Tesis sobre el tema "Trace level"
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Cloke, M. "Trace element concentrations during coal liquefaction". Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378771.
Texto completoWeston, Daniel John. "Membrane inlet mass spectrometry for trace level analysis". Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310922.
Texto completoEdwards, David M. "Metal speciation at the trace level by derivative spectroscopy". Thesis, Manchester Metropolitan University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328240.
Texto completoByrne, Heather Elizabeth. "Adsorption, photocatalysis, and photochemistry of trace level aqueous mercury". [Gainesville, Fla.] : University of Florida, 2009.
Buscar texto completoZhao, Song. "HTTP Traffic Analysis based on a Lossy Packet-level Trace". Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1373030307.
Texto completoKume, Shinichi. "EFFECT OF DIETARY TRACE ELEMENT LEVEL AND HOT ENVIRONMENTAL TEMPERATURE ON TRACE ELEMENT NUTRITION OF HOLSTEIN DAIRY CATTLE". Kyoto University, 1987. http://hdl.handle.net/2433/78184.
Texto completoSotter, Solano Edgar Alexander. "Development of a thick film gas sensor for oxigen detection at trace level". Doctoral thesis, Universitat Rovira i Virgili, 2006. http://hdl.handle.net/10803/8471.
Texto completoEn 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.
Fuku, Xolile Godfrey. "Cytochrome C biosensor for the determination of trace level arsenic and cyanide compounds". Thesis, University of the Western Cape, 2011. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_4183_1319807269.
Texto completoAllen, Matthew Robert. "Thermal desorption techniques for the analysis of trace level VOC's in landfill gas". Thesis, Nottingham Trent University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285725.
Texto completoBoonjob, Warunya. "Automated sample preparation methods for the determination of trace level concentrations of environmental pollutants". Doctoral thesis, Universitat de les Illes Balears, 2012. http://hdl.handle.net/10803/84096.
Texto completoAutomatic 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.
Muaksang, Kittiya Chemistry Faculty of Science UNSW. "Development of reference methods and reference materials for trace level antibiotic residues in food using IDMS". Awarded by:University of New South Wales. Chemistry, 2009. http://handle.unsw.edu.au/1959.4/43262.
Texto completoSorensen, Ira Joseph. "Design and analysis of radiometric instruments using high-level numerical models and genetic algorithms". Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/29955.
Texto completoPh. D.
Li, Lihong. "Effects of Source and Level of Trace Minerals on Performance, Mineral Excretion, Intestine and Bone Development, and Immune Response in Commercial Turkeys". Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/37363.
Texto completoPh. D.
Alsubaie, MONA. "Measurements of the Trace Level of Radioactivity in Materials for Use in the SNO+ and nEXO Experiments at SNO Lab". Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38236.
Texto completoMcDonald, Shannon Scott. "Characterization and optimization of a high surface area-solid phase microextraction sampler for the collection of trace level volatile organic compounds in the field /". Download the thesis in PDF, 2006. http://www.lrc.usuhs.mil/dissertations/pdf/McDonald2006.pdf.
Texto completoAustin, P. J. E. "Palaeoconductivity, lake level fluctuations and trace element history of the Aral Sea since 400 AD : assessing the impact of natural climatic variability and anthropogenic activity". Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1446039/.
Texto completoMolina, Clemente Carlos. "Microarchitectural Techniques to Exploit Repetitive Computations and Values". Doctoral thesis, Universitat Politècnica de Catalunya, 2005. http://hdl.handle.net/10803/5988.
Texto completoAdemás, 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.
Cenanovic, Mirza. "Finite element methods for surface problems". Doctoral thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Produktutveckling, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-35369.
Texto completoLawgali, Youssef F. "Trace element levels in Mediterranean grains". Thesis, University of Aberdeen, 2010. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=136842.
Texto completoHarrington, Jane. "Women's local level trade union participation". Thesis, University of the West of England, Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327308.
Texto completoFleming, Y. H. "The H1 first level fast track trigger". Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416637.
Texto completoKgapola, Leslie Seth. "Trade unions service level and member satisfaction". Thesis, University of Pretoria, 2017. http://hdl.handle.net/2263/62678.
Texto completoThesis (PhD)--University of Pretoria, 2017.
Human Resource Management
PhD
Unrestricted
Dick, A. L. "Trace elements in Antarctic snow and air". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376538.
Texto completoGiri, Jeeten Krishna. "REGIONAL WAGE DIFFERENTIALS, INTRA-NATIONAL TRADE, AND INDUSTRY-LEVEL INTERNATIONAL TRADE, IN INDIA". OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1590.
Texto completoPierce, Justin Ronald. "Trade policy and performance plant-level evidence from manufacturers /". Connect to Electronic Thesis (CONTENTdm), 2009. http://worldcat.org/oclc/454152779/viewonline.
Texto completoWilliams, Clay G. "Free trade area of the Americas a three level analysis". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Mar%5FWilliams.pdf.
Texto completoThesis Advisor(s): Harold Trinkunas. "March 2006." Includes bibliographical references (p. 63-71). Also available online.
Ali, Haider Farhan. "Architecture Level Power-Performance Trade-ofts in Data-dominated Designs". Thesis, University of Southampton, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485441.
Texto completoSeo, Ok-Sun. "Pricing to market when exchange rate changes and output level matters". Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4371.
Texto completoThe 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.
Joda, Baker A. "Trace element levels of human fluids and tissues for Iraqi individuals". Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566842.
Texto completoDougherty, Sean. "Regulation and trade in development : explaining productivity at the firm level". Phd thesis, Université Panthéon-Sorbonne - Paris I, 2013. http://tel.archives-ouvertes.fr/tel-00984292.
Texto completoDaheshpour, Kasra. "Network level decision support system to assess railway track maintenance needs". Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8164/.
Texto completoDougherty, Sean Michael. "Regulation and trade in development : explaining productivity at the firm level". Thesis, Paris 1, 2013. http://www.theses.fr/2013PA010012/document.
Texto completoInstitutions, 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
Kaya, Murat. "Determination Of Germanium At Trace Levels By Chloride Generation Atomic Absorption Spectrometry". Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605147/index.pdf.
Texto completoC 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.
Limbert, Eduardo de castro Sobral Blanco. "Bioremediation of a model complex mixture of organic contaminants at trace levels". Thesis, University of York, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241044.
Texto completoAspalter, Lisa. "Estimating Industry-level Armington Elasticities For EMU Countries". WU Vienna University of Economics and Business, 2016. http://epub.wu.ac.at/4838/1/wp217.pdf.
Texto completoSeries: Department of Economics Working Paper Series
Kelle, Markus [Verfasser]. "Trade and FDI in Services: Firm Level Evidence for Germany / Markus Kelle". Kiel : Universitätsbibliothek Kiel, 2011. http://d-nb.info/1020201983/34.
Texto completoBarrois, Benjamin. "Methods to evaluate accuracy-energy trade-off in operator-level approximate computing". Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S097/document.
Texto completoThe 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
Elsler, Laura G. "Multi-level Interactions between Fisheries and Trade : Modeling intertwined social-ecological systems". Licentiate thesis, Stockholms universitet, Stockholm Resilience Centre, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-159470.
Texto completoLi, Han. "Modeling Gentrification on Census Tract Level in Chicago from 1990 to 2000". University of Toledo / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1336064031.
Texto completoGreen, Nathan Eric. "Integral Traces of Weak Maass Forms of Genus Zero Odd Prime Level". BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4161.
Texto completoKuhl, Hannes. "Trade-Labour-Dynamics : An industry-level analysis of the impact of trade on the adjustment of domestic labour demands". Thesis, Umeå universitet, Nationalekonomi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-137230.
Texto completoVan, Loon Gabriel. "Levels of trace metal contamination in selected stormwater BMPS and potential ecotoxic impacts". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0022/MQ31264.pdf.
Texto completoFlesher, Mary Melissa. "Acetylcholine levels in the prefrontal cortex and hippocampus during trace and delay conditioning". CSUSB ScholarWorks, 2008. https://scholarworks.lib.csusb.edu/etd-project/3370.
Texto completoRoesch, Karen. "The nutritional significance and levels of certain trace elements in selected Australian diets". Thesis, Queensland University of Technology, 1987. https://eprints.qut.edu.au/36736/1/36736_Roesch_1987.pdf.
Texto completoOlsson, David. "Regime Type and Trade Policy : Has Increased Democratization Contributed to Lower Trade Barriers Among Autocratic States?" Thesis, Karlstad University, Faculty of Social and Life Sciences, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-3407.
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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.
Driscole, Robert E. "Employment opportunities and skills necessary for entry-level employment in the timber industry". Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3304.
Texto completoTitle from document title page. Document formatted into pages; contains vii, 35 p. Vita. Includes abstract. Includes bibliographical references (p. 21).
Kleinwechter, Ulrich [Verfasser] y Harald [Akademischer Betreuer] Grethe. "Village level impacts of trade reform in China / Ulrich Kleinwechter. Betreuer: Harald Grethe". Hohenheim : Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim, 2011. http://d-nb.info/1027524524/34.
Texto completoChetty, Kamala (Sylvie). "International trade performance of New Zealand manufacturing: An industry and enterprise-level study". Thesis, University of Canterbury. Management, 1993. http://hdl.handle.net/10092/4321.
Texto completoMolino, Nicholas Anthony. "A multi-level trade-off methodology for analyzing collaborative system-of-system alternatives". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53585.
Texto completoMilushev, Nikola. "Trade relations and the level of integration between Bulgaria and the European Union". Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272114.
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