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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.
61

First Principle Calculation with Interpolating Scaling Function on Adaptive Gridding

Wang, Jen-chung 09 August 2007 (has links)
A new multiresolution scheme based on interpolating scaling function(ISF) on adaptive gridding(AG) shows promising in the first principle calculation. We also use ISFs on solving Poisson equation(PE), and find good approximations on the expansions of the second derivatives of ISFs. It is simpler than the wavelet scheme and fully implements the fast wavelet transformation so that the method is very suitable to problems with frequently updating charge density such as the first-principle calculation in electronic structures in atoms, molecules, and solids. Although the scheme is similar to the AG scheme on real space, the ISFs can represent fields more effectively and it needs less grids than the scheme of real space does. This simple and effective method provides an alternative to both the real space and the wavelet methods in the first principle calculation. Also, The method can be easily parallelized due to the block structure of the grid layout.
62

Continued Radicals and Cantor Sets

Clark, Thomas Tyler 01 May 2012 (has links)
We examine the formation of sets homeomorphic to the ternary Cantor set by continued radicals. We determine properties of bridges and gaps and calculate the thickness of the Cantor set. From this we apply information from continued fractions to continued radicals to obtain new results. We also consider the measure of several Cantor sets.
63

微小重力下での直線燃料液滴列に沿った火炎伝ぱ (第3報, 火炎伝ぱのモデル計算)

梅村, 章, UMEMURA, Akira, 内田, 正宏, UCHIDA, Masahiro 09 1900 (has links)
No description available.
64

Thermoelectric properties of transition metal oxides and thallium main group chalcogenides

Jianxiao, Xu January 2008 (has links)
Thermoelectric energy (TE) conversion can be used to create electricity from temperature gradients. Hence power can be generated from waste heat using TE materials, e.g. from the exhaust in automotives. This power in turn may lead to a reduction of gas consumption by reducing the alternator load on the engine. Because of the increasing demand and limited availability of energy sources, there is strong and renewed interest in advancing thermoelectric materials. Past research shows that the best TE materials are narrow band gap semiconductors composed of heavy elements, exhibiting a large Seebeck coefficient, S, combined with high electrical conductivity, σ, and low thermal conductivity, κ. Various research projects have been attempted during the past four years of my Ph.D. studies. These include the synthesis, crystal structure studies, electronic structure calculations and thermoelectric properties of transition metal oxides and thallium main group chalcogenides. Because of the good thermal stability, lack of sensitivity to the air, and non-toxicity, transition metal oxides are potential candidates for commercial thermoelectric applications. During the investigation of oxides for thermoelectric application, several interesting features of different transition metal oxides have been discovered: 1. A new quaternary layered transition-metal oxide, Na2Cu2TeO6, has been synthesized under air using stoichiometric mixtures of Na2CO3, CuO and TeO2. Na2Cu2TeO6 crystallizes in a new structure type, monoclinic space group C2/m with a = 5.7059(6) Å, b = 8.6751(9) Å, c = 5.9380(6) Å,  = 113.740(2)°, V = 269.05(5) Å3 and Z = 2, as determined by single crystal X-ray diffraction. The structure is composed of[Cu2TeO6] layers with the Na atoms located in the octahedral voids between the layers. Na2Cu2TeO6 is a green nonmetallic compound, in agreement with the electronic structure calculation and electrical resistance measurement. 2. An n-type narrow band gap semiconductor, LaMo8O14, exhibiting the high Seebeck coefficient of -94 μVK-1 at room temperature has been investigated. 3. Pb0.69Mo4O6 with a new modulated structure and stoichiometry was determined from single-crystal X-ray diffraction data. The compound crystallizes in the tetragonal super space group, P4/mbm(00g)00ss, with a = 9.6112(3) Å, c = 2.8411(1) Å, q = 0.25c*, which is different from the previously reported structure. As for the research of thermoelectric properties of thallium main group chalcogenides, three new ternary thallium selenides, Tl2.35Sb8.65Se14, Tl1.97Sb8.03Se13 and Tl2.04Bi7.96Se13, have been discovered. All three compounds crystallize in the same space group P21/m with different cell parameters, and in part different Wyckoff sites, hence different structure types. The three selenides with similar structures are composed of distorted edge-sharing (Sb,Bi)Se6 octahedra, while the distorted Tl/(Sb, Bi) sites are coordinated by 8 - 9 Se atoms. Electronic structure calculations and physical property measurements reveal they are semiconductors with high Seebeck coefficient but low electrical conductivity, and therefore not good thermoelectrics. On the other hand, our transport property measurements on the unoptimized Tl2SnTe3 sample show interesting thermoelectric properties of this known compound. Advanced thermoelectrics are dominated by antimonides and tellurides so far. The structures of the tellurides are mostly composed of NaCl-related motifs, hence do not contain any Te–Te bonds. All of the antimonide structures containing Sb–Sb bonds of various lengths are much more complex. The Sb atom substructures are Sb24– pairs in β-Zn4Sb3, linear Sb37– units in Yb14MnSb11, planar Sb44– rectangles in the skutterudites, e.g., LaFe3CoSb12, and Sb8 cubes interconnected via short Sb–Sb bonds to a three-dimensional network in Mo3Sb5Te2. The results of electronic structure calculations suggested that these interactions have a significant impact on the band gap size as well as on the effective mass around the Fermi level, which represent vital criteria for advanced thermoelectrics. The crystal structure and electronic structure investigation for the unique T net planar Sb–Sb interactions in Hf5Sb9 will be also presented, although Hf5Sb9 is metallic compound with poor thermoelectric performances.
65

Calculation method based on CASMO/SIMULATE for isotopic concentrations of fuel samples irradiated in Ringhals PWR

Zuwak, Tariq Zuwak January 2012 (has links)
This is a M. Eng. degree project at Uppsala University carried out at Vattenfall NuclearFuel AB. The goal of it is to present a best estimate method based on the code package CASMO/SIMULATE for the purpose of calculating the isotopic concentrations of a specified number of isotopes in a fuel sample. The calculations done with the method shall produce small deviations from reliable measured values, which characterize the accuracy of CASMO/SIMULATE, but also simplicity based onthe computing time and handling of the amount of data is an important factor in the development of the method. The development of the method has been based on a sensitivity calculation with CASMO/SIMULATE on a number of relevant parameters affecting the isotope concentrations. The proposed method has then been applied on three samples irradiated in Ringhals 4 and Ringhals 3. At last the calculated isotopic concentrations have been benchmarked against measured data from Studsvik Laboratory. The sensitivity analyzes has shown that the parameters affecting the neutron moderation are very important for calculating the isotopic concentrations. The core axial resolution is also an important factor for the samples taken from top of the rod,where the power gradient is large. The comparison of the calculated and measured values has shown that SIMULATE, in the analysed cases, simulates a lower finalburnup. This has created a need to correct the final burnup in order to get better results in terms of lower relative deviations between the measured and calculated data.
66

Thermoelectric properties of transition metal oxides and thallium main group chalcogenides

Jianxiao, Xu January 2008 (has links)
Thermoelectric energy (TE) conversion can be used to create electricity from temperature gradients. Hence power can be generated from waste heat using TE materials, e.g. from the exhaust in automotives. This power in turn may lead to a reduction of gas consumption by reducing the alternator load on the engine. Because of the increasing demand and limited availability of energy sources, there is strong and renewed interest in advancing thermoelectric materials. Past research shows that the best TE materials are narrow band gap semiconductors composed of heavy elements, exhibiting a large Seebeck coefficient, S, combined with high electrical conductivity, σ, and low thermal conductivity, κ. Various research projects have been attempted during the past four years of my Ph.D. studies. These include the synthesis, crystal structure studies, electronic structure calculations and thermoelectric properties of transition metal oxides and thallium main group chalcogenides. Because of the good thermal stability, lack of sensitivity to the air, and non-toxicity, transition metal oxides are potential candidates for commercial thermoelectric applications. During the investigation of oxides for thermoelectric application, several interesting features of different transition metal oxides have been discovered: 1. A new quaternary layered transition-metal oxide, Na2Cu2TeO6, has been synthesized under air using stoichiometric mixtures of Na2CO3, CuO and TeO2. Na2Cu2TeO6 crystallizes in a new structure type, monoclinic space group C2/m with a = 5.7059(6) Å, b = 8.6751(9) Å, c = 5.9380(6) Å,  = 113.740(2)°, V = 269.05(5) Å3 and Z = 2, as determined by single crystal X-ray diffraction. The structure is composed of[Cu2TeO6] layers with the Na atoms located in the octahedral voids between the layers. Na2Cu2TeO6 is a green nonmetallic compound, in agreement with the electronic structure calculation and electrical resistance measurement. 2. An n-type narrow band gap semiconductor, LaMo8O14, exhibiting the high Seebeck coefficient of -94 μVK-1 at room temperature has been investigated. 3. Pb0.69Mo4O6 with a new modulated structure and stoichiometry was determined from single-crystal X-ray diffraction data. The compound crystallizes in the tetragonal super space group, P4/mbm(00g)00ss, with a = 9.6112(3) Å, c = 2.8411(1) Å, q = 0.25c*, which is different from the previously reported structure. As for the research of thermoelectric properties of thallium main group chalcogenides, three new ternary thallium selenides, Tl2.35Sb8.65Se14, Tl1.97Sb8.03Se13 and Tl2.04Bi7.96Se13, have been discovered. All three compounds crystallize in the same space group P21/m with different cell parameters, and in part different Wyckoff sites, hence different structure types. The three selenides with similar structures are composed of distorted edge-sharing (Sb,Bi)Se6 octahedra, while the distorted Tl/(Sb, Bi) sites are coordinated by 8 - 9 Se atoms. Electronic structure calculations and physical property measurements reveal they are semiconductors with high Seebeck coefficient but low electrical conductivity, and therefore not good thermoelectrics. On the other hand, our transport property measurements on the unoptimized Tl2SnTe3 sample show interesting thermoelectric properties of this known compound. Advanced thermoelectrics are dominated by antimonides and tellurides so far. The structures of the tellurides are mostly composed of NaCl-related motifs, hence do not contain any Te–Te bonds. All of the antimonide structures containing Sb–Sb bonds of various lengths are much more complex. The Sb atom substructures are Sb24– pairs in β-Zn4Sb3, linear Sb37– units in Yb14MnSb11, planar Sb44– rectangles in the skutterudites, e.g., LaFe3CoSb12, and Sb8 cubes interconnected via short Sb–Sb bonds to a three-dimensional network in Mo3Sb5Te2. The results of electronic structure calculations suggested that these interactions have a significant impact on the band gap size as well as on the effective mass around the Fermi level, which represent vital criteria for advanced thermoelectrics. The crystal structure and electronic structure investigation for the unique T net planar Sb–Sb interactions in Hf5Sb9 will be also presented, although Hf5Sb9 is metallic compound with poor thermoelectric performances.
67

Held & Francke : Cost calculation for building project and the role of cost calculation in achieving competitive advantage

Burnside, Angelica, Lee, Jennifer, Palmquist, Olof January 2007 (has links)
Purpose: The purpose is to gain a better understanding in how a construction com-pany like Held & Francke calculate the price of an offer for a building project and what role cost calculation, in relation to quality and time, plays in achieving competi-tive advantage. Method: Since the method of cost calculation only was investigated at one company we found it suitable for us to use a holistic single case study as the research strategy. The method used in this study is a qualitative research method since our empirical data, to a large extent, is based on interviews. Further, because our study is of a quali-tative nature, we have chosen to perform semi-structured interviews. Conclusions: After examining Held & Francke we found that they manage very well to use some of the theoretical methods for cost calculations. Their main method of calculation is ABC, where the project is broken down into smaller work steps. Cost calculation plays a large role as a competitive advantage for Held & Francke. Cost is the sole as-pect where Held & Francke has full control and providing competitive project prices therefore becomes imperative in order to generate sales. With the focus on costs the cost calculation becomes an important role in achieving a competitive advantage.
68

Theoretical Defect struture and Electronics properties of CuInSe2

Huang, Chi-Lun 28 June 2000 (has links)
Abstract The defect structure of CuMX2 (MºIn, Ga and XºS, Se, Te) was investigated. The defect concentrations were derived as a function of nonmolecularity( X) and nonstoichiometry( Y), and the carrier concentrations were calculated quantitatively using a theoretical defect model, which could be used to select the proper region of stoichiometry for device designs with specified carrier concentrations. The compensation reaction between dopants and intrinsic defects in CuMX2, compound semiconductors is quantitatively illustrated. If for a small increment of temperature the Fermi level EF is shifted by £GEF and the concentration of free majority carriers is increased by £Gn, then the ratio£Gn /£GEFis a measure of the defect-level concentration within£GEF. The electrical and optical properties of CuMX2 have been investigated using various types of electrically active intrinsic defects caused by deviations from the ideal stoichiometry of the compound. The defect complexes are formed by reactions among the impurity and native defects and/or among the native defects during crystal growth or during processing, and play a significant role in determining the characteristics and performance of devices by affecting lifetimes, degradation and breakdown etc.
69

Scattered neutron tomography based on a neutron transport problem

Scipolo, Vittorio 01 November 2005 (has links)
Tomography refers to the cross-sectional imaging of an object from either transmission or reflection data collected by illuminating the object from many different directions. Classical tomography fails to reconstruct the optical properties of thick scattering objects because it does not adequately account for the scattering component of the neutron beam intensity exiting the sample. We proposed a new method of computed tomography which employs an inverse problem analysis of both the transmitted and scattered images generated from a beam passing through an optically thick object. This inverse problem makes use of a computationally efficient, two-dimensional forward problem based on neutron transport theory that effectively calculates the detector readings around the edges of an object. The forward problem solution uses a Step-Characteristic (SC) code with known uncollided source per cell, zero boundary flux condition and Sn discretization for the angular dependence. The calculation of the uncollided sources is performed by using an accurate discretization scheme given properties and position of the incoming beam and beam collimator. The detector predictions are obtained considering both the collided and uncollided components of the incoming radiation. The inverse problem is referred as an optimization problem. The function to be minimized, called an objective function, is calculated as the normalized-squared error between predicted and measured data. The predicted data are calculated by assuming a uniform distribution for the optical properties of the object. The objective function depends directly on the optical properties of the object; therefore, by minimizing it, the correct property distribution can be found. The minimization of this multidimensional function is performed with the Polack Ribiere conjugate-gradient technique that makes use of the gradient of the function with respect to the cross sections of the internal cells of the domain. The forward and inverse models have been successfully tested against numerical results obtained with MCNP (Monte Carlo Neutral Particles) showing excellent agreements. The reconstructions of several objects were successful. In the case of a single intrusion, TNTs (Tomography Neutron Transport using Scattering) was always able to detect the intrusion. In the case of the double body object, TNTs was able to reconstruct partially the optical distribution. The most important defect, in terms of gradient, was correctly located and reconstructed. Difficulties were discovered in the location and reconstruction of the second defect. Nevertheless, the results are exceptional considering they were obtained by lightening the object from only one side. The use of multiple beams around the object will significantly improve the capability of TNTs since it increases the number of constraints for the minimization problem.
70

Held & Francke : Cost calculation for building project and the role of cost calculation in achieving competitive advantage

Burnside, Angelica, Lee, Jennifer, Palmquist, Olof January 2007 (has links)
<p>Purpose: The purpose is to gain a better understanding in how a construction com-pany like Held & Francke calculate the price of an offer for a building project and what role cost calculation, in relation to quality and time, plays in achieving competi-tive advantage.</p><p>Method: Since the method of cost calculation only was investigated at one company we found it suitable for us to use a holistic single case study as the research strategy. The method used in this study is a qualitative research method since our empirical data, to a large extent, is based on interviews. Further, because our study is of a quali-tative nature, we have chosen to perform semi-structured interviews.</p><p>Conclusions:</p><p>After examining Held & Francke we found that they manage very well to use some of the theoretical methods for cost calculations. Their main method of calculation is ABC, where the project is broken down into smaller work steps. Cost calculation plays a large role as a competitive advantage for Held & Francke. Cost is the sole as-pect where Held & Francke has full control and providing competitive project prices therefore becomes imperative in order to generate sales. With the focus on costs the cost calculation becomes an important role in achieving a competitive advantage.</p>

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