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The half-lives of Sr90 and Cs137 were measured by the method of observing the disintegration rate rate of a known number of atoms. A 4(pi) proportional counter was designed and constructed to measure the absolute disintegration rates of the samples used. The efficiency of the counter was tested with calibrated radioactive solutions from the National Bureau of Standards. The submicrogram quantities of the carrier-free radioisotopes used for counting were determined with the mass spectrometer along with isotope dilution techniques. Independent evidence is given to support the half-lives found in this investigation. / Thesis / Master of Science (MS)

Depuis les cinquante dernières années, les préoccupations d’ordre énergétique sont au cœur de l’actualité. Or, une grande partie de l’énergie produite est rejetée et perdue sous forme de chaleur. Ainsi, la récupération d’énergie par des générateurs thermoélectriques apparaît comme une solution pour le mixe énergétique de demain.La thermoélectricité est la conversion directe et réciproque entre énergie thermique et électrique. Les générateurs thermoélectriques sont constitués d’un assemblage de plots de semi-conducteurs de type n et p. Un gradient de température appliqué entre les deux faces du générateur entraîne une migration des charges du matériau qui génère un courant électrique.Les systèmes thermoélectriques ont attiré l’attention du monde scientifique grâce à leurs avantages comparativement aux moyens de récupération d’énergie plus conventionnels. Ce sont des dispositifs compacts, statiques, silencieux et fiables, qui possèdent une longue durée de vie sans nécessiter de maintenance et impactant peu l’environnement.Pour la récupération d'énergie, le challenge actuel est la perte d’énergie thermique des automobiles et des camions ainsi que la chaleur perdue générée dans les industries de la métallurgie ou du nucléaire, par exemple. Ces deux segments nécessitent l’utilisation de modules thermoélectriques ayant un rendement optimum dans la gamme de température 300-600 °C.La performance d’un matériau thermoélectrique est exprimée par le facteur de mérite ZT, donné par l’expression : ZT=S2σT/к. Un ZT élevé peut être obtenu en optimisant les propriétés de transport du matériau. Le coefficient de Seebeck (S), et la conductivité électrique (σ), doivent être le plus élevé possible, alors que la conductivité thermique (κ) doit rester faible.Afin d’être viable pour une production industrielle, un matériau thermoélectrique doit répondre à un certain nombre de critères. Premièrement, ses composants doivent être non toxiques, peu chers et abondants. Ensuite, la voie de fabrication doit être robuste et compatible avec une production en grand volume. Enfin, les matériaux élaborés doivent posséder des propriétés thermoélectriques satisfaisantes dans la gamme de température de l’application visée. Ils doivent également être stables selon les environnements liés à l’application et avoir une bonne tenue mécanique.Les matériaux de type half-Heusler apparaissent comme prometteurs pour la génération de puissance thermoélectrique dans la gamme de température 300-600 °C. En effet, ils possèdent un coefficient de Seebeck et une conductivité électrique élevés. Cependant, leur conductivité thermique est relativement haute comparée aux autres matériaux thermoélectriques.Ce travail de thèse s’est donc focalisé sur l’étude des relations microstructure-propriétés thermoélectriques de matériaux half-Heusler de composition générique (Hf,Zr,Ti)Ni(Sb,Sn) et (Hf,Zr,Ti)Co(Sb,Sn) et de leurs possibles variantes. Les compositions testées ont toutes été synthétisées de la même manière : une fusion par induction permet d’obtenir des lingots qui sont ensuite réduits en poudre par broyage, celle-ci est ensuite frittée par frittage SPS (spark plasma sintering) afin d’obtenir une pastille dense et polycristalline. Les propriétés thermoélectriques et la microstructure de ces échantillons sont ensuite caractérisées et discutées.Un des objectifs de ce travail de thèse était également de réduire coût au kilogramme de ces matériaux half-Heusler, sans impacter de manière négative leurs propriétés thermoélectriques. Nous y sommes parvenus, d’une part, en réduisant la concentration en hafnium incorporé dans les formulations, et d’autre part, en simplifiant le processus de fabrication. En effet, nous avons observé qu’une synthèse sous air des poudres half-Heusler permettait la formation in-situ de précipités d’oxydes, agissant comme source de diffusion des phonons et donc favorisant la diminution de la conductivité thermique. / The search for alternative energy technologies has taken an accelerated pace in the last 50 years due to an increasing concern about climate change. In this quest to find new energy sources, it is interesting to point out that a lot of energy is wasted as heat released into the environment. As a potential solution, thermoelectric power generators could be used to transform the waste heat into useful electrical energy.Thermoelectric generators are converting directly heat into electricity and vice versa. They consist in an assembly of n and p-type semiconducting legs connected electrically in series and thermally in parallel. An applied temperature difference between n and p-sides drives charge carriers displacement in the material from the hot side to the cold one. Therefore a current flow is generated through the circuit. Thermoelectric devices have attracted interest because of their advantages over conventional power generator: no moving part, no liquid involved, reliability, noiseless, long life time without maintenance and also low environmental impact.Over the last several decades, the increased energy demand combined to the environmental concerns, leads to another potential use of thermoelectricity as an alternative energy source by recovering the huge amount of heat lost in industrial or domestic applications. Presently, wasted-heat recovery in cars and trucks and wasted-heat in industry (metallurgy/nuclear…) are becoming a major concern. Both recovery problematics may be addressed using thermoelectric devices efficient in the 300-500 °C temperature range.Numerous thermoelectric materials couples have been investigated and developed over the last 20 years. Most of the already known class of thermoelectric materials have been improved and new classes have been developed, leading to a significant improvement of ZT values being optimum in different temperature ranges. In order to be efficient and to be viable for large scale manufacturing of power generators, a thermoelectric material has to fulfill several requirements. First, the raw materials chosen have to be non-toxic, cheap and abundant. Secondly, the manufacturing process should be robust and compatible to the production of a high volume of materials per day. Last but not least, the elaborated materials have to exhibit acceptable thermoelectric properties in the temperature range of interest for the final application. They must also have a long-term thermal stability in different kinds of environments and good mechanical properties.Half-Heusler materials have been shown to be good candidates in the 300 to 600 °C temperature range. Indeed, due to their semiconductor like band structure, they exhibit a large Seebeck coefficient and high electrical conductivity. Unfortunately, half-Heusler’s thermal conductivity is rather high when compared to other thermoelectric materials. Therefore, the main research efforts on half-Heusler formulations, devoted to be used for thermoelectric applications, have been focused on decreasing the thermal conductivity, while keeping a good electronic transport.Accordingly the main objective of the PhD thesis was to investigate the link between the microstructure and the thermoelectric properties of n and p-type half-Heusler alloys from the generic compositions MNiSn (n-type) and MCoSb (p-type), with M being Ti, Zr and Hf. All investigated compositions have been elaborated by a three step process: (i) ingots synthesis using cold crucible levitation melting, (ii) subsequent ball milling to obtain a calibrated powder and (iii) sintering by spark plasma sintering to obtain dense polycrystalline pellets that are characterized regarding their microstructure and thermoelectric properties from room temperature to 500-600 °C.

The first topic of this thesis is a practical load-optimized VCO design for low-jitter 5V 500 MHz digital phase-locked loop. Besides the low jitter advantage, the design also possesses another feature, i.e., fast locked time. The second topic is the half-swing PLA circuit. An additional 1/2 VDD voltage source and buffering transmission gates are inserted between the NOR planes of PLAs to erase the racing problem and shorten the rise delay as well as the fall delay of the output response such that the speed is enhanced and the dynamic power is reduced. The third topic is a novel design of a the 1.0 GHz pipelining 8-bit CLA based on the architecture we mentioned in the second topic. The operating clock frequency is 1.0 GHz and the output of the addition of two 8-bit binary numbers is done in 2 cycles ( 2.0 ns ).

The present study looked at the internal reliability of the PEAK Relational Training Assessment, using a split-half method of measurement. The reliability of the assessment questions within each of the four factors, within the PEAK Relational Training Assessment was estimated through this process. Eighteen participants, between the ages of 26 months and ten years old were included in the study. All participants had been diagnosed with either a language based or developmental disability, including autism, seizure disorder, Down syndrome and related language disorders. The PEAK Relational Training Assessment (PEAK-D) was administered by a direct-care provider for each of the 18 participants and during standard instructional periods. Results indicate that for each of the 18 participants, there was a strong correlation between scores when one half of the items in each factor were compared to the remaining half. Results did show internal reliability for the PEAK-D when using split-half methodology.

Spintronics or spin-electronics attempt to utilize the electronic spin degree of freedom to make advanced materials and devices for the future. Heusler materials are considered very promising for spintronics applications as many highly spin-polarized materials potentially exist in this family. To accelerate materials discovery and development, The Materials Genome Initiative (https://www.mgi.gov/) was undertaken in 2011 to promote theory-driven search of new materials. In this thesis work, we outline our effort to develop several new materials that are predicted to be 100% spin-polarized (half-metallic) and thermodynamically stable by theory. In particular, two Mn-based Heusler families were investigated: Mn2CoZ (Z= Ga, Sb, Ge) and Mn2FeZ (Z=Si,Ge), where the latter is potentially a new Heusler family. These materials were synthesized using the arc-melting technique and their crystal structure was investigated using the X-ray diffraction (XRD) method before and after appropriate annealing of the samples. Preliminary magnetometry measurements are also reported. We first developed a heat-treatment procedure that could be applied to all the Mn-based compounds mentioned above. Mn2CoGa was successfully stabilized in the cubic inverse-Heusler phase with a=5.869 Å and magnetic moment of 2.007 /fu. This is in good agreement with prior literature reports [1]. However, cubic phases of Mn2CoSb and Mn2CoGe could not be stabilized within the annealing temperature range that is accessible in our lab. We successfully synthesized a cubic Mn2FeSi phase using an annealing procedure similar to Mn2CoGa. The measured cubic lattice parameter of Mn2FeSi was 5.682 Å. This is the first experimental report of this material to the best of our knowledge. Detailed analysis of relative intensities of different X-ray peaks revealed that the structure is most likely in an inverse Heusler phase, in agreement with theory. However, a substantial atomic-level disorder was also uncovered from XRD analysis that requires further investigation to understand its effect on its magnetism and half-metallicity. Mn2FeGe showed the existence of non-cubic phases that substantially weakened at high annealing temperatures.

Loops automórficos, ou A-loops, são loops nos quais todas as aplicações internas são automorfismos. Esta variedade de loops inclui grupos e loops de Moufang comutativos. Loops automórficos diedrais formam uma classe de A-loops construda a partir da duplicação de grupos abelianos finitos, generalizando a construção do grupo diedral. Outra classe de A-loops é a dos loops automórficos de Lie, construda a partir de anéis de Lie, definindo-se uma nova operação entre seus elementos. Um half-isomorfismo é uma bijeção f entre loops L e L\' onde, para quaisquer x e y pertencentes a L, temos que f(xy) pertence ao conjunto . Dizemos que o half-isomorfismo f é não trivial quando f não é um isomorfismo e nem um anti-isomorfismo. Nesta tese descrevemos propriedades de half-isomorfismos de loops, classificamos os half-isomorfismos entre loops automórficos diedrais e obtivemos o grupo de half-automorfismos nesta classe. Para os loops automórficos de Lie de ordem mpar, mostramos que todo half-automorfismo é trivial. / Automorphic loops, or A-loops, are loops in which every inner mapping is an automorphism. This variety of loops includes groups and commutative Moufang loops. Dihedral automorphic loops form a class of A-loops, constructed from the duplication of finite abelian groups, that generalizes the construction of the dihedral group. Another class of A-loops is the Lie automorphic loops, constructed from Lie rings, where a new operation between its elements is defined. A half-isomorphism is a bijection f between loops L and L\' where, for any x and y belong to L, we have that f(xy) belongs to the set {f(x)f(y),f(y)f(x)}. We say that half-isomorphism f is non trivial when f is neither an isomorphism nor an anti-isomorphism. In this thesis, we describe properties of half-isomorphisms of loops, we classify the half-isomorphisms between dihedral automorphic loops and we obtain the group of half-automorphisms in this class. For the Lie automorphic loops of odd order, we show that every half-automorphism is trivial.

Loops automórficos, ou A-loops, são loops nos quais todas as aplicações internas são automorfismos. Esta variedade de loops inclui grupos e loops de Moufang comutativos. Loops automórficos diedrais formam uma classe de A-loops construda a partir da duplicação de grupos abelianos finitos, generalizando a construção do grupo diedral. Outra classe de A-loops é a dos loops automórficos de Lie, construda a partir de anéis de Lie, definindo-se uma nova operação entre seus elementos. Um half-isomorfismo é uma bijeção f entre loops L e L\' onde, para quaisquer x e y pertencentes a L, temos que f(xy) pertence ao conjunto . Dizemos que o half-isomorfismo f é não trivial quando f não é um isomorfismo e nem um anti-isomorfismo. Nesta tese descrevemos propriedades de half-isomorfismos de loops, classificamos os half-isomorfismos entre loops automórficos diedrais e obtivemos o grupo de half-automorfismos nesta classe. Para os loops automórficos de Lie de ordem mpar, mostramos que todo half-automorfismo é trivial. / Automorphic loops, or A-loops, are loops in which every inner mapping is an automorphism. This variety of loops includes groups and commutative Moufang loops. Dihedral automorphic loops form a class of A-loops, constructed from the duplication of finite abelian groups, that generalizes the construction of the dihedral group. Another class of A-loops is the Lie automorphic loops, constructed from Lie rings, where a new operation between its elements is defined. A half-isomorphism is a bijection f between loops L and L\' where, for any x and y belong to L, we have that f(xy) belongs to the set {f(x)f(y),f(y)f(x)}. We say that half-isomorphism f is non trivial when f is neither an isomorphism nor an anti-isomorphism. In this thesis, we describe properties of half-isomorphisms of loops, we classify the half-isomorphisms between dihedral automorphic loops and we obtain the group of half-automorphisms in this class. For the Lie automorphic loops of odd order, we show that every half-automorphism is trivial.

Previous work in the Rosenberg group showed that the half-sandwich complexes Ru(η5-indenyl)Cl(PR2H)(PPh3) (2i), where R = cyclohexyl (Cy), isopropyl (Pri), phenyl (Ph), para-tolyl (Tolp), react with the strong, bulky base KOBut to give highly reactive complexes Ru(η5-indenyl)(PR2)(PPh3) (6i) containing a ruthenium-phosphorus double bond, Ru=PR2. The reactions of these phosphido complexes 6i with some reagents, such as alkenes, carbon monoxide and dihydrogen, illustrate their rich and varied reactivity. To better understand the mechanisms of these reactions (whether the indenyl effect is necessary), synthesis of analogous secondary phosphine complexes containing the pentamethylcyclopentadienyl (Cp*) ligand, Ru(η5-Cp*)Cl(PPh3)(PR2H) (2) were prepared via ligand substitution at Ru(η5-Cp*)Cl(PPh3)2 (1). Cp* phosphido complexes Ru(η5-Cp*)(PR2)(PPh3) (6) were generated in situ and their reactivity was investigated to see if they behaved similarly to the indenyl complexes. Experimental evidence in this thesis suggests that variable hapticity is not necessary in our indenyl system. In addition, these experimental evidence highlights enhanced lability of ligand at the bulky Cp*Ru fragment and higher Bronsted basicity of the phosphido ligand (PR2-) in Cp* phosphido 6 relative to the indenyl analogues 6i. / Graduate / 2017-12-11 / 0488 / yangjin@uvic.ca

The present investigation was prompted by several considerations. In previous studies there was considerable variance with regard to the reported values for the half-lives of the isomeric and ground states in 164 Ho. There was also considerable variance with regard to the values reported for the branching ratios and the relative intensities of the transitions. Thus a further study of the problem was needed.