Global warming and air pollution are the major problems facing the world today. Therefore strict environmental legislation on the emission of harmful gases from motor vehicles has forced the automobile industry to search for alternative materials or new materials for exhaust systems. In order to produce cleaner exhaust gases, the exhaust temperature needs to be increased to approximately 900oC. Therefore, exhaust manifolds are exposed repeatedly to hot gases as they are nearest to the engine requiring good oxidation resistance, thermal fatigue properties, cold workability and weldability. One such material to meet the above characteristics is AISI 441 ferritic stainless steel, a dual stabilised Ti and Nb ferritic stainless steel. Ti and Nb are added to stainless steel to stabilise C and N due to their high tendency to form carbonitrides (Ti,Nb)(C,N) and laves phase (Fe2Nb) and Fe3Nb3C. With 18% Cr content, this steel has a good corrosion resistance at elevated temperatures. Included in many applications of this steel are those requiring deep drawing and related forming operations. However, the drawability and stretchability of ferritic stainless steels is inferior to that of the more expensive austenitic stainless steels. For instance, Columbus Stainless has experienced ridging/roping problems at times during the manufacturing process of type AISI 441 ferritic stainless steel. It is believed that this problem is related to crystallographic texture of materials which have effect on formability. The R-value in FSS can be improved through optimisation of chemical composition, which includes reducing the carbon content, and processing conditions such as reducing the slab reheating temperature, increasing annealing temperature and refining the hot band grain size. Therefore the aim of this research project was firstly to investigate effect of amount of cold reduction and annealing temperature on texture evolution and its influence on formability. The as received 4.5 mm hot band steel was cold rolled by 62, 78 and 82% reductions respectively followed by isothermal annealing of each at 900oC, 950oC and 1025oC for 3 minutes. Orientation distribution function (ODF) through X-ray diffractometer (XRD) measurement was used to characterise the crystallographic texture formed in the steel using PANanalytical X’Pert PRO diffractrometer with X’celerator detector and variable divergence. Microstructures were characterised using optical microscopy and scanning electron microscope (SEM). The results show that steels that received 78% cold reduction and annealed at 1025oC recorded the highest Rm-value and lowest ΔR-value which enhances its deep drawing capability. In addition, this steel showed the highest intensity of shifted γ-fibre, notably {554}<225> and {334}<483>. It can therefore be concluded that the γ-fibre which favours deep drawing, is optimal after 78% cold reduction and annealing at 1025oC. The second objective was to investigate the effect of (Nb+Ti) content on the crystallographic texture and the subsequent formability and ridging severity. AISI 441 ferritic stainless steel with different amount of (Nb+Ti) content was used i.e. Steel A (0.26Nb+0.2Ti), Steel B (0.44Nb+0.15Ti) and steel C (0.7Nb+0.32Ti). After a strain of 10%, steels A exhibited the least resistance against surface ridging with average roughness Ra of 1.5 μm followed by steels B with an average roughness Ra of 1.1μm. Steel C showed the highest resistance to ridging with an average roughness Ra of 0.64 μm. This was attributed to the increase in carbonitrites (NbTi)(C,N) due to increased (Nb+Ti) content which acted as nucleation sites for γ-fibre. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Materials Science and Metallurgical Engineering / unrestricted

Die vorliegende Arbeit befasst sich mit dem Versuch der Optimierung von Simulated Annealing. Genauer gesagt, werden Simulationsergebnisse für einfache Spinglassysteme in Abhängigkeit von verschiedenen Nachbarschaftsmodellen berechnet – jeweils unter Verwendung des optimalen Abkühlverlaufs. Ziel ist es, eine Faustregel für die dynamische Anpassung der Nachbarschaftsbeziehung während einer Annealing-Simulation zu finden. / The thesis at hand presents an attempt to optimize simulated annealing. In particular, annealing results are computed based on different move class definitions for Ising spin systems while simultaneously applying an existing algorithm to determine the optimal temperature schedule for each case. The aim is to find a rule of thumb for dynamic adjustment of the move class during an annealing run.

Silicon carbide (SiC), is a wide band gap (2.4 eV < Eg < 3.3 eV) semiconducting material well known for its potential applications in high-temperature, high-power, high-frequency or hard radiation resistant devices. In this thesis, we are broadening elementary knowledge about this material. We identify energy levels in the material, using Photo-Hall effect spectroscopy supported by the temperature dependency of classic Hall effect measurement and temperature dependent photoluminescence. This knowledge is essential to allow SiC application as a radiation detector.

2D semiconductors are one of the most promising materials for next-generation electronics. Realizing continuous 2D monolayer semiconductors with single-crystalline structure at the wafer scale is still a challenge. We developed an epitaxial phase conversion (EPC) process to meet these requirements. The EPC process is a two-step process, where the sulfurization process was carried out on pre-deposited Mo-containing films. Traditionally, two-step processes for 2D MoS2 and other chalcogenides have suffered low-quality film and non-discontinuity at monolayer thickness. The reason was regarded as the low lattice quality of precursor film. The EPC process solves these problems by carefully preparing the precursor film and carefully controlling the sulfurization process. The precursor film in the EPC process is epitaxial MoO2 grown on 2″ diameter sapphire substrate by pulsed laser deposition. This epitaxial precursor contains significantly fewer defects compared to amorphous precursor films. Thus fewer defects are inherited by the EPC MoS2 film. Therefore, EPC MoS2 film quality is much better. The EPC prepared monolayer MoS2 devices to show field-effect mobility between 10 ~ 30 cm2·V-1s-1, which is the best among the two-step process. We also developed a CLAP method further to reduce the defects in the precursor oxide film; thus, in-plane texture in the thicker MoS2 film was eliminated, and a single-crystalline structure was obtained in the wafer-scale MoS2 films. The potentially feasible technique to further improve the 2D film quality is pointed out for our next research plan. Meanwhile, the epitaxial phase conversion process was proposed to be as a universal growth method. Last but not least, we demonstrate several potential applications of the wafer-scale single-crystalline MoS2 film we developed, such as logic circuits, flexible electronics, and seeding layer of van der Waal or remote epitaxial growth.

Procedural level generation is a novel area of research within the field of computer graphics and game development. However, current research and implementations of procedural generation for cooperative games is sparse. Further study is required to validate the use of automatic level creation and to test additional methods of optimization for cooperative games. Additionally, despite many recent developments, many areas within the field of virtual reality remain underexplored. We propose a mathematically defined total cost function for controlling a procedural level generation algorithm for cooperative virtual reality games. This cost term controls an algorithm which gradually improves a generated solution over a series of iterations, bringing it to an optimal state. We present here two games with procedurally created levels and gameplay elements using this mathematical total cost function, as well as proposed experiments to validate the effectiveness of this content in encouraging cooperation and potential use cases for this technology.

Stainless steel family grades are very famous for their combined corrosion resistance and high mechanical properties. These properties can be improved further by decreasing the content of impurities like carbon and oxygen. The main purpose of this research work is to study the possibility of stainless steel powder decarburization by vacuum annealing. The influence of different process parameters like treatment time, temperature, fraction size and depth of the powder layer on the decarburization process was analyzed. The investigation results showed that it is possible to achieve extra low values of carbon and oxygen in steel powder by processing it with optimum process parameters.

Thesis: B.S., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1980 / Includes bibliographical references. / by Evan Joseph Hammerman. / B.S. / B.S. Massachusetts Institute of Technology, Department of Materials Science and Engineering

The university timetabling problem is an NP-complete problem which schools all over the world face every semester. The aim of the problem is to schedule sets of events such as lectures and seminars into certain time slots without violating numerous specified constraints. This study aimed to automate this process with the help of simulated annealing and compare the results with a genetic algorithm. The input data sets were inspired by the Royal Institute of Technology in Stockholm. The results showed a great run time difference between the two algorithms where the simulated annealing performed much better. They also showed that even though the simulated annealing algorithm was better during all stages, the genetic algorithm had a much better performance in early stages than it had in latter. This led to the conclusion that a more optimized, hybrid algorithm could be created from the two algorithms provided that the genetic algorithm could benefit from the improvements suggested in previous research. / Universitetsschemaläggningsproblemet är ett NP-fullständigt problem som skolor över hela världen måste hantera innan varje termin. Syftet med problemet är att schemalägga händelser, såsom föreläsningar och seminarier, utan att bryta flertalet fördefinierade villkor. Denna studie hade som mål att automatisera denna process med hjälp av algoritmkonstuktionsmetoden simulerad glödgning och sedan jämföra resultatet med en genetisk algoritm. De datamängder som användes är inspirerade av den verkliga situationen på KTH. Resultaten visar stora tidsmässiga skillnader där algoritmen baserad på simulerad glödgning går snabbare. De visar dock också att den genetiska algoritmen har en bättre prestanda i tidigare stadier än i senare. Detta ledde till slutsatsen att en mer optimerad hybridalgoritm kan skapas av de två algoritmerna, förutsatt att den genetiska algoritmen kan dra nytta av förbättringar som föreslagits i tidigare forskning.

A growing world population means an increase in crop demand. At the same time climate change threatens food security as crops may become maladapted to a new environment. We need to adapt crops to increase crop yield and become resistant to a changed environment to meet this. Crop wild relatives (CWR), which have a genetic relatedness with our crops, will be of importance as a genetic resource for crop adaption and needs to be protected. Vaccinium myrtillus is one of the prioritized species on the Nordic countries CWR priority list. Here I report PCR protocols that can be used for amplifying microsatellites, or SSRs, within V. myrtillus for use in analyses of genetic diversity within and between populations. PCRs with varying annealing temperatures (Ta) were performed. An optimal Ta for the primer pair was found for four SSR loci, and for four SSR loci, an approved Ta was found. These eight primer pairs can be used to amplify SSRs for analyses of the genetic diversity between V. myrtillus populations. This is needed to evaluate which populations to focus on in conservation programmes to ensure a broad genetic diversity usable in crop adaptation to meet increasing crop demand and climate change.

This dissertation is concerned with the unconstrained global optimization of nonlinear problems. These problems are not easy to solve because of the multiplicity of local and global minima. In this dissertation, we first study the pattern search method for local optimization. We study the pattern search method numerically and provide a modification to it. In particular, we design a new pattern search method for local optimization. The new pattern search improves the efficiency and reliability of the original pattern search method. We then designed two simulated annealing algorithms for global optimization based on the basic features of pattern search. The new methods are therefore hybrid. The first hybrid method is the hybrid of simulated annealing and pattern search. This method is denoted by MSA. The second hybrid method is a combination of MSA and the multi-level single linkage method. This method is denoted by SAPS. The performance of MSA and SAPS are reported through extensive experiments on 50 test problems. Results indicate that the new hybrids are efficient and reliable.