THE EVACUATION PROBLEM IN MULTI-STORY BUILDINGS

The pressure from high population density leads to the creation of high-rise structures within urban areas. Consequently, the design of facilities which confront the challenges of emergency evacuation from high-rise buildings become a complex concern. This paper proposes an embedded program which combines a deterministic (GMAFLAD) and stochastic model (M/G/C/C State Dependent Queueing model) into one program, GMAF_MGCC, to solve an evacuation problem. An evacuation problem belongs to Quadratic Assignment Problem (QAP) class which will be formulated as a Quadratic Set Packing model (QSP) including the random flow out of the building and the random pairwise traffic flow among activities. The procedure starts with solving the QSP model to find all potential optimal layouts for the problem. Then, the stochastic model calculates an evacuation time of each solution which is the primary decision variable to figure the best design for the building. Here we also discuss relevant topics to the new program including the computational accuracy and the correlation between a successful rate of solving and problems’ scale. This thesis examines the relationship of independent variables including arrival rate, population and a number of stories with the dependent variable, evacuation time. Finally, the study also analyzes the probability distribution of an evacuation time for a wide range of problem scale

Development of a Wide Bandwidth Array Acousto-Optical Spectrometer for the Herschel Satellite Mission

The Herschel satellite observatory will explore the universe at far-infrared, submillimetre, and millimetre wavelengths. This regime of the electromagnetic spectrum is difficult to observe, because water vapour in the Earth's atmosphere absorbs the signals of almost all the astronomical sources. With the 3.5m telescope (the largest ever placed aboard a spacecraft), it will be possible to observe various atomic and molecular lines with exceptionally high spatial resolution. The receiver system employs the heterodyne technique, and the spectral information is obtained by means of real-time spectrometers. Within this thesis, the requirements, specifications, design concept, and development of a wide bandwidth array acousto-optical spectrometer (WBS) is discussed. Both ground-based and satellite applications have demonstrated that acousto-optical spectrometers (AOS) utilize a reliable signal-processing technique. For the Herschel mission, the spectrometers demand a large frequency bandwidth and high resolution. These are achieved by means of hybrid technology. This means that the signal is split into four sub-bands and analyzed by using a four-channel array Bragg cell. The spectra of the four individual channels are co-added by software to create the complete wide bandwidth spectrum of the input signal. Since the channels of the deflector are illuminated by a semi-conductor laser that provides relatively low optical power, the imaging optical system requires careful design to make the instrument efficient. In comparison with earlier AOSs, the Herschel WBS has outstanding optical efficiency due to its diffraction-limited and efficiency-optimized optical design. The first part of the optics that illuminates the Bragg cell (Laser Source Module) comprises two laser diodes (the second laser is needed for redundancy reasons), the collimation and imaging optics, and the specially-designed beam splitter. The great advantage of the prism-based beam splitter design is that it generates the four beams necessary for the illumination of the deflector and makes it possible to couple the light of the redundant laser without applying an additional beam splitter, which would significantly reduce the efficiency of the instrument. The second part of optics images the deflected light of the Bragg cell onto a four-line linear CCD detector. The design of the diffraction limited lens system makes it possible to achieve the required high resolution and high efficiency. At the same time, the optimization of the optical efficiency affects the mechanical and thermal sensitivity of the spectrometer. Since the high mechanical stability is an important concern for the spectroscopic stability performance of the instrument, it is essential to use materials that have high stiffness and low thermal expansion. Specifically, the mounting of the laser diode requires a thermally compensated design to reduce the deformations caused by thermal changes. In addition to the high stiffness, the weight of satellite-borne instruments must be minimized. Thus, most of the components are light weighted and made of a special aluminium alloy. The imaging optical system of the spectrometer is designed to be diffraction limited. However, the deflector considerably reduces the resolution, since it has a small aperture, and the acousto-optical material has poor optical quality. For the first time, theoretical investigations of the resolution involving the Bragg cell were carried out. The diffraction phenomenon of the acoustic aperture of the Bragg cell is studied by using the Fraunhofer diffraction theory. The model of the deflector includes the frequency-dependent dimension of the acoustic zone and the attenuation of the acousto-optical material. Furthermore, the model makes it possible to explore the impact of the illuminating laser beam position change relative to the active zone of the Bragg cell on the resolution of the spectrometer. For investigations of alignment errors, this is of particular importance. An additional highlight of this theoretical investigation is that lens aberration errors and crystal imperfections that adversely affect the wavefront aberration, i.e. the resolution, can be also examined by diffraction analysis. As part of the qualification procedure, thorough thermal, deformation, and resonance investigations are made with the spectrometer assembled with dummy loads. During the development phase, the early tests of mechanical deformations caused by thermal variations show the mechanical stability and thermal sensitivity of the instrument and therefore provide detailed information for further optical and mechanical development phases. Further resonance search tests are conducted to measure the mechanical stability of the unit. The power and frequency stability of the spectrometer is partly dependent on the performance of the laser diode and the stability of its power supply. Thus, the laser diodes selected from the batch of the flight lasers were investigated to determine their single mode behaviour, mode jump characteristics, wavelength hysteresis, and wavelength stability. Because the laser light feedback from the surfaces of the collimating optics might also appreciably reduce the power stability of the instrument, investigations are performed with the special collimator design of the WBS. In order to determine the reliability of the lasers, accelerated lifetime tests are performed, and conclusions are drawn relating to lifetime statistics. The WBS must meet strict performance standards before it can be flown on Herschel. The space-qualification procedure comprises diverse tests that simulate the extreme environment of the spectrometer in orbit. The results of these tests indicate the quality of the mechanical and optical design and confirm the adjustment precision of the instrument. Within the operating temperature range of the spectrometer, the efficiency, bandpass, and resolution variations are characterized. Moreover, the noise performance is investigated in detail. For prolonged astronomical measurements it is of crucial importance that the backend system does not significantly contribute to the radiometric noise. Due to the meticulous design of the WBS, the outstanding noise performance makes it possible to efficiently perform integrations of hundreds of seconds. All these tests indicate that the array acousto-optical spectrometer designed for the Herschel satellite will operate successfully

Multifacility location with imprecise data

Ankara : The Department of Industrial Engineering and the Institute of Engineering and Science, Bilkent Univ., 1994.Thesis (Master's) -- Bilkent University, 1994.Includes bibliographical references leaves 75-78.Locational decisions often suffer from lack of precise data. In this study, we consider a class of multifacility location problems where the demands of existing and new facilities are unknown, with a known set of possible realizations. The set may be finite or infinite. In the latter case, the data is assumed to be of interval type. We use various criteria to evaluate candidate solutions to these problems and build a framework for decision making.Demir, Muhittin HakanM.S

A review of network location theory and models

Cataloged from PDF version of article.In this study, we review the existing literature on network location problems. The study has a broad scope that includes problems featuring desirable and undesirable facilities, point facilities and extensive facilities, monopolistic and competitive markets, and single or multiple objectives. Deterministic and stochastic models as well as robust models are covered. Demand data aggregation is also discussed. More than 500 papers in this area are reviewed and critical issues, research directions, and problem extensions are emphasized.Erdoğan, Damla SelinM.S

Theoretical and experimental approaches for the initiation and propagation of activity in spatially embedded neuronal cultures

[eng] Spatial embedding and inherited metric constraints are a fundamental trait of biological neuronal circuits. However their role in shaping connectivity and dynamics has been often disregarded, with models of neuronal networks paying much more attention to the distribution of connections in the quest for understanding network's behavior. In this thesis we aim at filling this gap by studying the importance of metric features in the complex connectivity- dynamics-noise interplay that shapes spontaneous neuronal activity. This thesis combines experiments in rat dissociated neuronal cultures with theoretical analyses to better comprehend the relevance of spatial embedding. We developed a new theoretical model grounded on Ising Models to assess metric effects in neuronal cultures' behavior, and in the context of percolation approaches. Once metric effects were settled, we illustrated their relevance in shaping spontaneous activity by perturbing the structural connectivity blueprint of neuronal cultures. This was achieved by patterning the substrate where neurons grow, and by using topographical molds that dictated the connectivity of the network. Next, and since the initiation of bursting activity is governed in great manner by a complex amplification mechanism that involves metric correlations and noise, we focused on the metric-driven amplification of spontaneous single-neuron noise to derive an analytical model that predicts the frequency of bursting events in neuronal cultures. We then further investigated in an experimental context the contribution of noise to the observed activity patterns, and by implementing a moderate electrical stimulation protocol that increases the level of activity noise in cultures. Finally, the latter study was completed with experiments regarding the specific role of inhibition in neuronal networks, to provide a wider understanding of the mechanisms that govern the initiation and propagation of activity fronts in cortical cultures.[cat] L'objectiu d'aquesta tesis és investigar els mecanismes que generen l'activitat espontània i estimulada en xarxes neuronals, més concretament en cultius corticals dissociats, i fent un especial èmfasi en l’efecte de les correlacions mètriques. En aquest marc, l’activitat col·lectiva consisteix en episodis esporàdics de dispars quasi sincronitzats entre totes les neurones del cultiu, anomenats “esclats de xarxa”. Tres elements principals en determinen les característiques: connectivitat entre neurones, dinàmica intrínseca neuronal, i soroll (activacions neuronals aleatòries). La investigació s’ha centrat en cinc línies de recerca: l’estudi de correlacions mètriques en cultius neuronals; el desenvolupament d’un model teòric per descriure i predir l’esclat de xarxa; l’anàlisi de la propagació dels fronts d’activitat experimentals sota pertorbacions estructurals de la connectivitat del cultiu; l’estudi de l’efecte de la inhibició en la iniciació i propagació dels esclats ‘in vitro’; i l’estudi de la resposta experimental dels cultius sota una estimulació elèctrica moderada de baixa freqüència. En la primera línia de recerca hem comprovat que les correlacions mètriques dominen el comportament dinàmic del cultiu, fins al punt d’emmascarar la contribució de la distribució del nombre de connexions. En la segona línia hem desenvolupat un model analític que prediu semi- quantitativament la freqüència dels esclats observada experimentalment. La tercera línia s’ha centrat en l’efecte de pertorbacions estructurals en la connectivitat; la dinàmica resultant ha mostrat una gran riquesa en patrons d’activitat, esclats de xarxa a diferents escales, i propagació altament específica de cada cultiu. La quarta línia de recerca ha demostrat que les xarxes sense inhibició disminueixen la seva freqüència d’esclat respecte a les xarxes control, que la velocitat de propagació de l’activitat incrementa lleugerament quan s’ha bloquejat la inhibició, i que els punts on s’inicien ens esclats varien respecte als controls. I, finalment, la cinquena línia de recerca ha constatat que l’aplicació d’un camp elèctric feble augmenta el soroll d’activitat de la xarxa, generant un increment en la freqüència dels esclats de xarxa

Parallel algorithms for direct blood flow simulations

Fluid mechanics of blood can be well approximated by a mixture model of a Newtonian fluid and deformable particles representing the red blood cells. Experimental and theoretical evidence suggests that the deformation and rheology of red blood cells is similar to that of phospholipid vesicles. Vesicles and red blood cells are both area preserving closed membranes that resist bending. Beyond red blood cells, vesicles can be used to investigate the behavior of cell membranes, intracellular organelles, and viral particles. Given the importance of vesicle flows, in this thesis we focus in efficient numerical methods for such problems: we present computationally scalable algorithms for the simulation of dilute suspension of deformable vesicles in two and three dimensions. Our method is based on the boundary integral formulation of Stokes flow. We present new schemes for simulating the three-dimensional hydrodynamic interactions of large number of vesicles with viscosity contrast. The algorithms incorporate a stable time-stepping scheme, high-order spatiotemporal discretizations, spectral preconditioners, and a reparametrization scheme capable of resolving extreme mesh distortions in dynamic simulations. The associated linear systems are solved in optimal time using spectral preconditioners. The highlights of our numerical scheme are that (i) the physics of vesicles is faithfully represented by using nonlinear solid mechanics to capture the deformations of each cell, (ii) the long-range, N-body, hydrodynamic interactions between vesicles are accurately resolved using the fast multipole method (FMM), and (iii) our time stepping scheme is unconditionally stable for the flow of single and multiple vesicles with viscosity contrast and its computational cost-per-simulation-unit-time is comparable to or less than that of an explicit scheme. We report scaling of our algorithms to simulations with millions of vesicles on thousands of computational cores.PhDCommittee Chair: Biros, George; Committee Member: Alben, Silas; Committee Member: Fernandez-Nieves, Alberto; Committee Member: Hu, David; Committee Member: Vuduc, Richar