correlação condicional na forma constante ρ(CCC) nunca ultrapassou o valor 0,021 para o caso dos contratos de futuros e 0,129 para a inflação e na forma dinâmica ρ(DCC) o valor máximo obtido foi de 0,272 para os contratos de futuros e para a taxa de inflação foi de 0,208, conclui-se que tanto os contratos de futuros analisados como a taxa de inflação, não apresentam o necessário potencial para o estabelecimento de estratégias de cobertura de risco contra a desvalorização dos preços dos diferentes tipos de imóveis estudados. O risco de correlação é muito elevado o que implica estratégias de cobertura muito pouco eficazes. Esta conclusão é válida e aplicável para o mercado Inglês em análise.
This study aims to evaluate the potential of implementing strategies for hedging against the devaluation of real estate assets of four different types (industrial, commercial, offices and all types) with the use of derivatives (plain vanilla futures contracts) and or the use of products who depend on the rate of inflation. The study was conducted for the English market with frequency monthly data analysis for a period ranging from 1 January 1990 to 31 December 2010. The measure used in this study to verify the potential coverage of the instruments listed above is the constant correlation coefficient conditional ρ(CCC) and the dynamic correlation coefficient conditional ρ(DCC) existing between the returns of real estate assets and the independent variables the returns of futures contracts and the value of inflation rate. The dynamic conditional correlation coefficient is calculated following the methodology developed by Robert F. Engle, see Engle (2002). From the results obtained, where the value of the constant correlation coefficient conditional never exceeded the value 0,021 for the case of futures contracts and 0,129 for inflation tax, and the dynamic coefficient the maximum value obtained was 0,272 for the futures contracts and for inflation rate was 0,208, it is concluded that both, futures contracts as the rate of inflation, do not exhibit the potential to establish strategies of hedging against the devaluation of the prices of different types of properties studied, because the correlation risk is very high. This conclusion is valid and applicable to the market examined that is English market.

Studies have revealed intense competition over land in Chittagong Hill Tracts (CHT) of Bangladesh. This study examines land dispute processes within and between hill people (Chakma Community) and Bengali settlers (who migrated through government initiated settlement program in 1979) in CHT. By understanding property, identity and authority as relational; my study explores mutually constitutive processes between property and authority relations, and between property and identity relations. It investigates how property in land is claimed and defined in the context of dynamic authority relation in land control, multiple categorisations and identity claims in CHT. By carrying out a historical analysis of state-making, I argue that CHT remains a frontier because of- the distinctive legal and administrative systems, ambivalence in property system, ongoing processes of reconfiguration of institutional arrangements in land control and state’s territorial strategies to control its population and space. The study employs an ethnographic approach and data are collected by engaging with disputants, institutional actors, academics, members of political organizations and civil society. Working across communities has enabled to encompass differences in narratives, practices and claims based on varied rules, sources of authority, history and identities. Dispute processes reveal that competing property claims are based on various norms (customary and statutory), varieties of land documents (formal and informal) and wide number of authority sources (formal and informal). Property rules (statutory and customary) are negotiated, continuously interpreted and reinterpreted through practices and claim-making. The findings show that in different kinds of disputes (within and between communities), there are different sets of authorities involved in recognising property in land. The study draws out various political constellation of institutions and authority relations that are formed through competition for authorising land relation. State institutions- bureaucratic, judiciary, regional government, traditional institutions, military authorities; and non-state authorities (political parties, leaders, brokers), all partake and compete in the process of constitution of property relation in ‘post’ conflict/mid conflict zone, suggesting that state-making or control over land/territory and property claims as an active and contested process. While the state rules and institutional competition for authority matter in shaping dispute processes, this study finds that land contestations are evolving through contestation over dakhal i.e. physical or forceful occupation of land, which depends on local authority structure for endorsement, individual’s/disputant’s position in the local power structure, proximity of the army camp and people’s ability to exist on the ground by taking certain strategies and actions. The research findings show that identity formation and social positioning play significant roles in competition over land. Struggle over recognition of property in land is intricately linked to people’s struggle for recognition of certain identities. Religious identities of Chakmas (Buddhist) and Bengalis (Muslim) are increasingly becoming stronger. Besides, religious identities are mobilised in relation to contestation over land. The study provides an account of recurrent and interrelated processes of constitution of property, authority and identity relations in a frontier region, which has also been at the margin of the state historically. In the absence of tenure security, the existing stalemate situation regarding the formalisation process and non-recognition of customary land rights of hill people, it is crucial to understand existing land relations in order to plan and implement development policies, particularly those related to land and forest in CHT. My research has taken a novel approach in studying land conflicts by investigating the making of property, authority and identity relations in a contested territory. It contributes to existing knowledge regarding land relations and related processes of authority and identity formation in CHT, and in regions that can be characterised as frontiers or at the margin of the state.

Thesis (M.S.)--Worcester Polytechnic Institute.
Keywords: material property; thermometer; cone calorimeter; finite difference method; thermoplastic; pyrolysis model; fire dynamics simulators Includes bibliographical references. (p.162-163)

Smooth maps with singularities describe important physical phenomena such as the collisions of rigid spheres among them and/or with the walls of a container. Questions about the ergodic properties of these models (which can be mapped into billiard models) were first raised by Boltzmann in the nineteenth century and lie at the foundation of Statistical Mechanics. Billiard models also describe the diffusive motion of electrons bouncing off positive nuclei (Lorentz gas models) and in this situation the physical measure can be considered infinite. It is therefore of great importance to study the ergodic properties of maps when the measure they preserves is infinite. The aim of this thesis is to present an original result on smooth maps with singularities which preserve an infinite measure. Such result establishes the atomicity of the tail $\sigma$-algebra (and hence strong chaotic properties) in the presence of a totally conservative behavior.

Cette thèse porte sur l’expressivité de la logique du premier ordre et d’autres formalismes sur différentes classes de structures ordonnées, parmi lesquelles les MSC (Message Sequence Charts), un modèle standard pour les exécutions de systèmes concurrents avec échange de messages. Cette étude est motivée par deux questions classiques : celle de l’équivalence, pour certaines classes de structures, entre la logique du premier ordre et son fragment avec k variables, et celle de la comparaison entre automates et logique, dans l’esprit du théorème de Büchi-Elgot-Trakhtenbrot. Notre approche repose sur la logique dynamique propositionnelle sans étoile (PDL sans étoile), une variante de PDL équivalente à la logique du premier ordre avec 3 variables. On étudie d’abord l’expressivité de PDL sans étoile sur des structures linéairement ordonnées avec des prédicats unaires et binaires. On montre que sous certaines conditions de monotonie, PDL sans étoile devient aussi expressive que la logique du premier ordre. Cela implique que toute formule de la logique du premier ordre peut alors être réécrite en une formule équivalente qui utilise au plus 3 variables. Ce résultat s’applique, directement ou indirectement, à un certain nombre de classes naturelles, généralisant des résultats connus et répondant à des questions ouvertes.On se concentre ensuite sur les MSC, auxquels ce premier résultat s’applique également. PDL sans étoile nous permet d’aborder un autre problème important: celui de la synthèse d’automates communicants à partir de spécifications écrites en logique du premier ordre. Les automates communicants sont un modèle de systèmes concurrents dans lequel un nombre fixé d’automates finis échangent des messages via des canaux FIFO. Ils définissent des langages de MSC. Bien que des caractérisations de l’expressivité des automates communicants aient déjà été établies pour certaines restrictions (borne sur la taille des canaux de communications, ou omission de la relation “arrivé-avant” au niveau de la logique), la question suivante restait ouverte dans le cas général : toute formule du premier ordre sur les MSC peut-elle être traduite en un automate communicant équivalent ? On montre que c’est le cas, en utilisant PDL sans étoile comme langage intermédiaire
This thesis is concerned with the expressive power of first-order logic and other formalisms over different classes of ordered structures, among which MSCs (Message Sequence Charts), a standard model for executions of message-passing systems. This study is motivated by two classic problems: the k-variable property, that is, the equivalence of first-order logic and its k-variable fragment over certain classes of structures, and the study of logic-automata connections, in the spirit of Büchi-Elgot-Trakhtenbrot theorem. Our approach relies on star-free propositional dynamic logic (star-free PDL), a variant of PDL with the same expressive power as the 3-variable fragment of first-order logic. We start by studying the expressive power of star-free PDL over linearly ordered structures with unary and binary predicates. We show that under certain monotonicity conditions, star-free PDL becomes as expressive as first-order logic. This implies that any first-order formula can then be rewritten into an equivalent formula with at most 3 variables. This result applies to various natural classes of structures, generalizing several known results and answering some open questions.We then focus on MSCs, to which this first result also applies. We use star-free PDL to address another important problem: the synthesis of communicating finite-state machines (CFMs) from first-order specifications. CFMs are a model of concurrent systems in which a fixed number of finite-state automata communicate through unbounded FIFO channels. They accept languages of MSCs. While logical characterizations of the expressive power of CFMs have been established under different restrictions (bounding the size of the communication channels, or removing the “happened-before” relation from the logic), the following question had remained open in the general case: can every first-order formula over MSCs be translated into an equivalent CFM? We prove that this is the case, using star-free PDL as an intermediate language

Nanocrystalline materials have been under extensive study in the past two decades. The reduction in grain size induces many abnormal behaviors in the properties of nanocrystalline materials, that have been investigated systematically and quantitatively. As one of the most fundamental relations in materials science, the structure-property relation should still apply on materials of nano-scale grain sizes. The characterization of grain boundaries (GBs) and related entities remains a big obstacle to understanding the structure-property relation in nanocrystalline materials. It is challenging experimentally to determine the topological properties of polycrystalline materials due to the complex and disordered grain boundary network presented in the nanocrystalline materials. The constantly improving computing power enables us to study the structure-property relation in nanocrystalline materials via Monte Carlo and molecular dynamic simulations. In this study, we will first propose a geometrical construction method based on inverse Monte Carlo simulation to generate digital microstructures with desired topological properties such as grain size, interface area, triple junction length as well as their statistical distributions. The influences on the grain shapes by different topological properties are studied. Two empirical geometrical laws are examined including the Lewis rule and Aboav-Weaire law. Secondly, defect free nanocrystalline Copper (nc-Cu) samples are generated by filling atoms into the Voronoi structure and then relaxed by molecular dynamics simulations. Atoms in the relaxed nc-Cu samples are then characterized into grain atoms, GB interface atoms, GB triple junction atoms and vertex atoms using a newly proposed method. Atoms in each GB entity can also be identified. Next, the topological properties of nc-Cu samples before and after relaxation are calculated and compared, indicating that there exists a physical limit in the number of atoms to form a stable grain boundary interface and triple junction in nanocrystalline materials. In addition, we are able to obtain the statistical averages of geometrical and thermal properties of atoms across each GB interfaces, the so-called GB profiles, and study the grain size, misorientation and temperature effects on the microstructures in nanocrystalline materials. Finally, nc-Cu samples with different topological properties are deformed under simple shear using MD simulation in an attempt to study the structure-property relation in nanocrystalline materials.

In this thesis we examined the export dynamics at the firm level. A two period model is proposed for the life of firms. The firms may have three different behaviors: staying out of markets, producing for the domestic market, and producing for both the domestic and the export markets. During two periods, firms may enter or exit the markets according to their expected) profits. All firms are profit maximizing such that they compare the maximum (expected) profits in the domestic and export markets. Firms are also heterogenous so that they have different levels of productivity. We examined changes in investment, market share and profits with respect to changes in the market and firm parameters. The profits and investments of the exporting and non-exporting firms are compared by both analytical and numerical methods.

This thesis discusses three distinct topics. A topological space X is said to be self- Tietze if for every closed C eX, every continuous f: C -+ X admits a continuous extension F: X -+ X. We show that every disconnected, self- Tietze space is ultranormal. The Tychonoff Plank is an example of a compact self- Tietze space which is not completely normal, and we establish that a completely normal, zero- dimensional, homogeneous space need not be self- Tietze. A subset of the plane is a two-point set if it meets every straight line in exactly two points. We show that a two-point set cannot contain a dense G8 subset of an arc. We also show that the complement of a two-point set is necessarily path-connected. Finally, we construct a zero-dimensional subset of the plane of which the complement is simply-connected. For A E lR, the tent-map with slope A is the function f: [0, 1] -+ lR such that f(x) = AX for x :=:; ~ and f(x) = A(l - x) for x ~ ~. Properties of w-limit sets of tent-maps, i.e. sets of the form n {fn+k(x) I kEN} nEN for x E [0,1], are examined, and an example of a tent-map and a closed, invariant, nonempty, internally chain transitive subset of [0, 1] which is not an w-limit set is given.

Despite the importance of proper synaptogenesis in the CNS, the molecular mechanisms that regulate the formation and development of synapses remain poorly understood. Indeed, the mechanisms through which initial synaptic contacts are established and modified during synaptogenesis have not been fully determined and a precise understanding of these mechanisms may shed light on synaptic development, plasticity and many CNS developmental diseases. The development and formation of spiny synapses has been thought to occur via filopodia shortening followed by the recruitment of proper postsynaptic proteins, however the precise function of filopodia remains controversial. Thus the goal of this study was to investigate the dynamics of dendritic filopodia and determine their role in the development of synaptic contacts. We initially define and characterize short lipidated motifs that are sufficient to induce process outgrowth. Indeed, the palmitoylated protein motifs of GAP-43 and paralemmin are sufficient to induce filopodial extensions in heterologous cells and to increase the number of filopodia and dendritic branches in neurons. We showed that the morphological changes induced by these FIMs (filopodia inducing motifs) require on-going protein palmitoylation and are modulated by a specific GTPase, Cdc42, that regulates actin dynamics. We also show that their function is palmitoylation dependent and is dynamically regulated by reversible protein palmitoylation. Significantly, our work suggests a general role for those palmitoylated motifs in the development of structures important for synapse formation and maturation. We combined several approaches to monitor the formation and development of filopodia. We show that filopodia continuously explore the environment and probe for appropriate contacts with presynaptic partners. We find that shortly after establishing a contact with axons, filopodia induce the recruitment of presynaptic elements. Remarkably, we find that expression of acylated motifs or the constitutively active form of cdc-42 enhances filopodia number and motility, but reduces the recruitment of synaptophysin positive presynaptic elements and the probability of forming stable axo-dendritic contacts. We provide evidence for the rapid transformation of filopodia to spines within hours of imaging live neurons and reveal potential molecules that accelerate this process.

This work motivates the study of open dynamical systems corresponding to the doubling map. In particular, the dynamical properties of the attractor of the doubling map when a symmetric, centred open interval is removed are studied. Using the arithmetical properties of the binary expansion of the points on the boundary of the removed interval, we study properties such as topological transitivity, the specification property and intrinsic ergodicity. The properties of the function that associates to each hole $(a,b)$ the topological entropy of the attractor of the considered dynamical system are also shown. For these purposes, a subshift corresponding to an element of the lexicographic world is associated to each attractor and the mentioned properties are studied symbolically.