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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
261

Boundary and material in structural optimization. / CUHK electronic theses & dissertations collection

January 2007 (has links)
Boundary variation method and material distribution method are distinct approaches for structural optimization. In the early days, due to the fact that boundary variation methods were generally not able to handle topological changes, it was applied only in shape optimization problems where the topology of initial design is fixed during optimization process. To enable topological changes that are essential to deliver major performance improvements, material distribution method was introduced in the work of Bendsoe and Kikuchi, and thereafter widely adopted in nearly all aspects of topology optimization. Recently a novel boundary variation method for topology optimization was developed based on level set method, in which topological changes is allowed for. In the thesis, we study the level set based boundary variation method and material distribution method for structure optimization problem. / Finally, we studied the semi-Lagrange scheme to solve the Hamilton-Jacobi equation in level set based boundary variation method. In level set method, the free boundary of a structure is optimized via solution of a Hamilton-Jacobi equation. The numerical stability condition in explicit schemes for discrete Hamilton-Jacobi equation severely restricts the time step. To improve the numerical efficiency, we employ a semi-Lagrange scheme to solve Hamilton-Jacobi equation. Therefore, much larger time steps can be obtained and the number of iterations before convergence is greatly reduced. / Firstly, we studied the minimum compliance optimization problem of thermoelastic structures. In this optimization problem, we find that the optimal structures given by the state-of-art material distribution method, SIMP i method, generally have large area of intermediate density values that are not feasible in practical engineering applications because of their poor manufacturability and high costs. Therefore, we apply level set based boundary variation method in the optimization problem. As numerical results show, the optimal structures obtained are well suited to engineering applications. / To sum up, we explore in this thesis the boundary variation method and material distribution method for structure optimization problem. Several meaningful results and conclusions are obtained. / We secondly studied the stress minimization problem. In practical applications the most important requirement on a structure is often the strength of structure which characterizes the resistance to failure. In stress minimization problem, the objective is to minimize the distribution of von Mises stress in a structure. Here, level set method gives a significant convenience for stress optimization, in particular, we need not to incorporate any stress amplification factor of material microstructure which would be an important issue in material distribution method. Moreover, in order to derive more control of maximum stress, we utilize the Kreisselmeier-Steinhauser function to aggregate stresses at each point in a structure into a single global function. / Xia, Qi. / "October 2007." / Adviser: Michael Yu Wang. / Source: Dissertation Abstracts International, Volume: 69-08, Section: B, page: 4993. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 102-111). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.
262

Earthquake distributions at volcanoes : models and field observations

Roberts, Nick Stuart January 2016 (has links)
Volcanic earthquakes can provide significant insight into physical processes acting at volcanoes, such as magma accumulation and the mechanisms of deformation of the volcanic edifice. At the same time a statistical analyses of volcanic seismicity prior to an eruption (for example variations in the Gutenberg-Richter b-value – a measure of the proportion of large and small events) are a key component of the practical problem of forecasting eruptions. This thesis aims to tackle two key areas of research that are closely related to these important overall goals, by comparing seismic data obtained from currently-active volcanoes with direct field observation of faulting and fracturing from an exhumed extinct volcano. First I introduce a new approach that improves the accuracy and reliability of calculating spatial and temporal variations of the seismic b-value for frequency-magnitude distributions at active volcanoes, and apply it to several test cases. An extensive literature review highlights a large variability and lack of standardisation of methodology used to analyse frequency-magnitude distributions in the past. Motivated by this, I introduce and test a new workflow to standardise calculating completeness magnitudes of seismic catalogues. The review also highlights the fact that uncertainties in estimating the threshold magnitude of complete reporting have been ignored to date. Here I use synthetic catalogues to quantify this previously unidentified source of error, and provide a template to estimate the total error in b-value. In standard analysis it is also common to sample time windows subjectively, although this can introduce bias. Here I develop a new objective, iterative sampling method that calculates the b-value as a full probability density function which need not have a Gaussian error structure. Application of this method reveals ‘mode-switching’ behaviour for the first time in volcanic seismic catalogues. The results also show b-values often do have a value indistinguishable from that of tectonic seismicity (b=1 within error). Nevertheless there are also several robust examples of real high b-values, as high as 3.3. The second part of the study is based on a field campaign to investigate the fracture zones from an exhumed volcanic setting on the Isle of Rum, NW Scotland. Lithological and structural mapping is used to collect structural data that is then used to quantify and explain complex fracture patterns and the underlying intra-magma chamber processes that occurred there in the geological past. In particular I identify a singular collapse event within the youngest volcanic unit, the Central Intrusion. This is responsible for forming the observed igneous breccias and the lineaments on satellite images that I interpret as contemporaneous faults. Using appropriate scaling relations, I infer the b-value for the Rum lineaments data. This would have been relatively high, at a value of approximately 1.9. The final part of the study compares the fracture data on Rum to earthquake distributions at El Hierro volcano, Canary Islands. Here I show the level of fractal clustering is similar in both an extinct (60 Ma) and a currently active volcano. Both show similar high levels of clustering. However, in both cases there is a difference between the capacity and correlation dimensions (D₀≠D₂), implying the set of rupture sources or mapped fault traces form a multi-fractal set. Broadly, the scaling of fracture sets in an ancient volcano has similar properties to those observed in a modern volcano, except that the Rum data imply a greater absolute degree of spatial clustering of deformation than that for the recent unrest at El Hierro.
263

Location Value of Milk

Beutler, Martin K. 01 May 1981 (has links)
Due to the growth of milk marketing areas in the Intermountain West, a study was made to determine the most advantageous allocation of producer milk to twelve selected processing demand areas and to calculate location differentials between these same markets. A theoretical determination of location differentials and of the allocation of milk supply areas to processing centers were made using supply-push and demand-pull price alignment models developed by Associated Milk Producers, Inc., for the months of November 1979 and June 1980. Grade A producer mil k from the six member cooperatives of Western Dairymen' s Cooperative, Inc., was used in the study. From the computed location differentials, a framework was developed from which milk cooperatives in the Intermountain West could use to base future policy decisions.
264

The effect of cooking method upon iron and zinc bioavailability in rice

Shahnaseri, Mahnaz, University of Western Sydney, Hawkesbury, Faculty of Science, Technology and Environment, School of Food Science January 2001 (has links)
Prevention of iron deficiency rather than treatment is preferred by most nutritionists. The presence of a maximal iron supply is not advised because an excessive or unnecessary iron supplement may have biologically adverse effects, such as impaired immune resistance or negative interaction with other trace elements. All cereals and most vegetables contain phytate (inositol hexaphosphate) which can bind iron and zinc and reduce their biological availability. The amount of iron available for absorption in any given diet depends to a large extent on the composition of the diet, e.g., the presence of vitamin C and haem iron, and the absence of phytate. Rice is one of the most important staples in the Iranian diet and, in fact, rice, for most Iranians, is not a side dish but a main dish to which other foods or ingredients are added. An awareness of the effects of cooking method on nutrient content is important because cooking techniques influence the overall quality of a group's diet. The goal of this study is to determine the bioavailability of iron and zinc in traditional Iranian rice dishes and to assess the effect of traditional methods of cooking rice upon iron and zinc bioavailability. Iranian migrants residing in Sydney were surveyed in order to determine their food habits and traditional cooking methods, for the assessment of their effects upon the bioavailability of iron and zinc in Iranian rice dishes. Rice contains phytate, which is a potent inhibitor of iron absorption. The amount of phytate in rice depends on whether the rice is polished or not. The pre-cooking treatment such as soaking can also influence the phytate content of the rice. Soaking prior to cooking also reduced the amount of ion and zinc. The inhibitory effect of phytate is also overcome by adding different herbs, vegetables and legumes used traditionally in rice dishes cooked by Iranians. Herbs or vegetables such as coriander, parsley and cauliflower, used in Iranian rice dishes, increased the bioavailability iron and zinc. Results obtained from this research show that method of cooking, as well as the food mixture, is very important for the absorption of iron and zinc from the diet / Doctor of Philosophy (PhD)
265

An improved convexity maximum principle and some applications

Kennington, Alan U. January 1984 (has links) (PDF)
Typescript (Photocopy) Bibliography: leaf 75.
266

EVA - Ett helhetskoncept eller komplement?

Glamstedt, Jennie, Sigbo, Marie January 2008 (has links)
<p>Alla företag strävar efter att göra en vinst, men frågan är när ett företag faktiskt uppnått detta. </p><p>Stern Stewart & Co är ett amerikanskt konsultbolag som har arbetat fram ett koncept som de kallar Economic Value Added (EVA). Den stora skillnaden mellan detta och övriga vinstmått är att EVA visar att ingen vinst har uppnåtts förrän även kostnaderna för det egna kapitalet, d.v.s. den avkastning som aktieägarna förväntar sig, är täckta. Stern Stewart & Co har marknadsfört EVA som ett helhetskoncept som ska användas för styrning i hela företaget. Den fråga som vi har ställt oss är hur EVA-konceptet ser ut i svenska företag. Syftet med studien är att beskriva EVA-konceptets användningsområden och förklara hur svenska företag arbetar med måttet. För att besvara frågan och uppfylla syftet krävdes en helhetsförståelse över företagens situation, därför har en kvalitativ ansats använts. Undersökningen består av intervjuer som genomförts med fyra företag som använder sig av EVA-konceptet. De resultat vi har fått fram visar att företag anpassar modellen efter sina behov och förutsättningar samt att den används som ett komplement eller kompletteras av andra mått. Vidare har införandet av EVA-konceptet inte någon förankring i att företag vill arbeta mer mot aktieägarnas intressen, utan att syftet med att använda EVA-konceptet har andra skäl.</p>
267

Risk Management based on GARCH and Non-parametric stochastic volatility models and some cases of Generalized Hyperbolic distribution

Midov, Askerbi, Balashov, Konstantin January 2008 (has links)
<p>The paper is devoted to the modern methods of Value-at-Risk calculation using different cases of Generalized Hyperbolic distribution and models for predicting volatility. In our research we use GARCH-M and Non-parametric volatility models and compare Value-at-Risk calculation depending on the distribution that is used. In the case of Non-parametric model corresponding windows are proved by the Cross Validation method. Furthermore in our work we consider adaption of the method to intraday data using ACD and UHF-GARCH models. The project involves also application of the developed methods to real financial data and comparable analysis of the obtained results.</p>
268

E-HEALTH – THE USAGE OF ICT DEVELOPING HEALTH CARE SYSTEM : MULTIPLE-CASE STUDY OF EUROPEAN COUTRIES DENMARK AND LITHUANIA

Kurtinaityte, Laura January 2007 (has links)
<p>Electronic health – this is the object of study work. The focus of research is European countries, which use Information and Communication Technologies improving their Health care system and it is not excepted is the country advanced in developing e-Health or it just started to create or improve this system. As it is a new Developing research area, there are not so many direct relevant researches about it previously found. Therefore it encourages the investigation of this topic, which according to European Commission and Enterprise Directorate General (2003) could reach greatest economy on saving costs in whole service sector. Thus the guidelines for efficient e-Health development should be given as soon as possible. The study work is exactly aimed on this.</p>
269

Initial and boundary value problem for a third order differential equation of parabolic type /

Al-Ayat, Rokaya A. January 1970 (has links)
Thesis (Ph. D.)--Oregon State University, 1970. / Typescript (photocopy). Includes bibliographical references (leaves 90-91). Also available on the World Wide Web.
270

Uniqueness implies uniqueness and existence for nonlocal boundary value problems for fourth order differential equations

Ma, Ding. Henderson, Johnny. January 2005 (has links)
Thesis (Ph.D.)--Baylor University, 2005. / Includes bibliographical references (p. 54-58).

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