The purpose of this paper is to generalize regression models for repeated categorical data based on maximizing a conditional likelihood. Some existing methods, such as those proposed by Duncan (1985), Fischer (1989), and Agresti (1993, and 1997) are special cases of this latent variable approach, used to account for dependencies in clustered observations. The generalization concerns the incorporation of rather general data structures such as subject-specific time-dependent covariates, a variable number of observations per subject and time periods of arbitrary length in order to evaluate treatment effects on a categorical response variable via a linear parameterization. The response may be polytomous, ordinal or dichotomous. The main tool is the log-linear representation of appropriately parameterized Rasch-type models, which can be fitted using standard software, e.g., R. The proposed method is applied to data from a psychiatric study on the evaluation of psychobiological variables in the therapy of depression. The effects of plasma levels of the antidepressant drug Clomipramine and neuroendocrinological variables on the presence or absence of anxiety symptoms in 45 female patients are analyzed. The individual measurements of the time dependent variables were recorded on 2 to 11 occasions. The findings show that certain combinations of the variables investigated are favorable for the treatment outcome. (author´s abstract) / Series: Research Report Series / Department of Statistics and Mathematics

There are many semiconductors with nominally superior electronic properties compared to silicon. However, silicon became the material of choice for MOSFETs due to its robust native oxide. With Moore's observation as a guiding principle, the semiconductor industry has come a long way in scaling the silicon MOSFETs to smaller dimensions every generation with engineering ingenuity and technological innovation. As per the 2012 International Technology Roadmap for Semiconductors (ITRS), the MOSFET is expected to be scaled to near 6 nm gate length by 2025. However, materials, design and fabrication capabilities aside, basic physical considerations such as source to drain quantum mechanical tunneling, channel to gate tunneling, and thermionic emission over the channel barrier suggest an end to the roadmap for CMOS is on the horizon. The semiconductor industry is already aggressively looking for the next switch which can replace the silicon FET in the long term. My Ph.D. research is part of the quest for the next switch. The promises of process compatibility with existing CMOS technologies, fast carriers with high mobilities, and symmetric conduction and valence bands have led to graphene being considered as a possible alternative to silicon. This work looks at three devices based on graphene using first principles atomistic transport simulations and compact models capturing essential physics: the large-area graphene RF FET, the Bilayer pseudoSpin FET, and the double electron layer resonant tunneling transistor. The characteristics and performance of each device is explored with a combination of SPICE simulations and atomistic quasi static transport simulations. The BiSFET device was found to be a promising alternative to CMOS due to extremely low power dissipation. Finally, I have presented formalism for efficient simulation of time dependent transport in graphene for beyond quasi static performance analysis of the graphene based devices explored in this work. / text

Due to their structural efficiency and architectural elegance, concrete arches have long been used in bridge applications. However, the construction of concrete arches requires significant temporary supporting structures, which prevent their widespread use in modern bridges. A relatively new form of arch bridges is the network arch, in which a dense arrangement of inclined hangers is used. Network arches are subjected to considerably smaller bending moments and deflections than traditional arches and are therefore suitable for modern, accelerated construction methods in which the arches are fabricated off-site and then transported to the bridge location. However, service-level stresses, which play a critical role in the performance of the structure, are relatively unknown for concrete network arches and have not been sufficiently investigated in the previous research on concrete arches. The primary objective of this dissertation is to improve the understanding of short-term and time-dependent stresses in concrete arches, and more specifically, concrete network arches. The research presented herein includes extensive field monitoring of the West 7th Street Bridge in Fort Worth, Texas, which is the first precast network arch bridge and probably the first concrete network arch bridge in the world. The bridge consists of twelve identically designed concrete network arches that were precast and post-tensioned before they were transported to the bridge site and erected. A series of vibrating wire gages were embedded in the arches and were monitored throughout the construction and for a few months after the bridge was opened to traffic. The obtained data were processed, and structural response parameters were evaluated to support the safe construction of the innovative arches, identify their short-term and time-dependent structural behavior, and verify the modeling assumptions. The variability of stresses among the arches was also used to assess the reliability of stress calculations. The results of this study provide valuable insight into the elastic, thermal, and time-dependent behavior of concrete arches in general and concrete network arches in particular. The knowledge gained in this investigation also has broader applications towards understanding the behavior of indeterminate prestressed concrete structures that are subjected to variable boundary conditions and thermal and time-dependent effects.

Traditionally coupled field reactor analysis has been carried out using several loosely coupled solvers, each having been developed independently from the others. In the field of multi-physics, the current generation of object-oriented toolkits provides robust close coupling of multiple fields on a single framework. This research investigates the suitability of such frameworks, in particular the Open-source Field Operation and Manipulation (OpenFOAM) framework, for the solution of spatial reactor dynamics problems. For this a subset of the theory of the Time-dependent Neutronics and Temperatures (TINTE) code, a time-dependent two-group diffusion solver, was implemented in the OpenFOAM framework. This newly created code, called diffusionFOAM, was tested for a number of steady-state and transient cases. The solver was found to perform satisfactorily, despite a number of numerical issues. The object-oriented structure of the framework allowed for rapid and efficient development of the solver. Further investigations suggest that more advanced transport methods and higher order spatial discretization schemes can potentially be implemented using such a framework as well. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2008.

Traditionally coupled field reactor analysis has been carried out using several loosely coupled solvers, each having been developed independently from the others. In the field of multi-physics, the current generation of object-oriented toolkits provides robust close coupling of multiple fields on a single framework. This research investigates the suitability of such frameworks, in particular the Open-source Field Operation and Manipulation (OpenFOAM) framework, for the solution of spatial reactor dynamics problems. For this a subset of the theory of the Time-dependent Neutronics and Temperatures (TINTE) code, a time-dependent two-group diffusion solver, was implemented in the OpenFOAM framework. This newly created code, called diffusionFOAM, was tested for a number of steady-state and transient cases. The solver was found to perform satisfactorily, despite a number of numerical issues. The object-oriented structure of the framework allowed for rapid and efficient development of the solver. Further investigations suggest that more advanced transport methods and higher order spatial discretization schemes can potentially be implemented using such a framework as well. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2008.

Accurate numerical solution of time-dependent, high-dimensional partial differential equations (PDEs) usually requires efficient numerical techniques and massive-scale parallel computing. In this thesis, we implement and evaluate discretization schemes suited for PDEs of higher dimensionality, focusing on high order of accuracy and low computational cost. Spatial discretization is particularly challenging in higher dimensions. The memory requirements for uniform grids quickly grow out of reach even on large-scale parallel computers. We utilize high-order discretization schemes and implement adaptive mesh refinement on structured hyperrectangular domains in order to reduce the required number of grid points and computational work. We allow for anisotropic (non-uniform) refinement by recursive bisection and show how to construct, manage and load balance such grids efficiently. In our numerical examples, we use finite difference schemes to discretize the PDEs. In the adaptive case we show how a stable discretization can be constructed using SBP-SAT operators. However, our adaptive mesh framework is general and other methods of discretization are viable. For integration in time, we implement exponential integrators based on the Lanczos/Arnoldi iterative schemes for eigenvalue approximations. Using adaptive time stepping and a truncated Magnus expansion, we attain high levels of accuracy in the solution at low computational cost. We further investigate alternative implementations of the Lanczos algorithm with reduced communication costs. As an example application problem, we have considered the time-dependent Schrödinger equation (TDSE). We present solvers and results for the solution of the TDSE on equidistant as well as adaptively refined Cartesian grids. / eSSENCE

The main focus of this thesis is Markovian decision processes with an emphasis on incorporating time-dependence into the system dynamics. When considering such decision processes, we provide value equations that apply to a large range of classes of Markovian decision processes, including Markov decision processes (MDPs) and semi-Markov decision processes (SMDPs), time-homogeneous or otherwise. We then formulate a simple decision process with exponential state transitions and solve this decision process using two separate techniques. The first technique solves the value equations directly, and the second utilizes an existing continuous-time MDP solution technique. To incorporate time-dependence into the transition dynamics of the process, we examine a particular decision process with state transitions determined by the Erlang distribution. Although this process is originally classed as a generalized semi-Markov decision process, we re-define it as a time-inhomogeneous SMDP. We show that even for a simply stated process with desirable state-space properties, the complexity of the value equations becomes so substantial that useful analytic expressions for the optimal solutions for all states of the process are unattainable. We develop a new technique, utilizing phase-type (PH) distributions, in an effort to address these complexity issues. By using PH representations, we construct a new state-space for the process, referred to as the phase-space, incorporating the phases of the state transition probability distributions. In performing this step, we effectively model the original process as a continuous-time MDP. The information available in this system is, however, richer than that of the original system. In the interest of maintaining the physical characteristics of the original system, we define a new valuation technique for the phase-space that shields some of this information from the decision maker. Using the process of phase-space construction and our valuation technique, we define an original system of value equations for this phasespace that are equivalent to those for the general Markovian decision processes mentioned earlier. An example of our own phase-space technique is given for the aforementioned Erlang decision process and we identify certain characteristics of the optimal solution such that, when applicable, the implementation of our phase-space technique is greatly simplified. These newly defined value equations for the phase-space are potentially as complex to solve as those defined for the original model. Restricting our focus to systems with acyclic state-spaces though, we describe a top-down approach to solution of the phase-space value equations for more general processes than those considered thus far. Again, we identify characteristics of the optimal solution to look for when implementing this technique and provide simplifications of the value equations where these characteristics are present. We note, however, that it is almost impossible to determine a priori the class of processes for which the simplifications outlined in our phase-space technique will be applicable. Nevertheless, we do no worse in terms of complexity by utilizing our phase-space technique, and leave open the opportunity to simplify the solution process if an appropriate situation arises. The phase-space technique can handle time-dependence in the state transition probabilities, but is insufficient for any process with time-dependent reward structures or discounting. To address such decision processes, we define an approximation technique for the solution of the class of infinite horizon decision processes whose state transitions and reward structures are described with reference to a single global clock. This technique discretizes time into exponentially distributed length intervals and incorporates this absolute time information into the state-space. For processes where the state-transitions are not exponentially distributed, we use the hazard rates of the transition probability distributions evaluated at the discrete time points to model the transition dynamics of the system. We provide a suitable reward structure approximation using our discrete time points and guidelines for sensible truncation, using an MDP approximation to the tail behaviour of the original infinite horizon process. The result is a finite-state time-homogeneous MDP approximation to the original process and this MDP may be solved using standard existing solution techniques. The approximate solution to the original process can then be inferred from the solution to our MDP approximation. / Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Sciences, 2008

In a peer-to-peer shared ride system, transportation clients with traffic demand negotiate with transportation hosts offering shared ride services for ad-hoc ridesharing in a continuously changing environment, using wireless geosensor networks. Due to the distinctive characteristic of this system—a complex and non-deterministic transportation network, and a local peer-to-peer communication strategy—clients will always have limited transportation knowledge, both from a spatial and a temporal perspective. Clients hear only from nearby hosts, and they do not know the future availability of current or new hosts. Clients can plan optimal trips prior to departure according to their current knowledge, but it is unlikely that these trips will be final optimal trip due to continuously changing traffic conditions. Therefore, it is necessary to evaluate the trip quality in this dynamic environment in order to assess different communication and wayfinding strategies. (For complete abstract open document)

Doctor of Philosophy / Department of Chemistry / Christine Aikens / Thiolate-protected noble metal nanoparticles (~2 nm size) are efficient solar photon harvesters, as they favorably absorb within the visible region. Clear mechanistic insights regarding the photo-physics of the excited state dynamics in thiolate-protected noble metal nanoclusters are important for future photocatalytic, light harvesting and photoluminescence applications. Herein, the core and higher excited states lying in the visible range are investigated using the time-dependent density functional theory method for different thiolate-protected nanoclusters. Nonadiabatic molecular dynamics simulations are performed using the fewest switches surface hopping approach with a time-dependent Kohn-Sham (FSSH-TDKS) description of the electronic states with decoherence corrections to study the electronic relaxation dynamics. Calculations on the [Au₂₅ (SH)₁₈]⁻¹ nanocluster showed that relaxations between core excited states occur on a short time scale (2-18 ps). No semiring or other states were observed at an energy lower than the core-based S₁ state, which suggested that the experimentally observed picosecond time constants could be core-to-core transitions rather than core-to-semiring transitions. Electronic relaxation dynamics on [Au₂₅ (SH)₁₈]⁻¹ with different R ligands (R = CH₃, C₂H₅, C₃H₇, MPA) [MPA = mercaptopropanoic acid] showed that all ligand clusters including the simplest SH model follow a similar trend in decay within the core states. In the presence of higher excited states, R= H, CH₃, C₂H₅, C₃H₇ demonstrated similar relaxations trends, whereas R=MPA showed a different relaxation of core states due to a smaller LUMO+1-LUMO+2 gap. Overall, the S₁ state gave the slowest decay in all ligated clusters. An examination of separate electron and hole relaxations in the [Au₂₅ (SCH₃)₁₈]⁻¹ nanocluster showed how the independent electron and hole relaxations contribute to its overall relaxation dynamics. Relaxation dynamics in the Au₁₈(SH)₁₄ nanocluster revealed that the S₁ state has the slowest decay, which is a semiring to core charge transfer state. Hole relaxations are faster than electron relaxations in the Au₁₈(SH)₁₄ cluster due its closely packed HOMOs. The dynamics in the Au₃₈(SH)₂₄ nanocluster predicted that the slowest decay, the decay of S₁₁ or the combined S₁₁-S₁₂, S₁-S₂-S₄-S₇ and S₄-S₅-S₉-S₁₀ decay, involves intracore relaxations. The phonon spectral densities and vibrational frequencies suggested that the low frequency (25 cm⁻¹) coherent phonon emission reported experimentally could be the bending of the bi-icosahedral Au₂₃ core or the “fan blade twisting” mode of two icosahedral units. Relaxation dynamics of the silver nanoparticle [Ag₂₅ (SR)₁₈]⁻¹ showed that both [Ag₂₅(SH)₁₈]⁻¹ and [Au₂₅ (SH)₁₈]⁻¹ follow a common decay trend within the core states and the higher excited states.

CHUCRE, Mirla Rafaela Rafael Braga. K-nearest neighbors queries in time-dependent road networks: analyzing scenarios where points of interest move to the query point. 2015. 65 f. Dissertação (Mestrado em Ciência da Computação)-Universidade Federal do Ceará, Fortaleza, 2015. / Submitted by Jonatas Martins (jonatasmartins@lia.ufc.br) on 2017-06-29T12:26:58Z No. of bitstreams: 1 2015_dis_mrrbchucre.pdf: 15845328 bytes, checksum: a2e4d0a03ca943372c92852d4bcf7236 (MD5) / Approved for entry into archive by Rocilda Sales (rocilda@ufc.br) on 2017-06-29T13:54:36Z (GMT) No. of bitstreams: 1 2015_dis_mrrbchucre.pdf: 15845328 bytes, checksum: a2e4d0a03ca943372c92852d4bcf7236 (MD5) / Made available in DSpace on 2017-06-29T13:54:36Z (GMT). No. of bitstreams: 1 2015_dis_mrrbchucre.pdf: 15845328 bytes, checksum: a2e4d0a03ca943372c92852d4bcf7236 (MD5) Previous issue date: 2015 / A kNN query retrieve the k points of interest that are closest to the query point, where proximity is computed from the query point to the points of interest. Time-dependent road networks are represented as weighted graphs, where the weight of an edge depends on the time one passes through that edge. This way, we can model periodic congestions during rush hour and similar effects. Travel time on road networks heavily depends on the traffic and, typically, the time a moving object takes to traverse a segment depends on departure time. In time-dependent networks, a kNN query, called TD-kNN, returns the k points of interest with minimum travel-time from the query point. As a more concrete example, consider the following scenario. Imagine a tourist in Paris who is interested to visit the touristic attraction closest from him/her. Let us consider two points of interest in the city, the Eiffel Tower and the Cathedral of Notre Dame. He/she asks a query asking for the touristic attraction whose the path leading up to it is the fastest at that time, the answer depends on the departure time. For example, at 10h it takes 10 minutes to go to the Cathedral. It is the nearest attraction. Although, if he/she asks the same query at 22h, in the same spatial point, the nearest attraction is the Eiffel Tower. In this work, we identify a variation of nearest neighbors queries in time-dependent road networks that has wide applications and requires novel algorithms for processing. Differently from TD-kNN queries, we aim at minimizing the travel time from points of interest to the query point. With this approach, a cab company can find the nearest taxi in time to a passenger requesting transportation. More specifically, we address the following query: find the k points of interest (e.g. taxi drivers) which can move to the query point (e.g. a taxi user) in the minimum amount of time. Previous works have proposed solutions to answer kNN queries considering the time dependency of the network but not computing the proximity from the points of interest to the query point. We propose and discuss a solution to this type of query which are based on the previously proposed incremental network expansion and use the A∗ search algorithm equipped with suitable heuristic functions. We also discuss the design and correctness of our algorithm and present experimental results that show the efficiency and effectiveness of our solution. / Uma consulta de vizinhos mais próximos (ou kNN, do inglês k nearest neighbours) recupera o conjunto de k pontos de interesse que são mais próximos a um ponto de consulta, onde a proximidade é computada do ponto de consulta para cada ponto de interesse. Nas redes de rodovias tradicionais (estáticas) o custo de deslocamento de um ponto a outro é dado pela distância física entre esses dois pontos. Por outro lado, nas redes dependentes do tempo o custo de deslocamento (ou seja, o tempo de viagem) entre dois pontos varia de acordo com o instante de partida. Nessas redes, as consultas kNN são denominadas TD-kNN (do inglês Time-Dependent kNN). As redes de rodovias dependentes do tempo representam de forma mais adequada algumas situações reais, como, por exemplo, o deslocamento em grandes centros urbanos, onde o tempo para se deslocar de um ponto a outro durante os horários de pico, quando o tráfego é intenso e as ruas estão congestionadas, é muito maior do que em horários normais. Neste contexto, uma consulta típica consiste em descobrir os k restaurantes (pontos de interesse) mais próximos de um determinado cliente (ponto de consulta) caso este inicie o seu deslocamento ao meio dia. Nesta dissertação nós estudamos o problema de processar uma variação de consulta de vizinhos mais próximos em redes viárias dependentes do tempo. Diferentemente das consultas TD-kNN, onde a proximidade é calculada do ponto de consulta para um determinado ponto de interesse, estamos interessados em situações onde a proximidade deve ser calculada de um ponto de interesse para o ponto de consulta. Neste caso, uma consulta típica consiste em descobrir os k taxistas (pontos de interesse) mais próximos (ou seja, com o menor tempo de viagem) de um determinado cliente (ponto de consulta) caso eles iniciem o seu deslocamento até o referido cliente ao meio dia. Desta forma, nos cenários investigados nesta dissertação, são os pontos de interesse que se deslocam até o ponto de consulta, e não o contrário. O método proposto para executar este tipo de consulta aplica uma busca A∗ à medida que vai, de maneira incremental, explorando a rede. O objetivo do método é reduzir o percentual da rede avaliado na busca. A construção e a corretude do método são discutidas e são apresentados resultados experimentais com dados reais e sintéticos que mostram a eficiência da solução proposta.