La toxicitat del mercuri depèn de la seva probabilitat d'exposició, factors geoquímics i ecològics, i en particular de l'espècie química en què es troba. No obstant això, el nombre i veracitat de tècniques analítiques d'especiació segueix sent molt limitat. En conseqüència, les tècniques espectroscòpiques d'absorció de raig-X (XAS) basades amb la radiació sincrotró, han esdevingut eines interessants i fàcilment disponibles per a superar la manca existent en aquest camp. Entre altres, les tècniques més comuns són XANES (X-ray Absorption Near Edge Spectroscopy) i EXAFS (Extended X-ray Absorption Fine Structure). Altres progressos en aquest camp es basen en la unió de les tècniques d'absorció amb a una alta resolució espacial a nivell de microescala, usant les tècniques µ-XRF (microscopic X-ray Fluorescence) o µ-XAS. La comprensió del perill per al medi ambient plantejat pel metilmercuri (CH3HgCl i CH3HgOH) adsorbit sobre típics components del sòl ha estat assolida per la combinació de les tècniques XAS i bacteris sensors luminiscents (Escherichia coli MC1061, pmerBRBSluc). La quantitat de Hg adsorbit ha resultat ser depenent del pH, mentre que el caràcter de l'enllaç independent del pH. En comparar la interacció entre el metilmercuri i les argiles o materials húmics, els primers han donat lloc a un caràcter iònic més alt i per tant a una possibilitat de mobilització del mercuri més gran. A més, aquesta interacció ha resultat ser més estable pel CH3HgOH que pel CH3HgCl.El districte d'Almadén a Ciudad Real ha donat lloc a un dels ambient més impactats pel Hg arreu del món. En aquest context, les tècniques XAS (juntament amb SES, XRD i SEM-EDS) s'han utilitzat per a estudiar el comportament del mercuri en aquesta regió. El cinabri s'ha trobat que és l'espècie principal en minerals i sòls, mentre que el metacinabri és l'espècie principal en les escòries. En totes les mostres, també s'han trobat sals més solubles de mercuri (HgCl2, HgSO4 i schuetteite). Les tècniques de microsonda també han revelat correlacions elementals entre el Hg i el Pb, Ni i S, indicant un possible acoblament geoquímic d'aquests elements. Les correlacions també s'han identificat entre el Hg i Fe/Mn, el qual s'ha atribuït a l'absorció del mercuri sobre els oxihidròxids de Fe i Mn. D'altra banda, les indústries clor-àlcali amb càtode de mercuri han estat un dels usos industrials més importants del mercuri a Europa occidental. El gravamen del comportament del mercuri en aquests ambients ha estat conduït per les tècniques XAS acoblades a SES. La informació d'especiació ha demostrat que els compostos inorgànics de mercuri dominen en totes les mostres de sòl considerades, sent cinabri i corderoite les principals espècies. No obstant això, també s'han identificat fases lleument solubles (HgO i HgSO4) en proporcions de menor importància. Per altra banda, l'anàlisi de µ-XRF ha demostrat una correlació geoquímica de Hg, Cu i Ni, que suggereixen la formació de possibles solucions sòlides d'aquests elements dintre de la mateixa estructura cristal·lina. Finalment, les tècniques de microsonda amb radiació sincrotró s'han proposat per a l'observació directa del mercuri i altres elements presents en dents humanes restaurades amb amalgames de mercuri. Les anàlisis han demostrat una difusió mínima del Hg a través de la dent, amb la identificació d'una correlació lineal entre el Hg i el Cu. Per altra banda, s'ha identificat una difusió significativa del Cu i el Zn de l'amalgama a la regió de la dentina, suggerint un possible intercanvi del Ca2+ amb el Cu2+/Zn2+ en els cristalls d'hidroxiapatita (Ca10(PO4)6(OH)2). Per altra banda, µ-EXAFS ha determinat que l'ambient molecular inicial del Hg en la regió de l'amalgama està limitat per la fase ?-Ag2Hg3 formada durant el procés d'amalgamació / Toxicity of mercury is determined by the likelihood of exposure, geochemical and ecological factors, and in particular by the chemical species in which it is found. Chemical speciation become of an utmost importance when assessing the risk associated to mercury impacted environments. Despite this, the number and reliability of analytical techniques able to recognise different mercury species is still very limited, even more when dealing with solid samples. Hence, synchrotron-based x-ray absorption spectroscopic (XAS) techniques have risen as an interesting and readily available tool to overcome the existing speciation gap. Among others, the most common techniques dealing with speciation are XANES (X-ray Absorption Near Edge Spectroscopy) and EXAFS (Extended X-ray Absorption Fine Structure). Further developments in this field focus on the coupling of x-ray absorption techniques to a spatial resolution at a micro-scale level, by using µ-XRF (microscopic X-ray Fluorescence) or µ-XAS techniques.The understanding of the environmental hazard posed by methylmercury (CH3HgCl and CH3HgOH) adsorbed onto a number of key soil materials has been accomplished by the combination of XAS techniques and luminisent sensor bacteria (Escherichia coli MC1061, pmerBRBSluc). The amount of Hg adsorbed was observed to be pH-dependent, whereas the bond character was found to be pH-independent. When comparing interaction between methylmercury and clays or humic materials, the former resulted in a higher ionic character and consequently in a larger possibility of mercury mobilisation. Additionally, this interaction was observed to be more stable for CH3HgOH than for CH3HgCl, due to the higher reactivity of the hydroxyl group. The Almadén district in Ciudad Real has lead to one of the most Hg-impacted environments found around the world. In this context, XAS techniques (complemented with SES, XRD and SEM-EDS analyses) have been utilised to study the mercury behaviour in this region. Cinnabar has been found to be the main species in ores and soils, whereas metacinnabar was the main species in slag. In all samples, slightly soluble mercury salts (HgCl2, HgSO4 and schuetteite) have been also found. Microprobe techniques have also revealed elemental correlations between Hg and Pb, Ni and S, indicating a possible geochemical linkage of these elements. Correlations were also identified between Hg and Fe/Mn, which have been attributed to sorption of mercury onto oxy-hydroxides of Fe and Mn. Chlor-alkali industries with mercury cathode remain as one of the most important industrial applications of mercury in Western Europe, which become one of the most important point-sources for mercury contamination. The assessment of mercury behaviour in these environments has been conducted by XAS techniques coupled to SES. Speciation information showed that inorganic mercury compounds dominate in all soil samples considered, being cinnabar and corderoite the main species. However, slightly soluble phases (HgO and HgSO4) have been also identified in minor proportions. On the other hand, µ-XRF analysis has shown a geochemical correlation of Hg, Cu and Ni, which suggest the possible formation of solid solutions of these elements within the same crystalline structure.Finally, synchrotron X-ray microprobe techniques have been proposed for the direct observation of mercury and other elements present in human teeth restored with dental amalgams. Microprobe analyses showed a minimum diffusion of Hg throughout the tooth, with the identification of a linear correlation between Hg and Cu. On the other hand, a significant diffusion of Cu and Zn from the amalgam to the dentine region was identified, which suggested the possible exchange of Ca2+ by Cu2+/Zn2+ in hydroxiapatite crystals (Ca10(PO4)6(OH)2). On the other hand, µ-EXAFS has determined that the initial molecular environment of Hg in the amalgam region is limited to the ?-Ag2Hg3 phase formed during the amalgamation process.

No description available.

Dual energy imaging has made it possible to enhance contrast in medical images using images containing different energy information, by combining low and high energy images. Dual energy data can either be acquired using double exposures or splitting the energy spectrum into two images using one exposure. This thesis presents investigations of dual energy imaging using a detector solution developed by XCounter which provides dual energy images in a single exposure with a threshold separating low and high energy images. Phantom experiments with phantoms of aluminum and plexiglas were performed using weighted logarithmic subtraction and basis material decomposition to produce dual energy images. Methods were validated and images were evaluated in terms of signal difference in noise ratio to find the threshold and tube voltage combination for optimum energy spectrum separation. The methods were also tested on biological materials using bone, soft tissue and iodine solution as contrast enhancer, to investigate K-edge imaging.  Optimal separation of plexiglas and aluminum were found at 70 kVp and the threshold parameter set within a range of 8 to 9, which corresponds to approximately 30 to 34 keV. For K-edge imaging, the optimum separation were found close to K-edge energy of iodine. The results found in the phantom study correlated with results from the biological material study.

The main subject of this thesis is the study of electronic and magnetic properties of materials containing 3d transition metal atoms. Our motivation stems mainly from the modern fields of spintronic computing and solar energy conversion. The two primary goals of this work are to determine (i) why certain transition metal impurities in certain semiconductors can induce magnetic properties suitable for spintronic computing applications, and (ii) how transition metal impurities can be used to modify the electronic band gaps of semiconductors and insulators in ways useful for harnessing solar energy and for other applications. To accomplish these goals, we have applied both experimental and theoretical tools. We studied high quality materials prepared by advanced synthesis techniques using x-ray spectroscopy methods at synchrotron light sources. The results of these experiments were interpreted using a variety of theoretical techniques, primarily using computational software developed as part of this thesis and discussed herein. Regarding the study of introducing transition metal impurities into semiconductors to induce magnetic properties, we first developed and demonstrated a method to determine the location of impurity atoms within the host semiconductor lattice. This allowed to us explain the presence and absence of ferromagnetism in samples prepared under only slightly different synthesis conditions, which helped to address some long--standing issues in the spintronics field. We then studied an advanced and promising material -- indium (III) oxide with iron impurities -- to determine how magnetic ordering was maintained up to room temperatures. Our techniques unveiled that a portion of the iron atoms were coupled to oxygen vacancies in the material to create conditions which propelled the observed magnetism. This finding confirmed some earlier theoretical predictions by others in the field. For the study of electronic band gap modifications in semiconductors and insulators via the incorporation of transition metal atoms, we investigated a wide range of materials synthesized using different techniques. Again, we used experimental techniques to determine the location of impurity atoms within the materials, and used this to understand how band gaps were modified upon the introduction of the impurities. For Ti implantation into SiO2, Ni substitution into ZnO, and a new material, MnNCN, we have determined the electronic band gaps and used our techniques to explain how the values for the gaps arise. Finally, an additional outcome of this thesis work is a software program capable of simulating x-ray spectra using various advanced quantum models. We rewrote and built upon powerful existing programs and applied the result to the above studies. Our software was further applied in a collaborative effort with other researchers at the Canadian Light Source to study the differences in two experimental techniques for measuring x-ray absorption: partial and inverse partial fluorescence yields. By using the proper absorption and scattering formalisms to simulate each technique, we were able to explain the differences between the experimental spectra obtained from each. We explain fluorescence yield deviations using an analysis based on the spin configuration of different states, suggesting that the technique can be further extended as a quantitative spin state probe. These results could have significant implications for the field of soft x-ray absorption spectroscopy.

Las mol eculas metal-org anicas en la intercara con sustratos met alicos son sistemas interesantes para aplicaciones futuras en la grabaci on magn etica y dispositivos de espintr onica, ya que prometen sustituir algunos de los com- ponentes magn eticos basados en metales en uso hoy en d a. Las mol eculas que llevan esp n son materiales muy atractivos, tanto como capas nas bi- dimensionales en estructuras de multi-capas o como unidades magn eticas individuales, debido a sus reducidas dimensiones y propiedades funcionales. Entre esta clase de mol eculas, los imanes moleculares (SMMs) son los m as prometedores, ya que combinan propiedades magn eticas de bulk y dimensio- nes a escala molecular. Varios problemas limitan su aplicaci on en dispositivos reales: la principal es la baja temperatura de bloqueo TB, t picamente alrede- dor de la temperatura de liquefacci on de helio, por debajo del cu al los SMMs se comportan como nanoimanes; adem as, controlar el momento magn etico de una sola mol ecula no es una tarea f acil. Para superar estos obst aculos se est an investigando muchas estrategias y la m as prometedora parece ser la deposici on sobre sustratos magn eticos. Para el estudio de estos materiales, las espectroscop as de radiaci on sin- crotr on representan t ecnicas muy poderosas: la espectroscop a de absorci on de rayos X (XAS) y el dicro smo magn etico circular de rayos X (XMCD), en particular, permiten medir selectivamente diferentes elementos y medi- ciones independientes de los momentos at omicos orbitales y de esp n, can- tidades fundamentales para la comprensi on de las propiedades magn eticas macrosc opicas de la materia. En este estudio se ha investigado la interacci on del SMM TbPc2 con su- per cies ferromagn eticas (FM) de Ni. Usando la magnetometr a XMCD, se ha demostrado que TbPc2 se acopla antiferromagneticamente a la capa de Ni a trav es de la interacci on de supercanje mediada por el ligando. La ma- gnitud, pero no el signo, de la energ a de acoplamiento de canje puede ser ajustado mediante la reducci on o la oxidaci on del sustrato. Contrariamente a las mol eculas paramagn eticas, encontramos que el momento magn etico de los SMMs no sigue la magnetizaci on de la capa FM subyacente en cualquier con- dici on, sino que depende de la orientaci on relativa de los ejes de anisotrop a magn etica de la mol ecula y del sustrato, de la interacci on de supercanje y de la interacci on Zeeman. Las mol eculas de TbPc2, acopladas al Ni, conser- van sus propiedades intr nsecas de SMM, pero tambi en presentan una mejor estabilidad t ermica respecto a la mol ecula aislada, lo que demuestra una estrategia efectiva para incluir SMM en dispositivos de espintr onica. Se puede dar un paso m as hacia el control de un SMM estudiando el acoplamiento con sustratos antiferromagn eticos (AFM). Esto permitir a la inversi on de la magnetizaci on de capas moleculares con respecto al sustrato que bloquea el esp n. El fen omeno clave para demostrar este acoplamiento es el exchange bias, la anisotrop a magn etica unidireccional en la intercara entre capas FM y AFM, usada en espintr onica para estabilizar y controlar la magnetizaci on de estructuras multicapas. Aqu se investiga la posibilidad de inducir exchange bias entre SMM y capas AFM met alicas o de oxido. Las medidas de XMCD muestran que las mol eculas de TbPc2 depositadas sobre una capa na AFM de Mn tienen, despu es del enfriamiento con un campo magnetico externo aplicado, una curva de magnetizaci on abierta y despla- zada horizontalmente. Esta evidencia de exchange bias es coherente con la observaci on de esp nes bloqueados en la capa de Mn que se acoplan paralela- mente al momento magn etico del Tb, durante el enfriamiento en campo. Al contrario, las mol eculas depositadas sobre sustratos de CoO presentan ciclos de magnetizaci on paramagn eticos sin indicaci on alguna de exchange bias. Estos experimentos demuestran la capacidad de los SMMs para polarizar los esp nes bloqueados no compensados de un antiferromagneto y para formar heteroestructuras metal-org anicas que presentan exchange bias. Por ultimo, se ha puesto atenci on en la mol ecula paramagn etica MnPc. Se ha depositado esta mol ecula en varios sustratos, tanto magn eticos como no magn eticos, y se ha llevado a cabo un estudio sistem atico de la modi- caci on de la con guraci on electr onica en las diferentes muestras. Lo que observamos es que la con guraci on electr onica del MnPc se ve muy afecta- da por el sustrato y que el mecanismo principal que induce los cambios es probablemente la transferencia de carga. El MnPc en sustratos FM de Ni se comporta previsiblemente como las otras mol eculas paramagn eticas en capas FM, siguiendo la magnetizaci on del sustrato, mientras que, en capas AFM de oxido, no se observa exchange bias, como en el caso de SMM TbPc2. Tambi en hemos tratado de calcular el momento magn etico de cada muestra, descubriendo resultados inesperados que necesitan ser aclarados. Este estu- dio se encuentra todav a en una primera etapa, y necesita el apoyo de otras mediciones y c alculos teoric os para con rmar nuestras suposiciones. / Metal-organic molecules at the interface with metallic substrates are intere- sting systems for future applications in electronic and spintronic devices, as they hold promise for replacing some of the metal-based magnetic compo- nents in use today. Spin carrying molecules are highly attractive materials, both as ordered two-dimensional lms in multilayer structures and as single magnetic units, because of their reduced dimensions and functional proper- ties. Among this class of molecules, single molecule magnets (SMMs) are the most promising materials, because they combine bulk magnetic properties and molecular scale dimensions. Several problems limit their application in real devices; however the main one is the low blocking temperature (TB), tipically in the helium liquid range, under which SMMs behave like nanoma- gnets; furthermore, it is not an easy task to control the magnetic moment of a single molecule. To overcome these obstacles, many strategies are under investigation, including single molecules in break junctions, molecules depo- sition on magnetic substrates, change of the organic ligand to modify the ligand eld, etc.. To study these materials, synchrotron radiation spectroscopy represents a powerful technique: X-ray absorption spectroscopy (XAS) and x-ray magne- tic circular dichroism (XMCD), in particular, allow element selectivity and independent measurements of the atomic orbital and spin moments, funda- mentals quantities for understanding the macroscopic magnetic properties of the matter. We investigate the interaction of TbPc2 SMMs with ferromagnetic (FM) Ni surfaces. Using XMCD magnetometry, we show that TbPc2 couple anti- ferromagnetically to Ni lms through ligand-mediated superexchange. The magnitude, but not the sign of the exchange coupling energy, can be tailored by reducing or oxidizing the substrate. Contrary to paramagnetic molecules, we nd that the SMM magnetic moment does not follow the magnetization of the underlying FM layer, depending on the relative orientation of the mo- lecule and substrate magnetic anisotropy axes, superexchange, and Zeeman interaction. Coupled to Ni, TbPc2 retain their intrinsic SMM properties, but they exhibit enhanced thermal stability relative to isolated molecules, demonstrating an e ective approach to include SMM in spintronic devices. A further step towards the control of SMMs is to induce coupling with an antiferromagnetic (AFM) substrate. This nding may enable independent magnetization reversal of molecular layers with respect to the pinning sub- strate. The key phenomenon in this case is exchange bias, the unidirectional magnetic anisotropy at the interface between FM and AFM layers, used in spintronics to stabilize and control the magnetization of multilayer structures. Here we investigate the possibility to induce exchange bias between SMMs and metallic or oxide AFM layers. Element-resolved XMCD measure- ments show that TbPc2 molecules deposited on an AFM Mn thin lm present magnetic hysteresis and a negative horizontal shift of the Tb magnetization loop after eld cooling. This evidence of exchange bias is consistent with the observation of pinned spins in the Mn layer that couple parallel to the Tb magnetic moment during eld cooling. Conversely, molecules deposited on CoO substrates present paramagnetic magnetization loops with no indica- tion of exchange bias. These experiments demonstrate the ability of SMM to polarize the uncompensated pinned spins of an antiferromagnet and realize metal-organic exchange biased heterostructures. Finally, we draw attention to the behaviour of paramagnetic molecules, such as MnPc. We deposited MnPc on several substrates, both magnetic and non magnetic, and performed a systematic study of how the electronic con guration of the Mn ions and their magnetic moment are modi ed. What we observe is that the MnPc electronic con guration is highly a ected by the substrate and that the main mechanism inducing changes is likely charge transfer. MnPc on FM Ni behaves, as expected, like a normal paramagnetic molecule on FM layers, mimicking the substrate magnetization, while no exchange bias is observed on AFM oxides layers, as for TbPc2 SMM. We also tried to estimate the magnetic moment for each sample, nding unexpected results that need to be clari ed. This study is still at a rst stage, and needs the support of further measurements and calculations to con rm our assumptions.

Rapid progress over the last decade on large area thin film transistor (TFT) arrays led to the emergence of high-performance, low-power, low-cost active matrix flat panel imagers. Despite the shortcomings associated with the instability and low mobility of TFTs, the amorphous silicon TFT technology still remains the primary solution for the backplane of flat panel imagers. The use of a-Si:H TFTs as the building block of the large area integrated circuit becomes challenging particularly when the role of the TFT is extended from traditional switching applications to on-pixel signal amplifier for large area digital imaging. This is the idea behind active pixel sensor (APS) architectures in which under each pixel an amplifier circuit consisting of one or two switching TFTs integrated with one amplifying TFT is fabricated. To take advantage of the full potential of these amplifiers, it is crucial to develop APS architectures to compensate for the limitations of the TFTs. In this thesis several APS architectures are designed, simulated, fabricated, and tested addressing these challenges using the mask sets presented in Appendix A. The proposed APS architectures can compensate for inherent stabilities of the comprising TFTs. Therefore, the sensitivity of their output data to the transistor variations is significantly suppressed. This is achieved by using a well defined external current source instead of the traditional voltage source to reset the APS architectures during the reset cycle of their periodic operation. The performance of these circuits is analyzed in terms of their stability, settling time, noise, and temperature-dependence. For appropriate readout of the current mode APS architectures, high gain transresistance amplifiers with correlated double sampling capability is designed, simulated and fabricated in CMOS technology. Measurement and measurement based calculation results reveal that the proposed APS architectures can meet even the stringent requirements of low noise, real-time digital fluoroscopy.

In a time of global environmental problems due to overuse of fossil fuels, and a subsequent depletion of the supplies, hydrogen is considered as one of the most important renewable future fuels for use in clean energy systems with zero greenhouse-gas emission. Hydrogen storage is the main issue that needs to be solved before the technology can be implemented into key areas such as transport. The high energy density, good stability and reversibility of metal hydrides make them appealing as hydrogen storage materials. In this thesis research on synthesis and hydrogen absorption properties for intermetallic compounds based on scandium and aluminium is reported. The compounds were synthesized by arc melting or induction melting and exposed to hydrogen in a high pressure furnace. Desorption investigations were performed by thermal desorption spectroscopy. The samples were analyzed by x-ray powder diffraction and electron microscopy. ScAlNi, crystallizing in the MgZn2-type structure (space group: P63/mmc; a = 5.1434(1) Å, c = 8.1820(2) Å), was found to absorb hydrogen by two different mechanisms at different temperature regions. At ~120 °C hydrogen was absorbed by solid solution formation with estimated compositions up to ScAlNiH0.5. At ~500 °C hydrogen was absorbed by disproportionation of ScAlNi into ScH2 and AlNi. The reaction was found to be fully reversible due to destabilization effects which lowered the decomposition temperature of ScH2 by ~460 °C.

Dokumentärfotografiet befinner sig i ständig utveckling. I takt med att människan blir mer rörlig ökar även dess kontakt med andra kulturer. Den här rapporten undersöker hur människor med olika kulturell bakgrund uppfattar kulturella konnotationer i dokumentärfotografier. Området studien avser att studera är delstaten New Mexico i USA. Rapporten inleder med att definiera den dokumentärfotografiska utveckling av landskapet som skett i delstaten. Den fortsätter sedan med att gå in på att definiera en ny typ av dokumentärfotografi som praktiseras av fotografen Patrick Nagatani. Han använder sig av en metod som Joan Fontcuberta definierar som X-ray realism. Studien har genomförts genom att producera tre olika fotografier med hjälp av metoden X-ray realism för att sedan implementera kulturella och ideologiska anknytningar i dem. Studien låter sedan responsgrupper i både Sverige och USA analysera och motivera hur de förhåller sig till de kulturella referenserna och för att klargöra om Nagatanis sätt att fotografera på fungerar globalt eller om betraktaren måste vara bosatt på platsen för att förstå fotografiernas innebörd.

<p><i>Lactococcus lactis,</i> prolidase (<i>Lla</i>prol) hydrolyzes Xaa-Pro dipeptides. Since Xaa-Pro is known as bitter peptides, <i>Lla</i>prol is potentially applicable to reduce bitterness of fermented foods. <i>Lla</i>prol shows allosteric behaviour and substrate inhibition, which are not reported in other prolidases. Computer models of <i>Lla</i>prol based on an X-ray structure of non-allosteric <i>Pyrococcus furiosus</i> prolidase showed that a loop structure (Loop^32-43) is located at the interface of the protomers of this homodimeric metallodipeptidase. This study investigated roles of four charged residues (Asp³⁶, His³⁸, Glu³⁹, and Arg⁴⁰) of Loop^32-43 in <i>Lla</i>prol using a combination of kinetic examinations of ten mutant enzymes and their molecular models. Deletion of the loop structure by Î36-40 mutant resulted in a loss of activity, indicating Loop^32-43 is crucial for the activity of <i>Lla</i>prol. D36S and H38S exhibited 96.2 % and 10.3 % activity of WT, whereas little activities (less than 1.0 % of WT activity) were observed for mutants E39S, D36S/E39S, R40S, R40E, R40K and H38S/R40S. These results implied that Glu³⁹ and/or Arg⁴⁰ play critical role(s) in maintaining the catalytic activity of <i>Lla</i>prol. These observations suggested that the loop structure is flexible and this attribute, relying on charge-charge interactions contributed by Arg⁴⁰, Glu³⁹ and Lys¹⁰⁸, is important in maintaining the activity of <i>Lla</i>prol. When the loop takes a conformation close to the active site (closed state), Asp³⁶ and His³⁸ at the tip of the loop can be involved in the catalytic reaction of <i>Lla</i>prol. The two active mutant prolidases (D36S and H38S) resulted in modifications of the unique characteristics; the allosteric behaviour was not observed for D36S, and H38S <i>Lla</i>prol showed no substrate inhibition. D36E/R293K, maintaining the negative charge of position 36 and positive charge of position 293, still possessed the allosteric behaviour, whereas the loss of the charges at these positions (D36S of this study and R293S of a previous study (Zhang et al., 2009 BBA-Proteins Proteom 1794, 968-975) eliminated the allosteric behaviour. These results indicated the charge-charge attraction between Asp³⁶ and Arg²⁹³ is important for the allostery of <i>Lla</i>prol. In the presence of either zinc or manganese divalent cations as the metal catalytic centre, D36S and H38S enzymes also showed different substrate preferences from WT <i>Lla</i>prol, implying the influence of Asp³⁶ and His³⁸ on the substrate binding. D36S and H38S also showed higher activities at pH 5.0 to 6.0, in which range WT <i>Lla</i>prol steeply decreased its activity, indicating Asp³⁶ and His³⁸ are involved in the active centre and influence the microenvironment of catalytic His²⁹⁶. The above observations are attributed to modifications of their local structure in the active centre since the temperature dependency and thermal denaturing temperature indicated little effects on the overall structure of the <i>Lla</i>prol mutants.</p> <p>From these results, we concluded that the unique behaviours of <i>Lla</i>prol are correlated to Loop^32-43 and Asp³⁶ and His³⁸ on it. When Loop^32-43 takes a closed conformation, Asp³⁶ interacts with Arg²⁹³ via charge-charge attraction to form an allosteric subsite. The saturation of the allosteric site with substrates further allowed the communications of His³⁸ with S₁ site residues to complete the active site. When the substrate concentration becomes higher than it is required to saturated productive S₁' site, His³⁸, Phe¹⁹⁰ and Arg²⁹³ would resemble the residue arrangement of S₁' site residues (His²⁹², Tyr³²⁹, and Arg³³⁷) and bind to the proline residue of substrates. This non-productive binding would prevent the conformational change of Loop^32-43, which further results in the substrate inhibition. For further confirmation of this mechanism, crystallographic studies will be conducted. In this thesis, we have indentified the conditions to produce crystals of <i>Lla</i>prol proteins.</p>

Rapid progress over the last decade on large area thin film transistor (TFT) arrays led to the emergence of high-performance, low-power, low-cost active matrix flat panel imagers. Despite the shortcomings associated with the instability and low mobility of TFTs, the amorphous silicon TFT technology still remains the primary solution for the backplane of flat panel imagers. The use of a-Si:H TFTs as the building block of the large area integrated circuit becomes challenging particularly when the role of the TFT is extended from traditional switching applications to on-pixel signal amplifier for large area digital imaging. This is the idea behind active pixel sensor (APS) architectures in which under each pixel an amplifier circuit consisting of one or two switching TFTs integrated with one amplifying TFT is fabricated. To take advantage of the full potential of these amplifiers, it is crucial to develop APS architectures to compensate for the limitations of the TFTs. In this thesis several APS architectures are designed, simulated, fabricated, and tested addressing these challenges using the mask sets presented in Appendix A. The proposed APS architectures can compensate for inherent stabilities of the comprising TFTs. Therefore, the sensitivity of their output data to the transistor variations is significantly suppressed. This is achieved by using a well defined external current source instead of the traditional voltage source to reset the APS architectures during the reset cycle of their periodic operation. The performance of these circuits is analyzed in terms of their stability, settling time, noise, and temperature-dependence. For appropriate readout of the current mode APS architectures, high gain transresistance amplifiers with correlated double sampling capability is designed, simulated and fabricated in CMOS technology. Measurement and measurement based calculation results reveal that the proposed APS architectures can meet even the stringent requirements of low noise, real-time digital fluoroscopy.