El control dels nivells d'oxigen és una etapa crítica en molts processos industrials.
En alguns d'aquests, els nivells d'oxigen han de ser detectats i controlats fins i tot en el rang de les ppm. Encara que ja es coneguin molts mètodes, ja provats per a la detecció d'oxigen, la majoria d'ells són costosos i complexes. Altres mètodes més accessibles com els sensors Lambda i les cel·les electroquímiques també presenten alguns problemes. Els primers requereixen d'elevades concentracions d'oxigen o bé de controls de temperatura força precisos amb la finalitat de treballar sense interferència d'altres gasos. Els segons es poden veure afectats per temps d'exposició massa perllongats a gasos "àcids" com el diòxid de carboni i no es recomana el seu ús en atmosferes amb un contingut de més del 25% d'aquests gas.
Són moltes les avantatges dels sensors de gasos: baix cost, mida reduïda i solidesa entre d'altres. Això fa que aquests dispositius despuntin com a solució per a la detecció d'oxigen. Molts autors han fet esment a la detecció d'oxigen a nivells de ppm emprant aquests tipus de sensors. De totes formes, la majoria s'han desenvolupat mitjançant tecnologia de capa fina. En aplicacions industrials, la tecnologia més usada és la de capa gruixuda, ja que aquests sensors són més fàcils de fabricar i de dopar que els de capa fina. En el cas dels sensors de capa gruixuda la detecció de traces d'oxigen és una tasca encara difícil i es necessita treballar a elevades temperatures (> 700 ºC).
El mecanisme de detecció d'oxigen en els sensors basats en òxids semiconductors es basa en la interdependència de la conductivitat elèctrica d'aquests òxids i la pressió parcial d'oxigen en l'ambient. El diòxid de titani és l'òxid semiconductor que més s'usa en la detecció d'oxigen. Els sensors basats en òxid de titani (en fase cristal·lina rutil) necessiten d'elevades temperatures per a un correcte funcionament (700 ºC-1000 ºC), ja que la detecció d'oxigen en la fase rutil es deu principalment a la difusió dels ion d'aquests gas en el volum del material. Per a que es produeixi la reacció en el volum o propi cos del material es necessiten elevades temperatures. Això comporta un consum també elevat de potència, que a la llarga serà un problema en determinades aplicacions industrials.
Al tenir l'òxid de titani en fase anatasa més electrons lliures, la reacció de l'oxigen amb aquests material es pot associar a una reacció superficial. Aquesta reacció es pot donar a temperatures més baixes, al voltant dels 400 ºC-500 ºC i per tant, mantenir la fase anatasa en l'òxid permet disminuir la temperatura de treball, la qual cosa és desitjable per al disseny del sensor.
Tal i com es reflecteix en algunes referències bibliogràfiques, en dopar l'òxid de titani amb ions pentavalents com el Nb5+, aquests ions s'introdueixen en l'estructura cristallina de l'òxid de titani en fase anatasa, creant certa tensió interna que provoca una resistència al canvi de fase anatasa a rutil, inhibint el creixement del gra.
Per altra banda, també s'ha posat de manifest en moltes fonts que el dopatge d'òxid de titani amb niobi augmenta la sensibilitat d'aquests material vers l'oxigen. Aquests dopatge fa que l'òxid presenti una impedància menor, per la qual cosa es facilita el disseny de l'electrònica associada al sensor.
Tenint en compte aquestes dues premisses, un dels objectius d'aquesta tesi ha estat la síntesi, mitjançant la tècnica del sol-gel, de diferents tipus d'òxid de titani per a la fabricació d'un sensor d'oxigen que operi en una marge de temperatura relativament moderat (300 ºC-600 ºC). Es treballà amb òxids sense dopar i amb òxids dopats amb un 3 % de niobi.
Cadascun es calcinà a diferents temperatures: 600 ºC, 700 ºC, 800 ºC i 900 ºC.
Amb l'objectiu de correlacionar l'estructura i la sensibilitat i selectivitat dels òxids sintetitzats, aquests es van sotmetre a diferents tècniques de caracterització. En primer lloc l'espectrometria de plasma acoblada inductivament (ICP) s'utilitzà amb el fi de determinarne la composició química i quantificar la proporció de cada component. En segon lloc també es va fer servir la difracció de raigs X (XRD) per a determinar les fases cristallines de l'òxid i la mida dels cristalls. També es va analitzar la porositat i es van fer mesures de l'àrea superficial (BET) dels nanopols . En darrer lloc, la microscopia d'escàner d'electrons (SEM) fou aplicada amb la finalitat d'obtenir detalls de l'estructura de la capa activa i de la grandària dels grans. Per a l'anàlisi quantitatiu i també qualitatiu de les capes s'utilitzà l'espectroscopia de dispersió d'energia per raig X (EDS).
Com a substrat, es va desenvolupar un substrat d'alúmina que pot albergar quatre capes actives treballant a una mateixa temperatura, conformant així una matriu de sensors.
Treballant amb aquests substrat aparegueren certs inconvenients (relacionats amb l'encapsulat del sensor) operant a temperatures superiors als 450 ºC. Això comportà un retard en l'obtenció de resultats amb aquests substrat i es decidí introduir-ne un de nou, resistent a altes temperatures i adquirit en l'Institut Kurchatov (Moscou, Rússia). Tots els resultats presentats en aquesta tesi es van obtenir amb l'ús d'aquests últim substrat. En l'actualitat s'està treballant amb el primer d'ells.
Un cop fabricat els sensors, es provà la sensibilitat d'aquests en un sistema de flux continu. Es provaren tres diferents concentracions: 20 ppm d'O2 amb balanç de N2, 30 ppm d' O2 amb balanç CO2 i 15 ppm d'O2 amb balanç CO2. També es testaren les respostes dels sensors cap a altres gasos interferents (SO2, CH4, H2S i C2H4) per a determinar la selectivitat d'aquests sensor vers l'O2 en presència d'interferents.
La millor resposta vers l'oxigen s'aconseguí amb els sensors dopats i calcinats a 700 ºC. Aquesta millora es pot atribuir al dopatge amb niobi. Aquets metall inhibeix el creixement del gra i per tant s'aconsegueixen òxids amb major àrea superficial. Un altre motiu pot ser el retard del pas de la fase rutil a la fase anatasa induït també pel dopatge de Niobi.
La sensibilitat denotada pels òxids dopats amb niobi i calcinats a 600 ºC fou molt baixa tot i que en principi aquests òxids presentaven característiques físiques potencialment millors que els calcinats a 700 ºC. Aquests fet es pot explicar degut a la presència d' alguns depòsits de carboni que no es pogueren eliminar durant la calcinació. La presència d'aquests dipòsits fou confirmada per l'anàlisi Raman d'aquests materials. Les estructures de carboni presents en aquests residus cobreixen gran part de la superfície de l'òxid i contribueixen a la desactivació del procés catalític que té lloc en aquesta superfície.
Concernint a les mesures realitzades sota atmosfera de CO2, els òxids dopats amb niobi i calcinats a 700 ºC també respongueren a l'oxigen. La resposta en el cas de 15 ppm d'O2 s'invertí del tipus oxidant a tipus reductor. A baixes concentracions d'oxigen els ion CO- provinents de la dissociació del CO2 s'adsorbeixen a la superfície del material actiu.
L'oxígen, enlloc de deplexionar-se, interactua amb aquests ions per a formar CO2, alliberant electrons a la capa activa i això fa que la natura de la resposta sigui reductora. Les respostes vers altres gasos contaminants com SO2, CH4, H2S foren tipus reductor com era esperat, la qual cosa indicava que el canvi de resposta no era atribuïble al canvi de l'òxid conductor de tipus n a tipus p, si no més aviat en un canvi en la naturalesa de la reacció.
Amb l'objectiu de millorar la sensibilitat de l'òxid dopat es provà d'incrementar la seva àrea superficial i porositat utilitzant un surfactant com a motlle durant el procés de síntesi. El surfactant usat fou la dodecilamina, que forma una estructura miscel·lar que fa de motlle en el procés de nucleació de l'òxid, generant així grans menors amb major àrea superficial i major porositat. De tres diferents temptatives, els millors resultats es varen obtenir quan s'addicionaven 8 ml de dodecilamina a la solució del sol-gel immediatament desprès de la hidròlisi dels alcòxids. Les proves XRD mostraren que l'addició del surfactant retarda encara més la transició de les fases rutil a anatasa i també inhibeix el creixement dels cristalls. Aquests resultats es recolzen sobre les micrografies del SEM i l'anàlisi BET, que revelaren un creixement en la porositat del material i un gra menor. Malgrat aquests resultats prometedors en la determinació estructural, les mesures de l'oxigen amb aquests sensors revelaren una poca sensibilitat dels sensors modificats amb el surfactant. Els espectres RAMAN mostraren alguns pics corresponents a diferents morfologies de carboni.
Els dipòsits d'aquests material en la superfície, tal i que com s'ha mencionat anteriorment, inhibeixen la resposta de la capa activa vers l'oxigen.
El control de los niveles de oxígeno es una etapa crítica en muchos procesos industriales. En algunos de estos procesos, los niveles de oxígeno deben ser detectados y controlados incluso en el rango de las ppm. Aunque existen varios métodos ya probados para la detección de oxígeno en estos sistemas de control, la mayoría de ellos son costosos y complejos. Otros métodos de detección más accesible como los sensores Lambda o las celdas electoquímicas también presentan problemas: los primeros requieren de altas concentraciones de oxígeno, o de controles de temperatura bastante precisos para poder trabajar sin interferencias de otros gases Los segundos pueden verse afectados por una prolongada exposición a gases "ácidos" como el dióxido de carbono y no se recomienda para uso continuo en atmósferas con un contenido de mas del 25 % de dicho gas.
Debido a muchas ventajas tales como su bajo costo, tamaño reducido y solidez, los sensores basados en semiconductores aparecen como una solución para la detección de oxígeno. Algunos autores han reportado la detección de oxígeno a niveles ppm empleando este tipo de sensores. Sin embargo, la mayoría de ellos han sido desarrollados mediante tecnología de capa fina. En aplicaciones industriales, la tecnología más usada es la de capa gruesa, ya que estos sensores son más fáciles de fabricar y de dopar que los sensores de capa fina. En los sensores de capa gruesa, la detección de trazas de oxígeno es aun una tarea difícil de alcanzar, siendo normalmente necesarias altas temperaturas (> 700 ºC) para lograrlo.
El mecanismo de detección de oxígeno en los sensores basados en óxidos semiconductores esta basado en la fuerte dependencia de la conductividad eléctrica de estos materiales a la presión parcial de oxígeno en el ambiente. El dióxido de titanio es el óxido semiconductor más ampliamente usado en la detección de oxígeno. Los sensores basados en TiO2 (usualmente en la fase cristalina rutilo) necesitan trabajar a elevadas temperaturas (700 ºC - 1000 ºC), ya que la detección de oxígeno en la fase rutile se debe principalmente a la difusión de los iones de oxígeno en el volumen del material. Para que se produzca la reacción en el volumen hacen falta altas temperaturas, lo que conlleva un alto consumo de potencia que puede ser un handicap en determinadas aplicaciones industriales.
Por otro lado, el dióxido de titanio en fase anatase posee más electrones libres, así que la detección de oxígeno en este material puede asociarse a una reacción de superficie, la cual tiene lugar a no tan altas temperaturas (400 ºC - 500 ºC).Por lo tanto, puede concluirse que mantener la fase anatase permitiría la detección de oxígeno a temperaturas moderadas, lo cual es deseable para el diseño del sensor.
Se ha reportado que cuando el TiO2 es dopado con iones pentavalentes, i.e. Nb5+, tales iones se introducen en la estructura cristalina de dicho óxido en estado anatase, obstruyendo la transformación de dicha fase a rutile, inhibiendo el crecimiento del grano.
También se ha reportado que el dopado con niobio aumenta la sensibilidad del dióxido de titanio hacia el oxígeno. El óxido dopado también presenta una impedancia más baja a temperaturas de trabajo menores, por lo que se facilita el diseño de la electrónica asociada al sensor.
Basándonos en estos puntos, uno de los objetivos de esta tesis fue la síntesis, mediante un proceso de sol-gel, de diferentes tipos de dióxido de titanio para la fabricación de un sensor de oxígeno que opere en un margen de temperaturas moderado (300 ºC - 600 ºC). Para ello se desarrollaron óxidos dopados con un 3 % de niobio y óxidos sin dopar.
Cada uno de ellos fue calcinado a diferentes temperaturas: 600 ºC, 700 ºC, 800 ºC y 900 ºC.
Con el objetivo de correlacionar la estructura y la sensibilidad y selectividad de los óxidos sintetizados, estos se sometieron a diferentes técnicas de caracterización. La espectroscopia de Plasma Acoplado Inductivamente (ICP) fue empleada para determinar la composición química de las muestras y cuantificar la porción de cada componente. La Difracción de Rayos-X (XRD) fue usada para establecer las fases presentes en la estructura cristalina del material y para determinar el tamaño el tamaño de los cristales en cada material. Se realizaron medidas de área BET con los nanopolvos para conocer el área superficial y la porosidad de cada material. La Microscopia de Escáner de Electrones (SEM) fue aplicado para obtener detalles de la estructura de la capa y del tamaño de las partículas.
Para hacer un análisis cuantitativo y cualitativo de las capas se utilizó la Espectroscopia de Dispersión de Energía por Rayos -X (EDS).
Para realizar las medidas, se desarrolló un substrato de alúmina para ser usado en el sensor de oxígeno. Este substrato puede soportar cuatro capas activas trabajando a la misma temperatura formando una matriz de sensores. Sin embargo, debido a algunos problemas relacionados con el encapsulado del substrato cuando las temperaturas de trabajo sobrepasaban los 450 ºC, su empleo para el sensor de oxígeno se retrasó y los resultados obtenidos con el mismo no estaban lo suficientemente completos para ser presentados en este trabajo. Para solventar la necesidad de un substrato que pudiese resistir altas temperaturas para aplicaciones de detección de oxígeno, se introdujo un nuevo substrato adquirido en el Instituto Kurchatov (Moscú - Rusia). Los resultados expuestos en este trabajo se obtuvieron con este último substrato.
Una vez fabricados los sensores, las capacidades de sensado de los materiales fueron probadas. La sensibilidad hacia el oxígeno fue medida en tres situaciones diferentes: 20 ppm de O2 en balance de N2, 30 ppm y 15 ppm de O2 en balance de CO2. Las respuestas de los sensores hacia otros gases contaminantes (SO2, CH4, H2S y C2H4) también fueron probadas para observar la influencia de dichos gases en el proceso de detección de oxígeno.
La mejor respuesta hacia el oxígeno se consiguió con los sensores basados en materiales dopados calcinados a 700 ºC. Esto puede atribuirse a los iones de niobio que inhiben el crecimiento del grano y por lo tanto producen un aumento del área superficial de dichos materiales, que beneficia al mecanismo de detección, y a su fase cristalina, mayoritariamente anatase, la cual permite la detección a las temperaturas deseadas (300 ºC - 600 ºC). Las especies de niobio también contribuyen al proceso de catálisis.
Otro motivo puede ser la fase cristalina, mayoritariamente anatase, la cual permite la detección a las temperaturas deseadas (300 ºC - 600 ºC).
Por otro lado, los materiales dopados calcinados a 600 ºC tuvieron una pobre respuesta, a pesar de que estos tienen mejores características físicas que los calcinados a 700 ºC. Este hecho puede explicarse por la presencia de algunos depósitos de carbono, residuales del proceso de síntesis, que no pudieron ser eliminados durante la calcinación. La presencia de estos depósitos fue confirmada mediante los análisis Raman de estos materiales.
Ya que estas estructuras de carbono cubren gran parte de la superficie del material, y que además son poco catalíticas, el resultado es una desactivación de la catálisis.
Concerniente a las medidas realizadas en atmósfera de CO2, los óxidos dopados con niobio y calcinados a 700 ºC también respondieron al oxígeno. Sin embargo, la respuesta hacia 15 ppm de oxígeno presentó una inversión de tipo oxidante a tipo reductora. A bajas concentraciones de oxígeno, los iones de CO-, provenientes de la disociación del CO2, se adsorben en la superficie del material activo. El oxígeno, en lugar de deplexionarse, interactúa con estos iones para formar CO2, liberando electrones a la capa activa, dando lugar así a una respuesta reductora. Por otra parte, las respuestas hacia otros gases contaminantes tales como H2S, SO2 y CH4 fueron de tipo reductora, como era esperado, lo cual indica que el cambio de respuesta no puede atribuirse al cambio del óxido conductor de tipo n a tipo p, sino más bien a un cambio en la naturaleza de la reacción.
Para mejorar la sensibilidad de los óxidos dopados, se intentó incrementar su área superficial y porosidad usando un surfactante como plantilla o molde durante el proceso de síntesis. El surfactante empleado fue dodecylamina, la cual forma una estructura micelar que hace de molde durante el proceso de nucleación del óxido, generando así granos menores con mayor área superficial y mayor porosidad. Entre tres diferentes intentos, los mejores resultados se obtuvieron cuando 8ml de dodecylamina fueron agregados a la solución del sol-gel inmediatamente después de la hidrólisis de los alkóxidos. Los análisis de XRD de este material mostraron que la adición de surfactante retarda aun más la transición de fase de anatase a rutile y también evita el crecimiento de los cristalitos. Estos resultados son soportados por las microfotografías de SEM y los análisis BET, los cuales mostraron un retardo en el crecimiento del grano y un incremento del área superficial. El área BET también evidenció un incremento de la porosidad del óxido. Sin embargo, los resultados de las medidas de oxígeno revelaron una pobre respuesta de los sensores basados en el óxido en cuestión. Los espectros Raman de este material mostraron algunos picos correspondientes a carbono con diferentes morfologías. Como fue explicado previamente, estos depósitos de carbono retardan la respuesta de este óxido al oxígeno.
Control of oxygen levels is a critical step in many industrial processes. In some of these processes, levels of oxygen must be detected and controlled even in ppm range.
Although there are several probed methods for oxygen detection in these control systems, most of them are expensive and complex. More accessible methods as Lambda sensors or electrochemical cells present also problems: first ones need high concentration of oxygen, or an extremely accurate temperature control, to work without interference from other gases.
Second ones may be affected by prolonged exposure to "acid" gases such as carbon dioxide and it is not recommended for continuous use in atmospheres which contain more than 25% of CO2.
Due to many advantages as low cost, small size and robustness, semiconductor sensors appear as a good solution for oxygen detection. Some authors had reported detection of oxygen at ppm levels employing this kind of sensors. However, most of them were made through thin film technology. For industrial applications, the most usual technology is thick film, because it is easier to fabricate and to dope than thin film sensors. For thick film sensors, detection of traces of oxygen is still a very difficult goal to reach and usually high temperatures (>700 ºC) are needed.
The basic oxygen sensitivity mechanism of oxygen sensors based on semiconductor oxides is their strong dependencies of electrical conductivity on oxygen partial pressures.
Titanium dioxide is the semiconductor material most widely used for oxygen detection.
Titania (usually rutile crystalline phase) based sensors need to work at high temperatures (700 ºC - 1000 ºC), since oxygen detection in rutile state is mainly due to diffusion of oxygen ions in the bulk of the material. For bulk reaction it is necessary to work at these high temperatures, leading to high power consumption, which is not desirable for electronic applications.
On the other hand, anatase state Titania has more free electrons. So, oxygen detection can be associated to surface reactions, which take place at not so high temperatures (400 ºC - 500 ºC). Then, it can be derived that maintaining an anatase structure would allow the detection of oxygen at medium temperatures, which is desirable for sensor design.
It had been reported that when Titania is doped with pentavalent impurity ions, i.e. Nb5+, such ions get into the anatase Titania crystalline structure, giving rise to a hindering in the phase transformation to rutile and an inhibition in grain growth. It has been also reported that Nb-doped Titania shows higher sensitivity towards oxygen than pure TiO2. The doped material also shows lower impedance at low operating temperatures and hence, it is easier to design associated electronic circuitry.
In this work pure Titania and Niobium doped Titania nanopowders were synthesized by a simplified sol-gel route. Based on the literature, the doping concentration in doped materials was set to Nb/Ti = 3 at%. In order to set the crystalline structure of the active materials, they were calcined at four different temperatures: 600 ºC, 700 ºC, 800 ºC and 900 ºC.
The obtained materials were characterized by different techniques. The objective of these characterizations was to obtain information about the material structure that could be related to its detection properties. Inductively Coupled Plasma (ICP) spectroscopy was employed to determine the chemical composition of the samples and quantify the amount of each component. X-ray Diffraction (XRD) was used to establish the phases present in the crystalline structure of the material and to determine the size of the crystallites in each material. Area BET measurements were done to nanopowders to know the surface area and the porosity of each material. Scanning Electron Microscopy (SEM) was used to obtain details on the film structure and the grain size. To make quantitative and qualitative analysis, Energy-Dispersive X-ray Spectroscopy (EDS) was also applied.
For the measurements, an alumina substrate was developed to be used in the oxygen sensor. This substrate can support four active layers working at the same temperature forming a sensor array. However, due some problems related with the substrate package at working temperatures above 450 ºC, the use of this substrate for oxygen sensor application was delayed and the results obtained whit it were not complete enough to be presented in this work. In order to resolve the necessity of a substrate that can resist high working temperatures for oxygen sensing applications, it was introduced a new substrate acquired from the Kurchatov Institute (Moscow-Russia). The results exposed in this work were obtained by using this last substrate.
Using these substrates, the sensing capabilities of the materials were also tested. The sensitivity toward oxygen was measured under three different conditions: 20 ppm of O2 in N2 balance, 30 ppm and 15 pmm of O2 in CO2 balance. The sensors responses toward other pollutant gases (SO2, CH4, H2S and C2H4) were also tested in order to see the influence of such gases in the oxygen detection process.
The best response toward oxygen was achieved in those sensors based on Nb-doped materials calcined at 700 ºC. This may be attributed to the niobium ions which hinder the grain growth and hence give rise to a high surface area that benefits the detection mechanism. The good response may be also attributed to the crystalline phase, mostly anatase, which allows the detection at desire temperatures (300 ºC - 600 ºC).
On the other hand, the doped materials calcined at 600 ºC had a poor response, in spite of they have better physical characteristics than doped materials calcined at 700 ºC.
This problem was mainly related to some carbon deposits detected in these materials trough Raman analyses. Such carbon deposits may be residual of the synthesis process, which could not be eliminated during the calcination. Since these carbon structures cover a great part of the material surface, and they are also poorly catalytic, the result is a deactivation of the catalysis.
Concerning to the measurements carried out under CO2 atmosphere, Nb-doped Titania calcined at 700 ºC also responded to oxygen. However, the response toward 15 ppm of oxygen presented an inversion from oxidative type to reductive type. At low oxygen concentrations, the CO- ions from CO2 disassociation are adsorbed on the active material surface. The oxygen, instead deplexing, interacts with these ions forming CO2, liberating electrons to the active layer giving rise to a reductive type response. On the other hand, the responses toward other pollutant gases such H2S, SO2, C2H4 and CH4 were of reduction type, as they were expected, which support the idea that the change in the response type is not due to the change in the physics of the semiconductor oxide from n type to p type, but to a change in the reaction nature.
In order to improve the sensing capabilities of doped materials, it was attempted to increase their surface area and porosity by using a surfactant as a template during the synthesis process. The surfactant employed was dodecylamine, which forms a micellar structure that works as template in the nucleation process of the oxide, generating small grains with higher surface area and porosity. Among three different attempts, the best results were obtained when 8 ml of surfactant were added to the sol-gel solution just after the hydrolysis of the metal alkoxides. XRD analyses of this material showed that the addition of surfactant retards even more the phase transition from anatase to rutile and also hinder the crystallites growth. These results were supported by SEM micrographs and BET analysis, which show a hinder in grain growth and an increase of the surface area. Area BET also evidences an increment of the material porosity. However, the results of the oxygen measurement reveal a poor response of the considered material. The Raman spectroscopy of this oxide shows some peaks that correspond to carbon with different morphologies. As it was explained before, these deposits of carbon retard the response of this material toward oxygen.

In this work, an electrochemical method based on a cyt c biosensor has been developed, for the detection of selected arsenic and cyanide compounds. Boron Doped Diamond (BDD) electrode was used as a transducer, onto which cyt c was immobilised and used for direct determination of Prussian blue, potassium cyanide and arsenic trioxide by inhibition mechanism. The sensitivity as calculated from cyclic voltammetry (CV) and square wave voltammetry (SWV), for each analyte in phosphate buffer (pH= 7) was found to be (1.087- 4.488 ×10-9 M) and the detection limits ranging from 0.0043- 9.1 μM. These values represent a big improvement over the current Environmental Protection Agency (EPA) and World Health Organisation (WHO) guidelines.

La automatización de métodos de preparación de muestra es un tema de gran actualidad para reducir tiempos de análisis y mejorar las propiedades analíticas de ensayos químicos. Como consecuencia, en esta tesis doctoral se proponen nuevos métodos de preparación de muestra automáticos y acoplados a técnicas analíticas usando las diferentes generaciones de análisis en flujo para la determinación de contaminantes inorgánicos y orgánicos en muestras de interés ambiental y en residuos industriales. La tesis doctoral se compone de dos partes: La primera se centra en el desarrollo de nuevos métodos automáticos de fraccionamiento químico dinámico e investigación de la bioaccesibilidad de trazas de contaminantes inorgánicos en muestras sólidas, como por ejemplo, cenizas volantes y biomasa vegetal. La segunda parte incluye nuevos métodos automáticos de (ad/ab)sorción previos a ensayos cromatográficos para la extracción, preconcentración, separación y determinación de niveles traza de varias familias de pesticidas (ej., triazinas y sus metabolitos, y compuestos bifenilos policlorados (PCBs)) en muestras ambientales a concentraciones inferiores a las legisladas. A diferencia de los métodos de fraccionamiento basados en equilibrio, los métodos dinámicos en flujo son capaces de cuantificar con mayor exactitud la fracción de metales potencialmente bioaccesible al cambiar las condiciones ambientales como consecuencia del desplazamiento de los equilibrios sólido/líquido y la inexistencia de efectos de readsorción de metales. De hecho, los procesos naturales ocurren en condiciones dinámicas en vez de estáticas, que son asumidas en los métodos clásicos. En este contexto, se diseñó un sistema en flujo miniaturizado basado en la extracción en un reactor agitado para la cuantificación de forma automática de la fracción bioaccesible de elementos traza (Cu, Cd, Ni, Pb y Zn) en tres muestras simultáneamente y con cantidades de muestra variable hasta 1.0 g. Se utilizó un método de extracción secuencial de dos etapas basado en el uso de agua y ácido acético (o tampón ácido acético/acetato) como extractantes para la determinación de las máximas fracciones móviles de elementos traza en cenizas volantes mediante el procedimiento americano de lixiviación característica de toxicidad (US-TCLP). Los resultados experimentales se detallan en el capítulo 3 titulado “Fraccionamiento automático y simultáneo de elementos traza en cenizas volantes usando un sistema múltiple de reactores agitados”. En las extracciones dinámicas la muestra a analizar se coloca en un recipiente adecuado y se expone continuamente a nuevos volúmenes de extractante mediantes sistemas en flujo. En esta tesis, se comparan dos sistemas de extracciones dinámicas basados en el uso de microcolumnas o reactores agitados en sistemas en flujo (Inyección secuencial, SIA) en cuanto al tipo de recipiente para la muestra, representatividad y homogeneidad de la muestra y resultados analíticos, con el objetivo final de armonizar esta nueva metodología de lixiviación. Para ello se evaluó la extractabilidad de Cu, Ni, Pb and Zn en un material de referencia certificado de cenizas de carbón (NIST 1633b) utilizando el método BCR de tres etapas recomendado por la UE. Este trabajo se incluye en el capítulo 4 títulado: “Evaluación crítica de nuevos métodos dinámicos en flujo para la extracción automática de metales traza en cenizas usando el método BCR de extracción secuencial”. Para investigar la posible disponibilidad de elementos responsables de la generación de cenizas (ej., K, Ca, Na y Mg) en biomasa (corteza y ramas de árboles) en gases de combustión se diseñó un sistema en-línea acoplando extracción dinámica basada en reactores agitados a un espectrómetro de plasma acoplado inductivamente con detección óptica. Las fracciones móviles de metales alcalinos y alcalino-térreos son indicadoras de posibles problemas en los sistemas de combustión (formación de depósitos y pérdida de eficacia del reactor) dónde se utilice la biomasa como combustible. Los resultados experimentales se describen en el capítulo 5 titulado: “Método de fraccionamiento químico dinámico con detección elemental por espectrometría de plasma para la caracterización avanzada de biocombustibles sólidos”. El objetivo final de este trabajo es disponer de un método analítico fiable para decidir a la mayor brevedad posible si diferentes tipos de biomasa podrían ser utilizados como combustibles en base a los riesgos de corrosión en reactores. Para elucidar asociaciones entre ceniza/biomasa y metales e investigar la selectividad real de los extractantes, se combinaron los resultados de extracción dinámica con técnicas de caracterización espectroscópica, como por ejemplo, la microscopía electrónica de barrido con espectrometría de fluorescencia de rayos X dispersiva (SEM-EDX) y difracción de rayos X (RXD). Estos estudios se incluyen en el capítulo 6 titulado: “Elucidación de asociaciones de elementos responsables de la generación de cenizas en residuos de biomasa”. En la segunda parte de la tesis se incluyen nuevos métodos automáticos de preparación de muestra basados en la extracción en fase sólida (SPE) en sistemas en flujo acoplados a técnicas cromatográficas (GC o LC) para la determinación de contaminantes orgánicos. En el capítulo 7 titulado: “Microextracción en fase sólida basada en bead-injection multimodal usando polímeros de impresión molecular y materiales de fase reversa para análisis automático de multi-residuos de herbicidas/pesticidas” se propone un método μSPE selectivo con fase sólida renovable de forma automática, denominado Bead-Injection-SPE multidimensional, combinando polímeros de impresión molecular (MIP) y materiales de fase reversa (Oasis HLB) para la preconcentración selectiva de residuos de triazinas y sus metabolitos en extractos crudos de suelos. Se demostró que el acoplamiento μSPE-LC proporciona suficiente sensibilidad y fiabilidad para la determinación de los analitos a niveles de concentración inferiores a los legislados en aguas de consumo humano y aguas superficiales. En el capítulo 8 titulado: “Método de extracción en fase sólida miniaturizado basado en la dispersión de nanofibras de carbono en sistemas en flujo para la determinación automática de niveles traza de contaminantes orgánicos prioritarios mediante LC” se utilizaron nanomateriales de carbono como adsorbentes en técnicas en flujo sin problemas de aglomeración ni aumento de la sobrepresión en el sistema automático. Para demostrar el potencial analítico de este método se analizaron trazas de herbicidas de la familia de las clorotriazinas (atrazina, simazina y propazina) y sus metabolitos (desisopropiltriazina (DIA) y desetilatrazina (DIA) en aguas y extractos de suelos previa preconcentración por μSPE. En el capítulo 9 titulado: “Acoplamiento en-línea de bead-injection-Lab-on-Valve a cromatografía de gases (BI-LOV-GC). Aplicación a la determinación de niveles traza de bifenilos policlorados (PCBs) en lixiviados de residuos sólidos” se propone por primera vez en la bibliografía el acoplamiento de plataformas mesofluídicas con μSPE renovable a GC para la monitorización de contaminantes orgánicos. Mediante este nuevo método se determinaron PCBs en lixiviados crudos de residuos en vertederos previa extracción y concentración automática seguida de separación por GC.
Automatic sample preparation methods are nowadays imperative to meeting compressed analytical timeline. As a result, mechanized sample preparation methods hyphenated with analytical techniques exploiting the different generations of flow analysis were in this dissertation developed and characterized for determination of organic and inorganic pollutants in environmentally relevant samples and industrial wastes. The thesis consists of two parts; the first is devoted to the development of automatic methods for dynamic chemical fractionation and investigation of bioaccessibility of inorganic trace contaminants in solid samples including coal fly ash and biomass fuels. The second part involved the development of automatic sorptive methods prior to chromatographic assays for extraction, preconcentration, separation and determination of trace concentration levels of selected pesticides (namely, triazine and metabolites thereof, and polychlorinated biphenyl compounds (PCBs)) in environmental samples at levels below those endorsed in current Directives. Dynamic flow-through fractionation is proven to afford more accurate evaluation of potentially bioaccessible metal pools under environmentally changing conditions than the equilibrium-based counterparts as a consequence of the solid/liquid equilibria shift and absence of metal redistribution effects. In fact, natural processes are occurring under dynamic rather than static conditions as assumed in classical methods. In this context, a novel miniaturized flow-based configuration capitalized on stirred-flow cell extraction was devised for automatic assessment of bioaccessible pools of trace metals (namely, Cu, Cd, Ni, Pb and Zn) in three samples at a time with no limitation of sample amount up to 1.0 g. A two-step sequential extraction scheme involving water and acetic acid (or acetic acid/acetate buffer) was utilized for reliable estimation of readily mobilisable fractions of trace elements in fly ash under worst-case conditions following the US-Toxicity Characteristic Leaching Test (TCLP), the results of which are reported in chapter 3 entitled “Multiple stirred-flow chamber assembly for simultaneous automatic fractionation of trace element in fly ash samples using a multisyringe-based flow system”. In dynamic extraction approaches, the solid sample under investigation is loaded into a suitable container, and exposed continuously to fresh extractant volumes by resorting to flow-based approaches. In this thesis, two dynamic extraction systems, the so-called sequential injection microcolumn extraction (SI-MCE) and sequential injection stirred-flow chamber extraction (SI-SFCE) were critically compared on the basis of the sample-containing container, sample representativeness, homogeneity of the sample, and analytical results aimed at further harmonization of this novel leaching methodology. The three-step EU approved BCR sequential extraction scheme was performed in both automatic dynamic fractionation systems to evaluate the extractability of Cr, Cu, Ni, Pb and Zn in a standard reference material of coal fly ash (NIST 1633b) as detailed in chapter 4 entitled “Critical evaluation of novel dynamic flow-through methods for automatic sequential BCR extraction of trace metals in fly ash”. On-line coupling of SI-SFCE with ICP-OES was resorted to the exploration of the potential availability of ash-forming elements (e.g., K, Ca, Na and Mg) of biomass fuels (namely, bark and twigs) in flue gases, which is regarded as indicative of potential fireside problems (fouling and slagging in combustion devices). Experimental results are compiled in chapter 5 entitled “Automated dynamic chemical fractionation method with detection by plasma spectrometry for advanced characterization of solid biofuels”. The ultimate aim is to have a reliable system at hand to assist in deciding on a short notice whether or not firing biomass fuels on the basis of potential corrosion risks in combustion devices. For elucidation of metal-biomass/ash associations and investigation of the actual selectivity of extractants, dynamic extraction data was judiciously combined with spectroscopic characterization techniques, namely, scanning electron microscopy with energy dispersive X-ray fluorescence spectrometry (SEM-EDX) and X-ray diffraction (RXD) assays. These studies are shown in chapter 6 entitled “Elucidation of associations of ash-forming matter in woody biomass residues”. In the second part of the thesis, automatic sample preparation methods have been developed using solid-phase extraction (SPE) approaches in flowing stream systems as a “front end” to chromatography techniques (GC or LC). Selective μSPE in a Bead-Injection (automatic renewable SPE) mode in the so-called multi-dimensional SPE combining molecular imprinted polymers (MIP) and reversed-phase sorbents (Oasis HLB) was utilized in Chapter 7 (Multimodal bead injection-based flow-through microextraction involving renewable molecularly imprinted and reversed-phase sorbents as a front end to liquid chromatography for automatic multiresidue assays) for selective preconcentration of triazine residues and their metabolites in crude soil extracts. The hyphenated μSPE-HPLC system was proven to provide sufficient sensitivity and reliability for determination of the target herbicides (namely, atrazine, simazine and propazine) and their dealkylated metabolites (namely, deisopropyltriazine (DIA) and deethylatrazine (DEA)) at concentration levels below those specified by current legislations for human water consumption and surface waters. In chapter 8 entitled “Flowthrough dispersed carbon nanofiber-based microsolid-phase extraction coupled to liquid chromatography for automatic determination of trace levels of priority environmental pollutants” dispersed carbon nanomaterials were handled as sorptive surfaces in an automatic flow-mode with minimum nanoparticle agglomeration and negligible pressure drop. The proof-of-concept of the method was demonstrated for μSPE and clean-up of chlorotriazine residues (namely, atrazine, simazine and propazine) and their dealkylated metabolites (namely, deisopropyltriazine (DIA) and deethylatrazine (DEA)) in both environmental waters and soil extracts. In Chapter 9 entitled “On-line coupling of bead injection-lab on valve analysis to gas chromatography (BI-LOV-GC). Application to the determination of trace levels of polychlorinated biphenyls (PCBs) in solid waste leachates” is for the first time demonstrated the coupling of mesofluidic platforms with renewable μSPE to GC for monitoring of organic pollutants. This new approach fostered the isolation, concentration, separation and determination of PCBs from raw landfill leachates.

Food additives, drugs and growth-enhancing compounds are prominent tools in the production of sufficient quantities of affordable food. Thus, food safety has become a main concern of many countries for protection of their population's health. Analytical chemical measurements are increasingly important to ensure consumer protection, particularly in the field of antibiotic residues. International comparability and reliability of measurement results can be achieved by establishing and demonstrating the metrological traceability of those results to the International System of Units (SI). To ensure the metrological traceability of measurement results, reference methods and certified reference materials (CRMs) are needed. Nitrofuran antibiotic drugs used for the treatment of bacterial and protozoan infections in animals were studied in this thesis. A high accuracy reference method and an appropriate CRM for the detection of nitrofurans in prawns have been developed. A reference method for the measurement of mass fractions of nitrofuran metabolites 3-amino-5-methyl-morpholino-2-oxazolidinone (AMOZ), 3-amino-2-oxazolidinone (AOZ), semicarbazide (SEM) and 1-aminohydantoin (AHD) has been developed utilising an exact matching double isotope dilution mass spectrometry (IDMS) method. A feasibility study on a fortified reference material was carried out by preparing fortified samples containing the four nitrofuran metabolites. The stability testing results showed that the analytes in the freeze-dried matrix were more stable than in the wet form. Freeze-dried certified reference materials of nitrofurans in prawns have been produced; an incurred AOZ (CRM_P1) and incurred AOZ and fortified SEM (CRM_P2). The reference method developed was applied for the characterisation of certified reference materials for homogeneity, stability study and certification. The prepared certified reference materials were found to be homogeneous and remained stable under normal transport conditions. The measurement uncertainty of the measurement results obtained by the reference method developed was determined by thoroughly examining all possible sources of potential bias and precision effects. An initial measurement uncertainty for certified values of AOZ in both materials has also been estimated. Metrological traceability of measurement results obtained by the developed reference method and the reference value of the prepared certified reference materials has been established through the use of the traceable primary ratio method of exact matching double IDMS, the use of certified nitrofuran metabolite standards, and gravimetric preparation of samples.

A primary objective of the effort reported here is to develop a radiometric instrument modeling environment to provide complete end-to-end numerical models of radiometric instruments, integrating the optical, electro-thermal, and electronic systems. The modeling environment consists of a Monte Carlo ray-trace (MCRT) model of the optical system coupled to a transient, three-dimensional finite-difference electrothermal model of the detector assembly with an analytic model of the signal-conditioning circuitry. The environment provides a complete simulation of the dynamic optical and electrothermal behavior of the instrument. The modeling environment is used to create an end-to-end model of the CERES scanning radiometer, and its performance is compared to the performance of an operational CERES total channel as a benchmark. A further objective of this effort is to formulate an efficient design environment for radiometric instruments. To this end, the modeling environment is then combined with evolutionary search algorithms known as genetic algorithms (GA's) to develop a methodology for optimal instrument design using high-level radiometric instrument models. GA's are applied to the design of the optical system and detector system separately and to both as an aggregate function with positive results.
Ph. D.

To compare the effect of a standard commercial trace mineral dietary program to low levels of organic minerals on turkey performance, mineral excretion, bone strength, and carcass yield, day-old Hybrid poults (n=1,224) were randomly distributed to one of four treatments with 9 replicates. Experimental treatments consisted of: standard inorganic (SI) with a commercial supplementation program (Mn, Zn, Cu, Se), reduced inorganic (RI) with 10% level of SI, and two organic regimens of Bioplex®/Sel-Plex® (at the same level of RI during period 1 and 2 and at 2/3 of RI for period 3, 4, 5, and 6, or at the same level of RI for entire trial). Body weight (BW), body weight gain (BWG), feed conversion ratio (FCR), and feed intake (FI) were evaluated and fresh excreta were collected at d 28, 49, 70, 84, 105 and 133. Tibias and femurs were collected at d 49, 84 and 133. Trace mineral concentration in litter and carcass yield were determined at d 133. Overall, there was no significant effect on BW, cumulative BWG, FCR, or FI due to treatments (P < 0.05). The contents of Mn and Zn in excreta and litter were significantly reduced (P < 0.05) in Bioplex®/Sel-Plex® or RI diet compared to SI during the study. Cu excretion was significantly reduced at d 84 and 133. Tibias from the SI treatment had increased bone strength at d 49. Carcass yield at processing was significantly improved (P < 0.05) by feeding Bioplex®/Sel-Plex® treatments compared to the SI diet. To investigate the effect of organic or inorganic Zn combined with other trace minerals on turkey performance, immune response, and intestinal development, a 2 by 4 factorial design was utilized with coccidia vaccinated and non-vaccinated and 4 dietary treatments varying in level and source of Zn with Mn, Cu, and Se. A total of 2,376 day-old Hybrid turkeys were assigned to one of the combinations with 9 replicates of each. Dietary treatments consisted of: 1) standard inorganic (SI), Zn (150 ppm) with Mn (165 ppm), Cu (10 ppm), and Se (0.2 ppm); 2) reduced inorganic (RI), Zn, Mn, and Cu at 10% of SI, and Se at 0.2ppm; 3) organic 1 (O1), at the same level of RI; 4) organic 2 (O2), Zn (30 ppm) with the same level of Mn, Cu, and Se as O1. Body weight, BWG, FI and FCR were determined weekly. Bursa, thymus, and spleen were weighed, and duodenum and jejunum were collected at d 7, 14, 28, and 42. Peripheral blood was collected for T-lymphocyte populations on d 21, 28, and 42. Cumulative FI was influenced by vaccination (P=0.003). Cumulative BWG and BW were significantly decreased by vaccination except on d 14. Cumulative BWG increased in poults fed RI compared with those fed O2 (P=0.03). Poults fed O2 had significantly decreased BW when compared with RI after d 28. Cumulative FCR was not affected by diet and vaccination. Vaccination increased spleen weight on d 7 and thymus weight on d 42 (P < 0.05). The birds fed O2 had increased thymus weight when compared with those fed SI at d 7 (P < 0.05). The vaccinated poults had higher numbers of CD4+ T-cells than non-vaccinated birds on d 28 and d 42 (P < 0.05), and an interaction between diet and vaccination was observed (P < 0.05). Compared to non-vaccinated poults, CD4+/CD8+ ratio was significantly increased in vaccinated poults on d 42 (P = 0.0475). The villus height in vaccinated birds was significantly increased in the jejunum (P = 0.0012), but diets did not affect intestinal morphology. In summary, using low levels of organic or inorganic trace minerals is adequate to maintain turkey performance and immune response and decreased trace minerals excretion.
Ph. D.

Radioactive isotopes are present at some level in all materials in our environment. Detection of these isotopes by conventional means can be difficult if they decay very slowly (have a long half-life). Accelerator Mass Spectrometry (AMS) systems are actually designed to measure extremely low levels or such isotopes. Such measurements are often useful for dating geological processes and archaeological artifacts or tracing chemical pathways through complex systems. In the search for very rare processes such as neutrinoless double beta decay, the presence of very low levels of radioactive material can interfere with the measurement process. Therefore, materials used to build the experimental equipment have to contain as few radioactive isotopes as possible. Neutrinoless double beta decay (NDBD) is of interest for understanding whether the neutrinos are Dirac or Majorana particles. SNO+ and nEXO are among the experiments at SNO Lab, located in Sudbury, Canada for the detection of neutrinos and other extremely weak physical processes. The SNO+ detector is a large 12m diameter spherical scintillation counter which will be able to study low energy solar, geo- and reactor neutrinos, as well as being able to conduct supernova searches. This detector was built with materials with very low radioactivity such as the organic liquid, Linear Alkyl Benzene (LAB), the scintillation fluid in which the radioactivity was measured in earlier scintillation detectors. For NSBD measurements, the SNO+ experiment will add tellurium-130 to the LAB; In order to fully mix the 130Te into the LAB, the liquid 1, 2 Butanediol has been selected as a chelating agent to which the atoms of 130Te can be added. This project describes the measurement of the 14C content of the 1, 2 Butanediol which confirmed its suitability for use in the NDBD experiment. nEXO is the next in a series of experiments dedicated to the search for NDBD in Xenon-136. The nEXO detector is a time projection chamber (TPC) filled with 5000 kg of liquid Xe. One major source of reduction in sensitivity of this detector is the radioactive decay of trace amounts of uranium and thorium isotopes naturally present the construction materials. In order to assess the quantity of these isotopes in the copper used to make the electrodes in the TPC, samples of the copper to be used in the chamber were analyzed using AMS. In this measurement, a better source of copper was found.

As part of the INTAS funded CLIMAN project into Holocene climatic variability and the evolution of human settlement in the Aral Sea basin, fossil diatoms obtained from Chernyshov Bay in the Aral Sea have been examined in order to reconstruct conductivity and lake level change since ca. 400 AD. In an effort to establish whether fluctuations in lake level are a result of natural climatic variation or human activity across the region, the values of 613C of organic material (8I3Corg) have also been determined. The extent of anthropogenic impact on the lake has also been assessed by ascertaining the history of trace metal (Cd, Pb and Hg) contamination. Palaeoconductivity has been derived using the EDDI diatom-conductivity transfer function. Results indicate a waterbody that fluctuates between fresh and oligosaline conditions which is punctuated by three phases of elevated conductivity, all within the mesosaline range and corresponding low lake levels at ca. 400 AD, ca. 1195 - 1355 AD and ca. 1780 AD to the present day. These regressions are confirmed by diatom habitat requirements, where, due to the morphology of the lake, planktonic species are indicative of regressive phases. The C/N ratio of organic material (< 10) throughout the core indicates that 8,3Corg provides a record of within lake productivity rather than switches of vegetation in the lake's catchment. The highest values are seen to correspond with high diatom inferred conductivity and low lake levels, due to increased salinity, residence time and algai productivity. This suggests that the severity of the observed lake level changes were a result of the natural diversion of the principal source of the lake's hydrological inputs, the Amu Darya river and anthropogenic activity in the form of irrigation, social upheaval and military conflict. Since 400 AD, the trace metal record from Chernyshov Bay indicates no local or long range anthropogenic contamination of Pb and Hg. Increases of Cd over the last ca. 100 years may be related to increased fertilizer application in tandem with increased cultivation in the region.

La dependencia de datos es una de las principales razones que limitan el rendimiento de los procesadores actuales. Algunos estudios han demostrado, que las aplicaciones no pueden alcanzar más de una decena de instrucciones por ciclo en un procesador ideal, con la simple limitación de las dependencias de datos. Esto sugiere que, desarrollar técnicas que eviten la serialización causada por ellas, son importantes para acelerar el paralelismo a nivel de instrucción y será crucial en los microprocesadores del futuro.
Además, la innovación y las mejoras tecnológicas en el diseño de los procesadores de los últimos diez años han sobrepasado los avances en el diseño del sistema de memoria. Por lo tanto, la cada vez mas grande diferencia de velocidades de procesador y memoria, ha motivado que, los actuales procesadores de alto rendimiento se centren en las organizaciones cache para tolerar las altas latencias de memoria. Las memorias cache solventan en parte esta diferencia de velocidades, pero a cambio introducen un aumento de área del procesador, un incremento del consumo energético y una mayor demanda de ancho de banda de memoria, de manera que pueden llegar a limitar el rendimiento del procesador.
En esta tesis se proponen diversas técnicas microarquitectónicas que pueden aplicarse en diversas partes del procesador, tanto para mejorar el sistema de memoria, como para acelerar la ejecución de instrucciones. Algunas de ellas intentan suavizar la diferencia de velocidades entre el procesador y el sistema de memoria, mientras que otras intentan aliviar la serialización causada por las dependencias de datos. La idea fundamental, tras todas las técnicas propuestas, consiste en aprovechar el alto porcentaje de repetición de los programas convencionales.
Las instrucciones ejecutadas por los programas de hoy en día, tienden a ser repetitivas, en el sentido que, muchos de los datos consumidos y producidos por ellas son frecuentemente los mismos. Esta tesis denomina la repetición de cualquier valor fuente y destino como Repetición de Valores, mientras que la repetición de valores fuente y operación de la instrucción se distingue como Repetición de Computaciones. De manera particular, las técnicas propuestas para mejorar el sistema de memoria se basan en explotar la repetición de valores producida por las instrucciones de almacenamiento, mientras que las técnicas propuestas para acelerar la ejecución de instrucciones, aprovechan la repetición de computaciones producida por todas las instrucciones.
Data dependences are some of the most important hurdles that limit the performance of current microprocessors. Some studies have shown that some applications cannot achieve more than a few tens of instructions per cycle in an ideal processor with the sole limitation of data dependences. This suggests that techniques for avoiding the serialization caused by them are important for boosting the instruction-level parallelism and will be crucial for future microprocessors.
Moreover, innovation and technological improvements in processor design have outpaced advances in memory design in the last ten years. Therefore, the increasing gap between processor and memory speeds has motivated that current high performance processors focus on cache memory organizations to tolerate growing memory latencies. Caches attempt to bridge this gap but do so at the expense of large amounts of die area, increment of the energy consumption and higher demand of memory bandwidth that can be progressively a greater limit to high performance.
We propose several microarchitectural techniques that can be applied to various parts of current microprocessor designs to improve the memory system and to boost the execution of instructions. Some techniques attempt to ease the gap between processor and memory speeds, while the others attempt to alleviate the serialization caused by data dependences. The underlying aim behind all the proposed microarchitectural techniques is to exploit the repetitive behaviour in conventional programs.

Instructions executed by real-world programs tend to be repetitious, in the sense that most of the data consumed and produced by several dynamic instructions are often the same. We refer to the repetition of any source or result value as Value Repetition and the repetition of source values and operation as Computation Repetition. In particular, the techniques proposed for improving the memory system are based on exploiting the value repetition produced by store instructions, while the techniques proposed for boosting the execution of instructions are based on exploiting the computation repetition produced by all the instructions.

The purpose of this thesis is to further develop numerical methods for solving surface problems by utilizing tangential calculus and the trace finite element method. Direct computation on the surface is possible by the use of tangential calculus, in contrast to the classical approach of mapping 2D parametric surfaces to 3D surfaces by means of differential geometry operators. Using tangential calculus, the problem formulation is only dependent on the position and normal vectors of the 3D surface. Tangential calculus thus enables a clean, simple and inexpensive formulation and implementation of finite element methods for surface problems. Meshing techniques are greatly simplified from the end-user perspective by utilizing an unfitted finite element method called the Trace Finite Element Method, in which the basic idea is to embed the surface in a higher dimensional mesh and use the shape functions of this background mesh for the discretization of the partial differential equation. This method makes it possible to model surfaces implicitly and solve surface problems without the need for expensive meshing/re-meshing techniques especially for moving surfaces or surfaces embedded in 3D solids, so called embedded interface problems. Using these two approaches, numerical methods for solving three surface problems are proposed: 1) minimal surface problems, in which the form that minimizes the mean curvature was computed by iterative update of a level-set function discretized using TraceFEM and driven by advection, for which the velocity field was given by the mean curvature flow, 2) elastic membrane problems discretized using linear and higher order TraceFEM, which makes it straightforward to embed complex geometries of membrane models into an elastic bulk for reinforcement and 3) stabilized, accurate vertex normal and mean curvature estimation with local refinement on triangulated surfaces. In this thesis the basics of the two main approaches are presented, some aspects such as stabilization and surface reconstruction are further developed, evaluated and numerically analyzed, details on implementations are provided and the current state of work is presented.

This is the first study to compare total arsenic (As) and other trace elements in the agricultural soils and grain of Eastern, Western and Southern Libya, North Africa and the Middle East (NA & MIDEA). Soil pot experiments and field experiments were conducted to determine the levels of As within wheat grains in Libya. In the soil pot experiments, wheat genotypes were planted in similar soils and yet differences in grain As concentration were found among the cultivars. The highest As accumulation was found in T. durum; however, in the field data the highest levels were found in T. aestrivum. The levels of As and other trace elements found in agricultural soils from the Eastern Western and Southern regions of Libya are examined. Mean As concentrations in the clay mineral agricultural soils of the Eastern Region were nearly 4.8 and 4.1 times higher than in the southern and western regions, respectively. It is possible that the parent material of that region contains elevated levels of As, which are then exhibited in the overlying soil. Differences in the levels of As and other trace elements found in the irrigated agricultural soil of Southern Libya were compared with non-irrigated soil from the same region.  Concentrations of P, Zn and As in soil were higher in irrigated compared to non-irrigated soils, while the concentration of Cd is nearly the same in all soil samples. A market basket investigation was conducted to determine the total levels of As and Se in rice purchased from supermarkets. The average level of As in rice from NA & MIDEA is 0.22 mg/kg, comparable with average levels in Australia.

This thesis explores the participation of women in trade union activity at local level. The central question it addresses is why do women participate in trade unions at this level? It identifies the factors that shape and influence women's participation and, in particular, the role of gender. In addition the thesis critically exatnines the concept of women's interests. The methodological approach is that of a case study of women activists in the South Wales and Western division of the Union of Shop, Distributive and Allied Workers (USDA W), and a principal case study of women activists in the South and West area of the Banking, Insurance and Finance Union (BIFU). In recent years there has been a growing body of research considering the role of women in trade unions. The main focus of these studies has been the barriers to women's participation. Where women's participation has been investigated the majority of studies have been concerned with women full time officers and 'senior' trade union leaders. Within trade union renewal debates women have been highlighted as one of the groups to target in recruitment campaigns. As such, it is appropriate to consider women's trade union participation at local level. The general literature suggests that people join and participate for traditional collective reasons. This proposition is critically examined. The findings present a model of trade union activity that differs significantly from typologies created to examine 'senior' women leaders. Equally, studies of women at local level which attach one ideological position to women's attitudes and behaviour are argued to fail to capture the diversity of views evident at local level. As such, the typology developed from this study places the WOlnen activists in four groups; the individualist, the collectivist, the carer and the equal rights representative. These groups reflect the context in which the women are situated and the varied interpretations of their activism. The findings suggest the problems of addressing equal opportunities through the union structures and raise, in particular, the difficulties of developing 'separatist' policies for women. Barriers to women's participation in trade unions remain significant for local level activism. The thesis suggests that trade union renewal strategies need to recognise the richness and diversity of attitudes and interests that women bring to the trade union movement.

Trade unions are juristic entities and volitional associations that have, historically and ideologically, represented the aggregate strength of labour to maximise their effectiveness in their endeavour to fulfil their core responsibilities and principal functions. However, Ceronie (2007) postulates that, in South Africa, there has been a loss of ideological support for unions since the dawn of democracy. The establishment of the democracy had the effect that a huge driving gear to belong to a union was lost. The mandate of trade unions is to, inter alia, protect, maintain, and improve the working conditions of their members. They fulfil this mandate by ensuring that they offer services that meet, if not exceed, members' satisfaction levels. Trade unions ultimately exist to protect both the work- and non-work-related interest of their members, whether these be economic, social, political, or environmental (Venter, 2003). Nel et al. (2005) asseverate that trade unions are membership organisations: They exist because of their members, they are made up of members, they serve their members' interest, and they are governed by their members. That is, they derive their authority and mandate from the members. Therefore, trade union are service providers. They must give employees enough reason to become attracted to them as members and to remain members. Simply put, trade unions, as the embodiment of workers' aspirations, owe a duty of care to their members, and thus should at all times, act in their best interests. Thus, the kind and quality of services offered by trade unions should be perceived by members as sufficient and satisfactory. Highly satisfied and committed union members are more likely to support and participate in trade union activities. Trade unions, like any other organisation that provides services, are faced with challenges of membership decline due to perceived poor services or the lack thereof, and are therefore required to devise remedial measures to mitigate the membership decline. Against the backdrop of the foregoing, the aim of the study was to examine if there is a relationship between the quality of services and benefits offered by unions to their members and member satisfaction. The sample comprised members of the three major unions within the public service of South Africa. Using the quantitative paradigm, primary empirical data were collected by distributing 500 questionnaires, which yielded a 48.9% response rate. Data were analysed using the SPSS Statistics 23 software program. The questionnaire was valid and reliable, with an overall scale reliability coefficient of α = .975. The findings revealed moderate levels of member satisfaction (56%) with low dissatisfaction (16%), and a significantly high participation rate in union activities (61%), and union effectiveness (80%). That is, the findings revealed that members were generally satisfied with their unions' performance. The findings affirm union instrumentality, union effectiveness, and member participation as antecedents of union commitment, and also confirm unions' performance and effectiveness as significant determinants of members' satisfaction with a union. Therefore, in a quest to maintain and/or increase their relevance, trade unions must examine their current services and benefits, in order to determine whether they still meet their members' preferences, and, if not, to develop and provide a new service mix that will not only appeal to unionised members, but will also attract non-unionised workers.
Thesis (PhD)--University of Pretoria, 2017.
Human Resource Management
PhD
Unrestricted

This dissertation addresses specific issues on domestic and foreign trade in India. The three chapters of the dissertation are summarized as follows. In the first chapter, we analyze the existence of regional wage differences across Indian states, and how domestic trade affects those premiums. We follow a two-step estimation process used in the literature on Labor Economics. Our empirical results show that higher level of domestic imports tends to reduce the state premiums, and higher domestic exports increase those premiums, which is consistent with a specific factor Ricardo-Viner model. Thus, promoting domestic trade by with states specializing in certain industries may lead to higher welfare within the country. In addition, we find, state premiums depend negatively on state-level amenities measured by per-capita power availability, and does not depend on the richness of the State measured by per-capita Net State Domestic Product. In the second chapter, we look at the pattern and determinants of inter-state manufacturing trade in India. In the paper, we use information on 12 manufacturing industries categorized under 5 sectors from 2005 to 2013 with two-year intervals in between. We find that a 1\% decrease in income ratio between importing state net state domestic product and exporting state net domestic product has significantly varying effects on trade flows across the different sectors. For coal and minerals, the effect is 36.8%, for chemical it is 105%, for metals it is 31.5% and for cement, it is 36.8%. In all these case a decrease in income ratio increases exports. For machinery, a 1% decrease in income ratio lead to approximately 9.3% reduction in trade. This suggests that machineries which are capital goods are more imported by richer states, whereas the other goods which can be classified as intermediate inputs are more imported by poorer states. We also find that infrastructure promotes trade and on average infrastructure reduces the effect of contiguity by around 28.6% and promotes trade even between non-contiguous states. Therefore, infrastructure in the form of roadways, highways, and railways must be built and maintained to promote facilitate trade in India. In chapter three, we compare the effects of tariffs and non-tariff barriers on Indian exports. We use Indian HS-96 four-digit industry level export data from COMTRADE and tariff data from TRAINS database for the study. The overall result suggests that input tariffs have the largest effect on exports, followed by final tariff and foreign tariffs. A 1% reduction in input tariff leads to around 8.6% increase in exports. A similar reduction in final tariffs and foreign tariffs lead to 3.6% and 2.8% increase, respectively in exports. Thus, we conclude that the supply side effect of exports dominates the demand side effects. From a policy perspective, if countries try to improve trade balance by imposing high tariffs, it may lead to a negative effect on exports through the input tariff effects.

Thesis (M.A. in National Security Affairs)--Naval Postgraduate School, March 2006.
Thesis Advisor(s): Harold Trinkunas. "March 2006." Includes bibliographical references (p. 63-71). Also available online.

As the demand for feature-rich portable devices continues to increase, new techniques are needed to minimise power consumption. This thesis is concerned with the development and validation of new systematic architectural methods of determining pipeline stage insertion in data-dominated designs with the aim of reducing dynamic power consumption. The methods place special emphasis on the number of latches used in pipeline stages and voltage scaling. The first part of the thesis addresses power:minimisation through systematic analysis of the number of latches in pipeline stages. A new pipeline stage insertion (PSI) method operating at the architectural level is developed which takes into account system clock period and FEs outputs and delays. A PSI algorithm based on analytical heuristic equations is formulated to ensure the successful application of this method to any given data-dominated design. The input to the algorithm 'is designer clock period and naively inserted pipeline stages. The output from the algorithm is a pipelined design fulfilling the timing constraint with the least dynamic power consumption. To support efficient power-performance trade-offs exploration, the algorithm was fully automated. The second part of the thesis focuses on the validation of the PSI method using two real-life case studies: triple data path floating-point adder· and MPEG-I motion compensation module. These designs are common in many portable devices and have numerous implementation challe·nges including large number of FEs and significant power consumption. Extensive experimental results show that for the motion compensation module, the PSI is able to reduce dynamic power consumption by up to 30% compared with other reported approaches. The final part of the thesis concentrates on voltage scaling (VS) and its impact on pipeline stages. The timing slack available in each stage is investigated, with the aim of further reducing power consumption by lowering the supply voltage. The PSI method is modified to support voltage scaling, and as a result, a new pipeline stage insertion with voltage scaling (PSI-VS) method is proposed. Experimental results show that the PSI-VS can lead to significant power saving compared with PSI without VS. For the MPEG-I motion compensation case study, a power saving of 68% is observed. All the developed methods have linear time complexity as the number of pipeline stages increases, facilitating their application to large designs without incurring run time penalty. The results for the case studies were based on a synthesisable RTL implementation using 90nrn technology together with accurate power analysis using commercial tools.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (March 1, 2006) Vita. Includes bibliographical references.

Trace element levels (B, V, Cr, Mn, Fe, Cu, Zn, As, Sr and Cd) in environmental (water and cigarette tobacco) and biological (tear drop, saliva, scalp hair and fingernail) samples collected from Iraqi individuals resident in Karbala (Iraq) and London (UK) were determined by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP- AES). Multi-element analysis was carried out on drinking (commercial, domestic bottled and tap) and irrigation (river, artesian and well) water samples. It was found that most trace element levels (ug/l) were lower than the permissible guidelines for drinking water recommended by the World Health Organisation (WHO) and Iraqi government. The only exceptions were for B in artesian and well waters; and Cd in river, artesian and well waters. The highest levels in drinking and irrigation waters were found for Sr when compared with other trace elements. Trace element levels in tap water from Karbala were higher than those from London. The levels of trace elements in cigarette tobacco were found to be at higher to lower levels through the following sequence: Fe> Mn > Sr> Zn > Cu > As > Cd > Cr > V. Moreover, multi-element analysis was undertaken for tear drop, saliva, washed scalp hair and fingernail samples for Iraqi individuals from Karbala (Iraq) and London (UK). Discriminant analysis suggested that Sr, Mn, B, V, As, Cd and Zn levels could be used to discriminate between healthy and diabetic populations (83% of cases correctly classified). Higher trace element levels were found in the tear drop, saliva, scalp hair and fingernail samples from Karbala than those from London. The influence of various factors (health status, gender and smoking activity) and covariates (individual's age and drinking water) on elemental levels in tear drops was investigated using the analysis of covariance (ANCOV A). Significant differences (at P < 0.05) were found between the healthy and diabetic individuals for B, Mn and Sr; males and females in terms of the levels of Fe; and smokers and non-smokers for Cd. Trace element levels in drinking water were found to have significant effects on the levels of V, Mn and Sr, whilst an individual's age has a significant effect in terms of Zn and As. Inter- element interactions were evaluated for each pair of trace elements in tear drops, and between tear drops and saliva, washed scalp hair and fingernails. There were 32 and 27 statistically significant correlations of the total 45 tested using tear drops from healthy and diabetic individuals, respectively. Similar results were observed for saliva, washed scalp hair and fingernails in terms of residential location, health status and inter-element interactions. The use of tear drops as a potential biomarker for assessing human health status has been evaluated using several studies in this research, namely; drinking water analysis, smoking activity and type 2 diabetes.

Institutions, and their underlying rules, are essential for economic development, in that they provide a framework for markets to operate. However, different types of regulatory roles and even institutional settings may have very different effects on outcomes at the firm or individual level. This dissertation examines the effect of several types of rules and institutions on productivity and related measures. The first chapter examines the effect of international competition and domestic competitive barriers on firm-level productivity growth in the OECD. A close interaction is observed between import penetration and domestic barriers to entry, conditional on a firm's distance to the technological frontier. The second chapter examines the effects of labor market reform on plants in different Indian states. A positive effect of labor market reform is found on plant-level productivity growth in labor-intensive and volatile industries. The third chapter looks at Indian exporters who took advantage of capital account liberalization to invest abroad, and explores whether they gained through learning-by-doing. After matching these firms with similar firms that did not invest abroad, the chapter finds that productivity was not boosted, though firms did gain in terms of their overall size through market access. The fourth chapter explores how the legal system in different Mexican states has impacted the size of firms through heightened capital intensity. States with higher quality legal institutions are found to have systematically larger and more productive firms.

Maintenance management decision-support systems are needed to help senior decision-makers and asset managers to better plan timely and efficient maintenance. Within the railway industry, several maintenance management decision-support systems have been developed. However, most these operate at project level where decisions are limited to short sections of track. Network level maintenance management systems enable future prediction of the condition of the railway network under different allocation of resources in a manner to provide acceptable levels of safety, reliability and cost. This project describes the development of a theoretical framework for the strategic assessment of network level railway maintenance funding and policy decisions. The model is designed to aid railway asset managers in planning medium to long-term maintenance investment requirements for the railway network. The model is based on stochastic processes which are capable of determining the effects of traffic, maintenance and climate on network condition under any budget scenario.

Les institutions et leurs règles sous-jacentes sont essentielles pour le développement économique, car elles fournissent un cadre pour le bon fonctionnement des marchés. Cependant, les différents types de réglementations et même les cadres institutionnels peuvent avoir des effets très différents sur les résultats au niveau de l'entreprise ou de l'individu. Cette dissertation examine l'effet de plusieurs types de règlementations et d'institutions sur la productivité et des mesures apparentées à celle-ci. Le premier chapitre examine l'effet de la concurrence internationale et des barrières compétitives intérieures sur la croissance de la productivité au niveau de l'entreprise dans les pays de l'OCDE. Une interaction étroite est observée entre la pénétration des importations et les obstacles à l'entrée d'origine nationale, conditionnelle à la distance où se trouve une entreprise par rapport à la frontière technologique. Le deuxième chapitre examine les effets de la réforme du marché du travail dans les usines situées dans les différents états de l'Inde. Un effet positif de la réforme du marché du travail est observé sur la croissance de productivité au niveau de l'entreprise dans les industries à forte intensité de main-d'œuvre et les industries volatiles. Le troisième chapitre se concentre sur les exportateurs indiens qui ont profité de la libéralisation des capitaux pour investir à l'étranger et cherchent à savoir s'ils ont profité grâce à l'apprentissage par la pratique. Après avoir fait correspondre ces entreprises avec des entreprises semblables mais qui n'ont pas investi à l'étranger, le chapitre montre que la productivité n'a pas été stimulée, bien que les entreprises aient vraiment gagné en termes de taille globale grâce à l'accès au marché. Le quatrième chapitre explore comment la qualité du système juridique dans les différents États du Mexique a eu un impact sur la taille des entreprises. Les états pourvus de meilleures institutions juridiques apparaissent comme ayant des entreprises avec un capital plus grand, plus intense et étant plus productives
Institutions, and their underlying rules, are essential for economic development, in that they provide a framework for markets to operate. However, different types of regulatory roles and even institutional settings may have very different effects on outcomes at the firm or individual level. This dissertation examines the effect of several types of rules and institutions on productivity and related measures. The first chapter examines the effect of international competition and domestic competitive barriers on firm-level productivity growth in the OECD. A close interaction is observed between import penetration and domestic barriers to entry, conditional on a firm's distance to the technological frontier. The second chapter examines the effects of labor market reform on plants in different Indian states. A positive effect of labor market reform is found on plant-level productivity growth in labor-intensive and volatile industries. The third chapter looks at Indian exporters who took advantage of capital account liberalization to invest abroad, and explores whether they gained through learning-by-doing. After matching these firms with similar firms that did not invest abroad, the chapter finds that productivity was not boosted, though firms did gain in terms of their overall size through market access. The fourth chapter explores how the legal system in different Mexican states has impacted the size of firms through heightened capital intensity. States with higher quality legal institutions are found to have systematically larger and more productive firms

Trace amounts of germanium is determined by flame atomic absorption spectrometry by utilizing the vaporization of germanium tetrachloride. Using a continuous flow reactor, sample solution is mixed with concentrated hydrochloric acid and heated to 80º
C to form volatile germanium tetrachloride which can be subsequently sent to N2O-C2H2 flame AAS. The necessary conditions for the volatilization of germanium tetrachloride are investigated in detail and the applicability of the method for the determination of trace amounts of germanium in real samples and standard reference materials are presented. Detection limit of the method, based on 3s, was 0.034 ng mL-1 using a sample of 1 mL. The precision was 0.3 %, expressed as the relative standard deviation for a germanium concentration of 1 ng mL-1. Owing to the high selectivity of the proposed method, no interference effect was observed.

In an open economy economic agents distribute their spending between domestic and various import goods and they may reconsider their choice whenever relative international prices change. Armington elasticities quantify these reallocations in demand for goods produced in different countries. Recent analytical frameworks allow to further differentiate between a macro elasticity of substitution between domestic and import goods and a micro elasticity between different import sources. Despite the relevance of Armington elasticities for evaluating trade policy there has been no systematic study on whether micro and macro elasticities significantly differ for highly integrated economies within a free trade area and whether there is a common pattern. Using highly disaggregated data, this paper estimates Armington elasticities for a panel of 15 EMU Member States. Empirical results indicate a significant difference between micro and macro elasticities for up to one half of the consistent product groups considered, implying preferences across EMU countries are not perfectly aligned with non-discriminatory tariffs. I conclude that both the absolute and relative macro elasticities are informative and that heterogeneous preference patterns link to current trade imbalances. (author's abstract)
Series: Department of Economics Working Paper Series

Les limites physiques des circuits à base de silicium étant en passe d'être atteintes, de nouveaux moyens doivent être trouvés pour outrepasser la fin de la loi de Moore. Beaucoup d'applications peuvent tolérer des approximations dans leurs calculs à différents niveaux, sans dégrader la qualité de leur sortie, ou en la dégradant de manière acceptable. Cette thèse se concentre sur les architectures arithmétiques approximatives afin de saisir cette opportunité. Tout d'abord, une étude critique de l'état de l'art des additionneurs et multiplieurs approximatifs est présentée. Ensuite, un modèle de propagation d'erreur virgule-fixe mettant en œuvre la densité spectrale de puissance est proposée, suivi d'un modèle de propagation du taux d'erreur binaire positionnel des opérateurs approximatifs. Les opérateurs approximatifs sont ensuite utilisés pour la reproduction des effets de la VOS dans les opérateurs arithmétiques exacts. Grâce à notre outil de travail open-source ApxPerf et ses bibliothèques synthétisables C++ apx_fixed pour les opérateurs approximatifs et ct_float pour l'arithmétique flottante basse consommation, deux études consécutives sont proposées, basées sur des applications de traitement du signal complexes. Tout d'abord, les opérateurs approximatifs sont comparés à l'arithmétique virgule-fixe, et la supériorité de la virgule-fixe est soulignée. Enfin, la virgule fixe est comparée aux petits flottants dans des conditions équivalentes. En fonction des conditions applicatives, la virgule-flottante montre une compétitivité inattendue face à la virgule-fixe. Les résultats et discussions de cette thèse donnent un regard nouveau sur l'arithmétique approximative et suggère de nouvelles directions pour le futur des architectures efficaces en énergie
The physical limits being reached in silicon-based computing, new ways have to be found to overcome the predicted end of Moore's law. Many applications can tolerate approximations in their computations at several levels without degrading the quality of their output, or degrading it in an acceptable way. This thesis focuses on approximate arithmetic architectures to seize this opportunity. Firstly, a critical study of state-of-the-art approximate adders and multipliers is presented. Then, a model for fixed-point error propagation leveraging power spectral density is proposed, followed by a model for bitwise-error rate propagation of approximate operators. Approximate operators are then used for the reproduction of voltage over-scaling effects in exact arithmetic operators. Leveraging our open-source framework ApxPerf and its synthesizable template-based C++ libraries apx_fixed for approximate operators, and ct_float for low-power floating-point arithmetic, two consecutive studies are proposed leveraging complex signal processing applications. Firstly, approximate operators are compared to fixed-point arithmetic, and the superiority of fixed-point is highlighted. Secondly, fixed-point is compared to small-width floating-point in equivalent conditions. Depending on the applicative conditions, floating-point shows an unexpected competitiveness compared to fixed-point. The results and discussions of this thesis give a fresh look on approximate arithmetic and suggest new directions for the future of energy-efficient architectures

Sustainable and equitable fisheries are central for addressing the challenges of the UN Sustainable Development Goal 14: Life Below Water. International trade, once presented by Walrasian economists as a panacea for fisheries development, has not markedly decreased poverty and has been related to the overexploitation of marine species. In this light the consequences of a continued expansion of seafood trade are highly uncertain and problematic. Two competing theoretical hypotheses predict either overexploitation or recovery of marine species when connected to international trade, respectively. The empirical literature finds trade relationships and connections of local fisheries to a large-volume market critical factors for social-ecological outcomes. Here, I combine these insights to show that multi-level links, between fishers & different markets (market manuscript) and marine species & trade relationships (squid manuscript), are critical to explain diverging social-ecological outcomes. In the market manuscript we model the transition from local, to multi-level (both local and global), to global markets in a two species fishery. We find this transition is non-linear, leading to fluctuations in species abundance as a result of abrupt switches between target species. Critical fluctuations of species abundance driven by new market connections are a result of large shifts in prices for one species and high asymmetries in expected income between the two species. The squid manuscript provides empirical and modeling evidence that cyclical changes in the ocean can drive social-ecological systems outcomes through changing interactions at multiple levels. The interactions between squid population and fishers and squid distribution and trading structures determines benefit distributions in the fishery. The lack of consideration of multi-level interactions related to trade in models for fisheries management is likely associated with a lack of processes for integrating the empirical and theoretical insights of two disciplines at the core of fisheries science. Social-ecological system scholars study more often empirical and fishery economics the theoretical aspects of interactions between trade and fisheries. One process suggested in this thesis to bridge insights from both disciplines in fishery models is the careful study of the important interactions in the empirical case. Comparison of these interactions with observed empirical interactions in other systems informs the model conceptualization that is then embedded in a theoretical framework. This leads to the development of models of intermediate complexity  that integrate insights on regular structures and patterns observed in real social-ecological systems. The squid manuscript exemplifies this integration. We integrate observed multi-level links in a standard fishery model between the squid population fishers and traders, and thus better represent the empirical system.  A continuous dialogue between empirics and theorycan help build models of intermediate complexity. To capture the complex elements of these social-ecological systems, in this young field of study, next to a continuous dialogue priority observed empirical dynamics can help question theoretical assumptions. This study seeks to contribute to the development of fisheries management models more suitable to face contemporary challenges of fisheries management by focusing on how multi-level interactions between fisheries and trade shape sustainable and equitable outcomes.

Duke and Jenkins defined a family of linear maps from spaces of weakly holomorphic modular forms of negative integral weight and level 1 into spaces of weakly holomorphic modular forms of half integral weight and level 4 and showed that these lifts preserve the integrality of Fourier coefficients. We show that the generalization of these lifts to modular forms of genus 0 odd prime level also preserves the integrality of Fourier coefficients.

In line with the canonical Heckscher-Ohlin model, trade liberalization instigates a pro-cess during which production of goods and services moves where it can be conducted in the most efficient way. Naturally, this process also entails changes in the labour demand of domes-tic industries. The most prominent example for this is the decline in employment in manufactur-ing industries due to increasing import competition from China. While the impact of this “China-Shock” on manufacturing employment in developed economies is widely acknowl-edged, research on how imports and exports interact to affect manufacturing and other indus-tries is scarce. For a panel of eleven Western European and Scandinavian countries, this thesis analysed how the occurrence of imports and exports has influenced labour demands in six in-dustries (both service and manufacturing) from 1996 to 2011 using data from Eurostat and the OECD. In general, the findings show that imports do put domestic industry-level labour demand in distress, especially in manufacturing industries. On the other hand, the findings also show that exports help to increase labour demand, especially in high-skill service industries.

Suitable sample preparation methods for the selected trace element analysis of a variety of foods were determined and the limitations of these methods were defined. Three day dietary surveys were completed for a number of groups in the community considered more likely to be at risk of trace element deficiency. The dietary copper, zinc and iron intakes of these groups were determined. A preliminary investigation into the chromium content of food was also completed. The nutritional significance of these findings is discussed.

 

 

 

 

 

Abstract

C-Level Paper in Political Science, by David Olsson, Autumn 2008. Supervisor: Malin Stegman McCallion. “Regime Type and Trade Policy: Has Increased Democratization Contributed to Lower Trade Barriers Among Autocratic States?”

 

In this paper a new two-level game theory, based on previous research and deductive reasoning, is constructed and tested empirically. The purpose is to examine if developing new democracies, trading with developing autocracies, is an explanatory factor of trade liberalization among the latter. The research questions are: 1) Have tariff rates in developing autocratic countries followed the pattern of reduced tariffs among their developing new democratic trading partners? And; 2) If this is the case, is there a relative shift in trade flows that confirms this change to be an effect of the new democracies’ presumed influence?

                      In order to sufficiently carry out an empirical scrutiny, seven other determinants found to have effects on trade policies in previous research, are accounted for using a “most similar systems design”. For reasons of delimitation, six autocracies and their fifteen most important trading partners, observed 1980-1999, have been paired and analyzed. Each pair consists of one autocracy that trades with new democracies and one that does not; regarding the other determinants they are as similar as possible. The used material is the World Development Indicators, the Polity IV Dataset, the Yearbook of International Trade Statistics, the World Economic Outlook Database, the Database of Political Institutions, statistics from the World Trade Organization, the Dataset of Armed Conflicts, and the Unweighted Average Tariffs Measurement.   

                      The conclusion is that there are no indicators that affirm the theory and research questions. However, the theory is not unambiguously falsified. Hence, studies on more countries and time spans are needed.       

 

 

 

 

 

Thesis (M.S.)--West Virginia University, 2004.
Title from document title page. Document formatted into pages; contains vii, 35 p. Vita. Includes abstract. Includes bibliographical references (p. 21).

This thesis attempts to establish the key factors influencing trade performance at both industry and enterprise-level. The underlying purpose is to consolidate the diverse literature in International Marketing as well as provide new insights. For the industry-level study, trade performance models are developed and tested to explain changes in exports and imports for a cross-section of New Zealand manufacturing industries between 1985 and 1990. Increased exports are associated with larger firm sizes, lower levels of advertising intensity and least trade protection (by either tariff or export subsidy). The largest increases in imports have been in those industries which are relatively highly concentrated, with higher R&D intensities, and higher levels of tariff protection and foreign ownership. The key to raising the export performance of manufacturing in general, seems to lie with increasing the quantity and improving the quality of product-related R&D carried out in New Zealand. A meta-analysis of 111 studies on export performance conducted during the period 1978-1991 was done to identify the key variables at enterprise-level. A multi-case study of 12 small to medium-sized firms, six from the timber processing industry and six from the electrical industrial machinery industry, was conducted to gather data for this section. The key variables identified in the meta-analysis are confirmed. The findings show that firm size drives export growth at both industry and enterprise-level. The study provides new insights on how the export behaviour process operates. Enterprises in both industries behave in a similar manner but there are significant differences in the behaviour between exporters and non-exporters. There is considerable overlap within export strategies among the group of eight exporters thus ruling out export strategy as an explanation for export performance.

As unmanned vehicle capabilities have matured, the design and development of autonomous collaborative Systems-of-Systems (SoS) has gained increased attention. This has been motivated by the indication that significant improvements in overall effectiveness may be possible by employing many systems in cooperation with one another. However, as the potential combinations of vehicles, subsystems, and operational concepts becomes increasingly large, a systematic approach is needed for designing and analyzing alternatives. Furthermore, the discrete nature of the problem can cause variations in effectiveness that are counter-intuitive, such as a point of diminishing returns as the number of systems grows. Systems-of-systems are hierarchical in nature, consisting of top-level mission requirements that are decomposed into system- and subsystem-level performance measures. The overarching research objectives of this dissertation are to show that the analysis of alternatives should be performed at varying levels of the SoS hierarchy and to provide novel means for performing those analyses. In particular, it has been postulated that a formulation built on an energy-based approach to multi-level analysis of SoS components will enable more accurate and transparent subsystem and system trade-offs. Various steps of the design process are established and argued for or against, and significant focus is placed on the analysis of alternatives. The foundation of the new method is laid on structured SoS engineering principles. The full substance comes together by incorporating unique aspects developed within this dissertation. A new virtual experimentation approach is presented for creating sensor performance representations that are functions of vehicle operations. The sonar equation is used as a baseline sensor model for comparison against the new virtual experimentation method. Dozens of forward-looking and side-scan sonar experiments are designed, and data is provided to show the extent to which typical sensor modeling over-predicts performance without vehicle operations considered. In addition, comparisons are made between possible representations of vehicle performance. An underwater vehicle sizing and synthesis process is developed to enable comparisons between system-level component modeling approaches. The experiments attest to significant gaps in accuracy when performing sensor and operational trade-offs without energy-based modeling of the collaborative vehicles. Finally, a heuristic path-planning algorithm is formulated, and mixed-integer linear programming is used to choose between alternative SoS designs. The developed method is demonstrated through a representative example problem: a group of unmanned underwater vehicles (UUVs) operating in a collaborative fashion to search for underwater objects. The example scenario provides an application for illustrating the phenomenon discussed in regards to the analysis of alternatives of collaborative SoS. The significance of providing more or less analytic detail is traced and the effect on mission requirements is quantified. Counter-intuitive results are highlighted, such as the observation that the increased energy required for systems to effectively collaborate can often out-weigh the benefits gained in overall mission effectiveness.