Phosphor (P) ist ein für alles Leben notwendiges essentielles Nährelement. Die heutige globalisierte und intensivierte agrarische Produktion benötigt daher die Anwendung großer Mengen Phosphatgesteins, welches eine endliche Ressource darstellt. Gleichzeitig ist der intensive P Gebrauch mit der Eutrophierung von Gewässern verbunden. Es besteht daher Forschungsbedarf um die landwirtschaftliche Produktion zu erhalten. Ziel dieser Arbeit ist die in der Region Berlin-Brandenburg nach Ansatzpunkten für ein verbessertes P Management zu suchen. Hierfür wurde für 2011 eine Substanzflussanalyse (SFA) für P erstellt und Pflanzenproduktion der Jahre 2005-2012 genauer untersucht. Mit Hilfe einer Briefumfrage wurde Daten von 119 Bauernhöfen ausgewertet und mit dem pflanzenverfügbaren P Gehalt (PVP) der landwirtschaftlichen Nutzfläche abgeglichen (LNF). Im Ergebnis zeigt sich für die Region eine negative P Bilanz der LNF(-3.617 t P) und ein hohes Recyclingpotential in Abfall (933 t P) und Abwasser (3.921 t P). P in mineralischen Düngemitteln belief sich auf 4.447 t. Der Gesamtentzug über die Ernte ohne Stroh betrug 15.283 t P und war vergleichbar zu 2006, das Jahr des geringsten P-Entzugs. P-Entzug durch die Ernte schwankte um 7.069 t P/a von 2005 bis 2013, abhängig vom Ertrag der Hauptfeldfrüchte, welche durch die Wetter- und Bodenbedingungen bestimmt wurde. Hieraus ergeben sich mögliche Konsequenzen für P-Flüsse in Bezug auf den Klimawandel, die an den Wasserhaushalt und die Temperatur gekoppelt sind. Die Analyse der Umfrage ergab, dass die kleinen und mittgroßen Einzelunternehmen höhere PVP Werte in der LNF aufwiesen. Die größeren Unternehmensformen regierten empfindlich auf Faktoren, die niedrige PVP-Werte begünstigten. Pacht, Grünland, extensive Rinderhaltung, und viehlose ökologische Landwirtschaft waren mit niedrigen PVP-Werten assoziiert. Biogasanlagen und intensive Tierhaltung, zum Teil auch in Kombination miteinander standen im Zusammenhang mit hohen PVP-Werten. / Phosphorus (P) is an essential nutrient for all life on earth and it is thus needed in agricultural production. Today’s globalized and intensified agricultural production has led to the dependency on P inputs which are fed by phosphate rock, being a finite resource. In contrast, excessive P is a major driver in eutrophication. To sustain agricultural production, there is a need to address this problem. The aim of this thesis was to identify points at which P management could be improved for the region Berlin-Brandenburg. To analyze the system and screen for improvement, a substance flow analysis (SFA) for P for the year 2011 was compiled and for crop production the years 2005-2012 were analyzed. Also, data from 119 farms was obtained by a letter survey and relations between farm structural factors and soil test P (STP) were drawn. The results showed a negative balance for agricultural soils (-3,617 t P) and a considerable recycling potential in waste (933 t P) and wastewater (3,921 t P). Mineral fertilizer inputs amounted to 4,447 t P. P removal by crops was 15,283 t without straw and residues, being almost as low as in 2006; the year with the lowest removal by main crops. P removal by harvest varied significantly (7,069 t P/yr from 2005 to 2013) and depended on the performance of main crops which in turn is influenced by weather and soil. As a result of this, climate change may interact significantly with P flows in agriculture. Here, important variables are connected to conditions in P uptake and plant growth in general (e.g. water supply and temperature). The analyses of farms in the region showed that individual farms of small to medium size had more land with (very) high STP. Larger partnerships and companies/cooperatives were susceptible to factors causing low STP. Tenancy, grassland, extensive cattle and stockless organic farming had a lowering effect on STP. Biogas plants and intensive (cattle) farming, partly combined, were connected to a rise in STP.

Ziele dieser Dissertation sind die Aufklärung der Strömungsverhältnisse und Untersuchungen zum Verhalten von Arzneimittelrückständen im Tegeler See, die Entwicklung eines Simulationsmodells für Szenarioberechnungen sowie die Ableitung neuer Bewirtschaftungskonzepte unter Zuhilfenahme der gewonnenen Erkenntnisse und Modellergebnisse. Das zweidimensionale Strömungsmodell 2D-POM kann die Mischungsverhältnisse der beiden Zuflüsse zum Tegeler See, insbesondere den Einstrom der Oberhavel, ausreichend genau abbilden. Der Oberhaveleinstrom ist sowohl windinduziert als auch vom Abfluss der Oberhavel abhängig. Der Wind wirkt je nach Windrichtung verstärkend oder abschwächend auf den Oberhaveleinstrom. Der Tegeler See weist im Vergleich zu anderen Oberflächengewässern, die als Trinkwasserressource dienen, die höchsten bisher berichteten Gehalte an Arzneimittelrückständen auf. Die räumliche Verteilung von Carbamazepin (CBZ) und Sulfamethoxazol (SMX) wird hauptsächlich durch die Verdünnung mit Oberhavelwasser bestimmt. Nur ein geringer Teil des CBZ (40%) wird im Tegeler See eliminiert. Für SMX konnte keine Elimination festgestellt werden. Im Gegensatz dazu wird Diclofenac (DCF) im Oberflächenwasser photolytisch abgebaut (50% in den Wintermonaten, mehr als 95% im Sommer). Die Konzentrationen von DCF im Tegeler See zeigen deshalb eine hohe saisonale Variabilität. Durch Simulation von sieben Bewirtschaftungsszenarien wurde untersucht, ob mithilfe der existierenden Seeleitung und Phosphateliminierungsanlage die Konzentrationen der Arzneimittelrückstände im Tegeler See verringert werden können, ohne die erfolgreiche Seerestaurierung zu gefährden. In keinem Szenario konnten die Gehalte an Arzneimittelrückständen und Phosphor gleichzeitig auf einem akzeptablen Niveau gehalten werden. Aus diesem Grund sind ergänzende Maßnahmen notwendig, z.B. eine zusätzliche Spurenstoffentfernung im Zulauf des Sees oder eine weitere Phosphorreduzierung in der Oberhavel. / This cumulative thesis aims at (i) understanding the hydrodynamic characteristics of Lake Tegel, (ii) examining the occurrence and fate of pharmaceutical micro-pollutants in the lake, (iii) developing a modeling tool for scenario prediction, and (iv) utilizing the above findings and applying the above modeling tool to create new management strategies for Lake Tegel. The free-surface two-dimensional circulation model 2D-POM serves as an adequate tool for representing the intrusion of River Havel and the mixing intensity of both inflows, as validated by measured data. The calculations indicated that the intrusion of River Havel into Lake Tegel fluctuates with river discharge and wind, both of which can amplify or neutralize the other. Compared to other surface waters also used as drinking water resources, Lake Tegel seams to feature the highest ever reported pharmaceutical concentrations worldwide. The spatial distribution of carbamazepine (CBZ) and sulfamethoxazole (SMX) in the lake was shown to be primarily affected by dilution with water from River Havel rather than by degradation within the lake. By contrast, concentrations of diclofenac (DCL) are affected by both dilution and photodegradation. DCF showed the strongest elimination of all three pharmaceuticals and revealed significant seasonality with 50% elimination in winter and more than 95% in summer. Elimination of CBZ was 40%, while SMX did not degrade at determinable rates. Seven different management scenarios were tested to answer the question of whether the existing lake pipeline could be used to reduce the amount of pharmaceuticals in Lake Tegel without deteriorating the current phosphorus level. No scenario provided a strategy optimal for both pharmaceuticals and phosphorus. Consequently, additional efforts need to be made, such as supplementary pharmaceutical treatment of the inflow originating from the wastewater treatment plant, or phosphorus reduction in the River Havel catchment.

In dieser Dissertation wurden das Auftreten und die ökologische Bedeutung Vivianits in Süßwassersedimenten erforscht. Vivianit ist das am weitensten verbreitete reduzierte Eisenphosphatmineral, das sich in Gewässersedimenten bildet. Über die Mechanismen der Vivianitbildung in Sedimenten und die quantitative Rolle des Minerals für die Speicherung von Phosphor ist bisher wenig bekannt. Die neuen Erkenntnisse dieser Arbeit basieren auf der Entwicklung einer neuartigen Methode, die eine direkte Identifikation Vivianits mittels Röntgendiffraktometrie in Sedimenten erlaubte. Es gelang erstmalig, Vivianit in Oberflächensedimenten zu quantifizieren. Die vorliegende Arbeit zeigt, dass Vivianit signifikant, mit 10-40 %, zur Phosphorretention in Süßwassersedimenten beitragen kann. Die Untersuchung der Bildungsbedingungen Vivianits in unterschiedlichen Gewässersedimenten Norddeutschlands zeigte, dass das molare Schwefel zu Eisen Verhältnis des Sediments als ein wichtiger Indikator für die Bedingungen identifiziert, welche die Triebkräfte für die An- und Abwesenheit Vivianits darstellen. Eine Eutrophierung von Gewässern und der damit verbundene Anstieg der Sulfidproduktion kann dabei die Bildung Vivianits beeinträchtigen, und eine Abnahme des Phosphorbindungsvermögens des Sediments zur Folge haben. Die vorliegende Arbeit macht deutlich, dass eine artifizielle Erhöhung des Eisengehaltes des Sediments im Rahmen einer Seenrestaurierung eine Vivianitbildung induzieren kann und so langfristig zu einem erhöhten Phosphorrückhalt führt. Sättigungsberechnungen ergaben, dass ein hinsichtlich Vivianits übersättigtes Porenwasser kein sicheres Indiz für die Anwesenheit des Minerals ist. Die Berechnungen sind nicht in der Lage die kleinskaligen chemischen Bedingungen im Porenraum des Sediments abzubilden. Die Untersuchungen zeigen, dass die Bildung von Vivianit einen wichtigen Prozess der Phosphorbindung in Gewässersedimenten darstellt, der bislang jedoch weitestgehend vernachlässigt wurde. / In this thesis, the occurrence and environmental relevance of vivianite in freshwater sediments were explored. Vivianite is the most common reduced iron phosphate mineral which forms in sedimentary environments. Not much is known about the mechanisms which lead to vivianite formation in surface sediments, and about the quantitative role of vivianite in phosphorus sequestration. The development of a novel sediment preparation technique allowed the direct identification of vivianite by powder X-ray diffraction. Notably, for the first time, vivianite was quantified in surface freshwater sediments. The study examplifies that vivianite can significantly contribute to the phosphorus retention in surface freshwater sediments, accounting for 10-40 % of total sedimentary phosphorus. The exploration of vivianite in different surface freshwater sediments located in northern Germany revealed that the sedimentary sulphur to iron ratio is a valuable indicator for the conditions that are important drivers behind the formation or absence of vivianite. It has been demonstrated that eutrophication and the accompanied increase in sulphide production hampers vivianite formation, leading to a decreased phosphorus binding capacity of sediments through increased sediment sulphidization. The present study also revealed, that an iron addition as a measure of lake restoration can trigger vivianite formation, and significantly increases the long-term phosphorus retention of sediments. Pore water equilibrium calculations demonstrated that supersaturated pore water is not sufficient to predict the occurrence of the mineral in situ. Those calculations often fail to predict the occurrence of vivianite because they do not adequately represent chemical conditions within sediment microenvironments. In summary, the formation of vivianite in aquatic sediments constitutes an important process in phosphorus sequestration which has so far largely been ignored.

In this work, atomic scale investigation of pressure-induced transformations in the solid state have been carried out. A series of compounds including GaN, ZnO, CaF2, and AgI, in addition to elemental phosphorus have been studied. The corresponding transition mechanisms have been elucidated with a clear description of atomic displacements and intermediate structures involved therein. In the first group of compounds, the long standing debate on the transition path of the wurtzite(WZ)-to-rocksalt(RS) transition in semiconductors, GaN and ZnO was resolved using geometrical modeling combined with molecular dynamics (MD) simulations conducted in the frame of transition path sampling (TPS) method. In GaN, a two-step mechanism through a metastable intermediate phase with a tetragonal structure iT has been revealed from simulations. In ZnO, the tetragonal intermediate structure was kinetically less stable, although still part of the real transition mechanism. It appeared at the interface between WZ and RS as consequence of a layers shearing. The transition regime in ZnO was characterized by a competition between iT structure and another hexagonal intermediate with hexagonal symmetry iH. Although possible, the latter is not functional for the transition. In both cases, GaN and ZnO, two points of agreement with experiments have been revealed. The tilting of structures after transition, and the phonon mode softening associated with atomic displacements leading to the tetragonal structure iT In the second group of compounds, the investigation of transitions in superionic conductors, CaF2 and AgI, demonstrated a different and particular behavior of atomic motion under pressure. The solid-solid reconstruction of CaF2 structure was shown to be initiated and precedented by high disorder of the anionic sublattice. The percolation of fluoride ions through voids in the fluorite structure created a thin interface of liquid like state. The sparce regions caused by the departure of anions facilitates the cation sublattice reconstruction. In AgI, ion diffusion during the wurtzite/zincnlende(ZB)$rocksalt transition was more pronounced due to the extended stacking disorder WZ/ZB. The Ag+ ions profited not only from the structure of the interface but used the combination of interstitial voids offered by both phases, WZ and ZB, to achieve long diffusion paths and cause the cation sublattice to melt. Clearly, a proper account for such phenomena cannot be provided by geometry-designed mechanisms based on symmetry arguments. In phosphorus, the question of how the stereochemically active lone pairs are reorganized during the orthorhombic (PI) to trigonal (PV) structural transition was answered by means of simulations. Computation was performed at different levels theory. First, the mechanism of the transition was obtained from TPS MD simulations. MD runs were performed within density functional tight binding method (DFTB). The analysis of atomic displacements along the real transformation path indicated a fast bond switching mechanism. In a second step, the nature of the interplay between orbitals of phosphorus during the bond switching was investigated. A simultaneous deformation of lone pair and P−P bond showed a mutual switching of roles during the transformation. This interplay caused a low dimensional polymerization of phosphorus under pressure. The corresponding structure formed as zigzag linear chain of fourfold coordinated phosphorus atoms (· · ·(P(P2))n · · ·) at the interface between PI and PV phases. A further result of this work was the development of a simulation strategy to incorporate defects and chemical doping to structural transformations. On top of the transition path sampling iterations, a Monte Carlo like procedure is added to stepwise substitute atoms in the transforming system. Introducing a chemically different dopant to a pure system represents a perturbation to the energy landscape where the walk between different phases is performed. Therefore, any change in the transition regime reflects the kinetic preference of a given structural motif at times of phase formation. This method was applied to the elucidation of WZ-RS transition mechanism in the series of semiconducting compounds AlN, GaN, and InN. Simulations showed that In atoms adopt the same transformation mechanism as in GaN and favor it, while Al atoms demonstrated a significant reluctance to the path going through tetragonal intermediate iT. The difference between transition regime in mixed systems InxGa1−xN and AlxGa1−xN is in agreement with experiments on high pressure behavior of AlN, GaN, and InN. While transitions in GaN and InN are reversible down to ambient conditions, AlN is stable. The work presented in this thesis constitutes the seed of new perspectives in the understanding of pressure-induced phase transformations in the solid state, where the physics and the chemistry are brought together by means of computer simulations.

No description available.

No description available.

Ziel dieser Arbeit war es, das LISICON Li3Cr2(PO4)3 als einen Kandidaten für Hochvoltkathodenmaterialien eingehend zu charakterisieren. Dabei lag der Schwerpunkt auf den strukturellen in situ Untersuchungen mittels Synchrotronstrahlung und der Aufdeckung etwaiger limitierender Prozesse. Für diese Arbeit wurde der neue Messplatz P02.1 an der Synchrotronstrahlungsquelle PETRA III, DESY Hamburg für in situ Batterieuntersuchungen evaluiert. In Abhängigkeit von der 2D-Detektorposition können maximale q-Bereiche von bis zu 35 Å-1 oder instrumentelle Auflösungen bis zu 0,0055 Å-1 erzielt werden. Hervorzuheben ist außerdem die zeitliche Auflösung von minimal 130 ms je Diffraktogramm. Mittels galvanostatischen Messungen eines Li3Cr2(PO4)3-haltigen Komposits (80 % (w/w) Aktivmaterial) konnten zwei Lade- und ein Entlademaximum zwischen 4,7 V und 4,9 V vs. Li+/Li nachgewiesen werden. Jedoch beträgt die Coulomb-Effizienz lediglich 60 % (bei 60 mAh/g oxidativer Ladungsmenge). Eine maximale Coulomb-Effizienz von ca. 80 % wurde bei niedrigeren Temperaturen um den Gefrierpunkt gemessen. Neben strukturellen Änderungen ist eine Elektrolytzersetzung nicht auszuschließen, wobei eine mittels XPS nachgewiesene Grenzschicht zwischen Kathode und Elektrolyt diesen vor einer übermäßigen Reaktion zu schützen scheint. Erstmalig ließ sich mittels der Photoelektronenspektroskopie das aktive Redoxpaar Cr4+/Cr3+ in einer Phosphatmatrix nachweisen. Wie die in situ Untersuchungen zeigen, scheint dies mit der Bildung von Chrom-Sauerstoff-Doppelbindungen einherzugehen. Sowohl sich gegenläufig entwickelnde transständige Chromsauerstoffabstände als auch die Verringerung der Phosphorbesetzungszahlen sind starke Indizien für diese neuartige oktaedrische Koordination des Chroms. Diese als sehr stabil einzuschätzende Chromylverbindung, eine nachgewiesene stark anisotrope Kontraktion der Einheitszelle und mittels REM erkennbare Risse in den aktiven LISICON-Kristalliten werden als Hauptursachen für die relativ geringe De- und Reinterkalierbarkeit von Lithium in die Struktur des hier untersuchten Li3Cr2(PO4)3 angesehen. / Aim of this work is the investigation of a compound of the LISICON family Li3Cr2(PO4)3 as a high voltage cathode material in lithium ion batteries. This thesis focuses on the monitoring of structural fatigue mechanisms using synchrotron radiation. A new in situ experimental setup at the beamline P02.1 (PETRA III, DESY Hamburg) was evaluated. In dependence on the 2D detector position either a q-range of 35 Å-1 or an instrumental resolution of 0.0055 Å-1 were determined. A time resolution of 130 ms per diffractogram with still outstanding signal statistics shall be pointed out. By galvanostatic cycling of a Li3Cr2(PO4)3-composite (80 % (w/w) active material) partially reversible redox behavior at 4.7 V and 4.9 V vs. Li+/Li was demonstrated. A coulombic efficiency of 60 % (at 60 mAh/g oxidative charge amount) was measured at room temperature. It can be increased to 80 % at 0 °C. Electrolyte decomposition has to be considered as one possible reason for the limited electrochemical reversibility. A solid electrolyte interface, which was proven by XPS measurements, seems to protect the electrolyte against further decomposition. For the first time, the active redox pair Cr4+/Cr3+ in a phosphate matrix was proven by XPS. Most likely this behavior is accompanied by the formation of chromium-oxygen double bonds, as derived from the in situ synchrotron XRD data. Both an opposing trend in trans-positioned chromium-oxygen bond distances and the less occupied phosphorus positions give strong hints on this octahedral coordination of chromium. The chromyl group is estimated as strong bond and therewith the strongly anisotropic contraction of the unit cell and the formation of visible cracks (as found REM) in the active crystals are indicated as further reasons for the limited electrochemical reversibility for Li-intercalation and deintercalation of the investigated Li3Cr2(PO4)3.

本論文為探索性的個案研究架構，從「知識管理活動」觀點來看工廠的知識管理作法。並經由「知識管理關鍵因子」與「知識管理活動」相互關連性來探討「知識管理關鍵因子」對於個案LED廠的「知識管理活動」之影響。 對於知識管理流程的運作得到的結論有： （一）、外部知識與內隱知識同為個案企業在知識取得及創造重要來源 但由個案探討發現要讓知識取得及創造能更有效果的方法，有賴激勵制度及高階主管全力支持以促使團隊合作發展才能達到目的。 （二）、由個案跨國企業知識蓄積及分享而言，IT及網際網路科技應用是必要且影響甚鉅的，但必須搭配資深或技術人員為載體，知識蓄積及分享效果才為顯著。 （三）、教育、評核及激勵制度推動師徒制及專案團隊與跨廠區、部門合作，促進知識流通、移轉及轉換。 對於知識管理關鍵因子與知識管理流程關聯性得到結論有： 1. IT及網際網路可協助知識管理活動更加有效率及組織化。 2. 科技產品的應用對遠距離、跨區域公司的知識管理式可收事半功倍之效果。 3. 信任與自私為一體兩面，沒有相對高階的絕對支持及相對資源投入，就無以產生絕對信任。知識導入及轉移至同化是否能達效果，此為一大主因。 4. 高階主管的認知及全力支持是知識管理落實、有效執行的關鍵。 5. 相同制度用在不同地區未必可得到一致效果，因地制宜因勢利導方可收知識管理之功效。 6. 使命與榮譽感需配合評核及有效激勵制度才能成為知識傳承重要動力。 / The thesis architecture is base on exploratory case study . Base on the point view of Knowledge management to discuss the activities of factories . Base on the inter-related “ key factors of knowledge management ” and “knowledge management activities ” . We try to find the impact from“ key factors of knowledge management ” to " knowledge management activities ”in the case study. The conclusion of the knowledge management process: 1. External knowledge and implicit knowledge are equal important resource for the case company in the knowledge acquisition and creation. However, the case study found that to make knowledge acquisition and the creation can be more effective is depends on the incentive system and top managers full support to promote the development of teamwork to achieve the purpose. 2. For knowledge accumulation and sharing of multinational enterprises , IT and Internet technology application is necessary and a great influence .It will be more powerful if senior technical staff as a carrier of knowledge accumulation and sharing . 3. Education、assessment and incentive system encourage apprenticeship and project teams to work more powerful in cross-plant .That promote the circulation of knowledge, transfer and conversion. We study the relationship between key factors of knowledge management and knowledge management process . Conclusion as following： 1. IT and Internet can make knowledge management activities more efficient and organized. 2. the application of technology products on the type of long-distance, inter-regional knowledge management can get maximum effect. 3. Trust and selfishness is two side of the same coin. If there is no absolute support and the relative resources from top managers . There will be no absolute trust . It’s the main key point of knowledge import 、transfer 、 assimilation . 4. Top managers awareness and fully support to knowledge management will be the key to effective implementation. 5. The same system in different regions may not be obtained consistent results. Capitalize on the trend will be the best efficacy of knowledge management. 6. Mission and sense of honor must comply with the assessment and effective incentive system in order to become an important driving force of knowledge transmission.

The aim of the present thesis is to evaluate fast scintillator materials, in both single-crystal and powder form, for possible usage in dedicated gamma ray imaging applications as well as in X-ray imaging techniques, requiring high frame rates. Powder scintillators are traditionally used in conventional X-ray imaging due to their property to produce high resolution images. This is because laterally directed optical photons, originating from the point of X-ray interaction, are strongly attenuated by light scattering effects on powder grains. This property however is their principal drawback for routine Nuclear Medicine applications. In these applications, photon counting accuracy rather than spatial resolution is required and to this aim high transparency crystals are used. In the present study we have tried to estimate whether the use of powder phosphors can improve the image quality in a dedicated gamma-ray system where spatial resolution than sensitivity is of primary significance. Evaluation was performed in thin and thick phosphor layers easily produced in the laboratory. In addition we present a low cost solution – consisting of a thick continuous powder scintillator screen – for use in dedicated high resolution small gamma imager. The advantages and disadvantages of proposed powder detector performance were compared to two standard 3 x 3 x 5mm3 and 2 x 2 x 3mm3 pixellated CsI:Tl scintillator detector configurations. System performance in terms of system sensitivity, system spatial resolution, energy resolution and linear energy response were measured at energy of 140 keV for close-proximity nuclear emission imaging. All measurements were carried out in photon counting mode in planar imaging configuration. The investigation was divided into two parts: Fast powder scintillators: In this part, powder scintillator screens of LSO:Ce, YAG:Ce and GOS:Pr were prepared in various coating thicknesses. Measurements concerning determination of emission spectra and absolute luminescence efficiency were carried out under X-ray excitation from 22 to 140 kV. Related parameters giving informations on luminescence and intrinsic properties of the phosphors such as X-ray luminescence efficiency, quantum detection efficiency, energy absorption efficiency and intrinsic conversion efficiency were also examined. Low cost and high resolution detector module: The goal of this part was to propose and evaluate a low cost solution for detector module – consisting of a thick continuous powder scintillator screen – for use in dedicated high resolution small gamma imagers. For the latter purpose, we examined the performance of the aforementioned fast powder scintillators in the form of thick screens easily produced in the laboratory. System performance in terms of system sensitivity, system spatial resolution, energy resolution and linear energy response were measured and compared for two standard 3 x 3 x 5mm3 and 2 x 2 x 3mm3 pixellated CsI:Tl. / Ο σκοπός της παρούσας διατριβής είναι η αποτίμηση φθοριζόντων υλικών υψηλής απόκρισης, τόσο σε κρυσταλλική όσο και σε κοκκώδη μορφή για πιθανή χρησιμοποίησή τους σε συγκεκριμένους τύπους ανιχνευτικών συστημάτων Πυρηνικής Ιατρικής όπως επίσης σε συστήματα απεικόνισης με ακτίνες Χ που απαιτούν πολύ γρήγορες λήψεις ιατρικής εικόνας. Τα φθορίζοντα υλικά κοκκώδους μορφής χρησιμοποιούνται ευρύτατα στην απεικόνιση με ακτίνες-Χ λόγω της υψηλής διακριτικής ικανότητας που μπορεί να επιτευχθεί. Στην παρούσα διατριβή μελετήθηκε κατά πόσο η χρήση νέων, γρήγορων φθοριζόντων υλικών κοκκώδους μορφής μπορεί να βελτιώσει την απόδοση συγκεκριμένων τύπων ανιχνευτικών συστημάτων Πυρηνικής Ιατρικής (π.χ. dedicated small nuclear imagers), στα οποία η διακριτική ικανότητα του συστήματος είναι πιο σημαντική από την ευαισθησία. Η αποτίμηση έγινε σε φθορίζοντα μεγάλου πάχους που παρασκευάστηκαν στο εργαστήριο. Επιπρόσθετα στην παρούσα διατριβή παρουσιάζεται η εφαρμογή ενός χαμηλού κόστους συμπαγούς ανιχνευτικού υλικού κοκκώδους μορφής σε ένα εξειδικευμένο σύστημα Πυρηνικής Ιατρικής. Γίνεται συστηματική μελέτη και εκτενής αναφορά στα πλεονεκτήματα και τα μειονεκτήματα αυτού του συστήματος. Τα αποτελέσματα συγκρίνονται με αντίστοιχα αποτελέσματα που ελήφθησαν με χρήση διακριτοποιημένων σπινθηριστών τύπου CsI:Tl, μεγέθους 3 x 3 x 5mm3 και 2 x 2 x 3 mm3. Η απόδοση του συστήματος ως προς την ευαισθησία (sensitivity), τη χωρική διακριτική ικανότητα (spatial resolution) και την ενεργειακή διακριτική ικανότητα (energy resolution) αποτιμήθηκε για ενέργεια 140 keV, που αντιστοιχεί στην ενέργεια του ισοτόπου 99mTc που χρησιμοποιείται ευρύτατα σε εξετάσεις Πυρηνικής Ιατρικής. Η πειραματική μελέτη χωρίστηκε σε δύο μέρη: Φθορίζοντα υλικά κοκκώδους μορφής: Στο πρώτο μέρος της παρούσας διδακτορικής διατριβής μελετήθηκαν τα φθορίζοντα υλικά κοκκώδους μορφής LSO:Ce, YAG:Ce και GOS:Pr σε διάφορα πάχη και για μεγάλη κλίμακα ενεργειών (Υψηλή τάση λυχνίας ακτίνων-Χ από 22 kV έως 140 kV). Ανιχνευτής χαμηλού κόστους και υψηλής διακριτικής ικανότητας: Ο τελικός στόχος της παρούσας διατριβής ήταν η κατασκευή ενός ενιαίου ανιχνευτή, βασισμένου σε σπινθηριστή κοκκώδους μορφής, χαμηλού κόστους και υψηλής διακριτικής ικανότητας, κατάλληλου για χρήση σε εξειδικευμένα συστήματα Πυρηνικής Ιατρικής. Για το σκοπό αυτό μελετήθηκε η συμπεριφορά των υλικών κοκκώδους μορφής LSO:Ce, YAG:Ce και GOS:Pr υπό διέγερση ακτίνων γάμμα με ισότοπο Τεχνητίου (99mTc), ενέργειας 140 keV, που χρησιμοποιείται ευρύτατα στην Πυρηνική Ιατρική. Τα υλικά αυτά υπό την μορφή ενιαίου, μεγάλου πάχους ( ≥2mm) και διαμέτρου (9 cm), συμπαγούς ανιχνευτή αξιολογήθηκαν με τεχνικές απεικόνισης μονού φωτονίου (single photon counting mode).

Carbon nanoparticles (CNPs) have drawn great attention in the last few years owing to their unique properties such as excellent water solubility, chemical stability, inertness, low toxicity, good bio-compatibility, and tunable photo physical properties. Recently, researchers have focused on hetero atom (N, S and B) doped CNPs due to their excellent properties. These properties make the CNPs and doped CNPs as potential candidates for a wide range of applications. For example, metal ion detection in aqueous solution, bio-imaging, bio-sensing, photovoltaic devices, cleavage of deoxyribonucleic acid (DNA), and catalysis. Therefore, CNPs are alternative to inorganic semiconductor nanoparticles. However, CNPs with diameter less than 10 nm have been prepared using various approaches including top down and bottom methods. Cutting the bulk carbon from high dimensional to zero dimensional by using either physical or chemical process are classified as top down method. Bottom up method refers the conversion of organic precursor to nano-carbon by using thermal pyrolysis, microwave based hydrothermal method, cage opening of C60 molecules. In the present work, I have dealt with the facile synthesis of CNPs and different hetero atom doped carbon nanoparticles (N-CNPs, B-CNPs, and BN-CNPs) using the hydrothermal method. Based on their intriguing physical and chemical properties, these CNPs/doped-CNPs have been explored for various applications such as (i) metal-free catalysts, (ii) color tunability from red to blue and bio-imaging, (iii) ammonia sensing, (iv) white light generation, and (v) detection of picric acid (PA) in aqueous solution. Finally, I have presented 3D nanodendrites of N-CNPs and Pd NPs and their excellent catalytic mass activity for methanol electro-oxidation and ultra-fast reduction of 4-nitrophenol.