Techn. Universiẗat, Diss., 2002--Darmstadt.

Universiẗat, Diss., 2003--Jena.

Universiẗat, Diss., 2004--Jena.

Η παρούσα εργασία πραγματεύεται τόσο από θεωρητικής πλευράς το φαινόμενο της διεθνοποίησης και των εταιρικών στρατηγικών διεθνοποίησης, αλλά και πως αυτές εφαρμόζονται στην περίπτωση του Ομίλου ΤΙΤΑΝ. ‘Ετσι εξετάζουμε εκτενώς τις εταιρικές στρατηγικές διεθνούς επέκτασης του Ομίλου, ώστε αφ’ ενός να θεμελιώσει ένα γνωστικό υπόβαθρο στη μελέτη οργανισμών υπό το πρίσμα της διεθνοποίησης και αφ’ετέρου να εξακριβώσει την ύπαρξη συσχέτισης μεταξύ των θεωρητικών προσεγγίσεων και των ρεαλιστικών πρακτικών. Ο Όμιλος επιλέχθηκε για την μελέτη διεθνοποίησης και στρατηγικών ανάπτυξης μιας εταιρίας στο διεθνές περιβάλλον, λόγω της διαχρονικής εστίασης του σαν εταιρία σε διεθνοποίηση των δραστηριοτήτων του και στην γεωγραφική διαφοροποίησης του στις δραστηριότητες του. Επιπρόσθετα, ο ΤΙΤΑΝΑΣ αποτελεί την παλαιότερη τσιμεντοβιομηχανία της Ελλάδας και μια πολύ ισχυρή δύναμη στον κλάδο των δομικών υλικών τόσο στην εγχώρια όσο και στην παγκόσμια αγορά. Η έρευνα και η μελέτη της εργασίας μας βασίστηκε σε διάφορες πηγές πληροφοριών όπως το διαδίκτυο, τα πανεπιστημιακά βιβλία, σχετικά οικονομικά άρθρα καθώς και από συνεντεύξεις από στελέχη της εταιρίας ΤΙΤΑΝ και από τα οποία καταφέραμε να συγκεντρώσουμε αρκετά στοιχεία για την στρατηγική διεθνοποίησης που ακολουθεί η εταιρία ΤΙΤΑΝ. / -

Tillverkning av slutprodukter med additiv tillverkning   blir allt vanligare. Slutprodukter har högre krav på detaljens mekaniska   egenskaper än prototyper gör. Forskning har visat att porositeten är av stor   betydelse för en detaljs hållfasthet. Med additiv tillverkning finns goda   möjligheter för direkt processövervakning och kontrollsystem. Inom electron   beam melting finns sådana system men de saknas en validering av resultatet   från dom systemen. I de här arbetet har prover med designade defekter   tillverkats. LayerQam bilder från tillverkningen har analyserats med Defect   Detector. Data från analysen har visualiserats. Resultatet har studerats samt   att det har tagits fram en Defect Detector-analys med högre precision.   Utvalda prover har undersökts i ett tvärsnitt med optisk mikroskopi samt i 3D   med mikrotomografi. Undersökningarna har jämförts med varandra, de tyder på   att Defect Detector har brister i sin bedömning av densiteten. De designade   defekterna har en överskattad storlek samt brister i kompensation av   förvrängningen i synfältet i bilderna. / <p>Betyg: 180827</p>

An Ab Initio/RRKM study of the reaction mechanism and product branching ratios of neutral-radical ethynyl (C2H) and cyano (CN) radical species with unsaturated hydrocarbons is performed. The reactions studied apply to cold conditions such as planetary atmospheres including Titan, the Interstellar Medium (ISM), icy bodies and molecular clouds. The reactions of C2H and CN additions to gaseous unsaturated hydrocarbons are an active area of study. NASA’s Cassini/Huygens mission found a high concentration of C2H and CN from photolysis of ethyne (C2H2) and hydrogen cyanide (HCN), respectively, in the organic haze layers of the atmosphere of Titan. The reactions involved in the atmospheric chemistry of Titan lead to a vast array of larger, more complex intermediates and products and may also serve as a chemical model of Earth’s primordial atmospheric conditions. The C2H and CN additions are rapid and exothermic, and often occur barrierlessly to various carbon sites of unsaturated hydrocarbons. The reaction mechanism is proposed on the basis of the resulting potential energy surface (PES) that includes all the possible intermediates and transition states that can occur, and all the products that lie on the surface. The B3LYP/6-311g(d,p) level of theory is employed to determine optimized electronic structures, moments of inertia, vibrational frequencies, and zero-point energy. They are followed by single point higher-level CCSD(T)/cc-vtz calculations, including extrapolations to complete basis sets (CBS) of the reactants and products. A microcanonical RRKM study predicts single-collision (zero-pressure limit) rate constants of all reaction paths on the potential energy surface, which is then used to compute the branching ratios of the products that result. These theoretical calculations are conducted either jointly or in parallel to experimental work to elucidate the chemical composition of Titan’s atmosphere, the ISM, and cold celestial bodies.

Several different mechanisms leading to the formation of (substituted) naphthalene and azanaphthalenes were examined using theoretical quantum chemical calculations. As a result, a series of novel synthetic routes to Polycyclic Aromatic Hydrocarbons (PAHs) and Nitrogen Containing Polycyclic Aromatic Compounds (N-PACs) have been proposed. On Earth, these aromatic compounds originate from incomplete combustion and are released into our environment, where they are known to be major pollutants, often with carcinogenic properties. In the atmosphere of a Saturn’s moon Titan, these PAH and N-PACs are believed to play a critical role in organic haze formation, as well as acting as chemical precursors to biologically relevant molecules. The theoretical calculations were performed by employing the ab initio G3(MP2,CC)/B3LYP/6-311G** method to effectively probe the Potential Energy Surfaces (PES) relevant to the PAH and N-PAC formation. Following the construction of the PES, Rice-Ramsperger-Kassel-Markus (RRKM) theory was used to evaluate all unimolecular rate constants as a function of collision energy under single-collision conditions. Branching ratios were then evaluated by solving phenomenological rate expressions for the various product concentrations. The most viable pathways to PAH and N-PAC formation were found to be those where the initial attack by the ethynyl (C2H) or cyano (CN) radical toward a unsaturated hydrocarbon molecule led to the formation of an intermediate which could not effectively lose a hydrogen atom. It is not until ring cyclization has occurred, that hydrogen elimination leads to a closed shell product. By quenching the possibility of the initial hydrogen atom elimination, one of the most competitive processes preventing the PAH or N-PAC formation was avoided, and the PAH or N-PAC formation was allowed to proceed. It is concluded that these considerations should be taken into account when attempting to explore any other potential routes towards aromatic compounds in cold environments, such as on Titan or in the interstellar medium.

Titanium is thanks to its high corrosion resistance and biocompatibility widely used in medicine. Ti alloys are used due to their superior mechanical properties instead of pure Ti for load carrying components. Ti alloys are often alloyed with elements which are toxic for human body and further increase cost of Ti products. Main focus of current development is to create pure Ti with better mechanical properties. It can be done by reducing grain size by processes based on severe plastic deformation. The aim of this work is to evaluate fatigue properties as well as fatigue crack initiation and propagation mechanism of Ti grade 2 with the ultrafine grained structure. After microstructure analysis, fatigue tests with symmetrical loading were executed. Fracture surfaces of ultrafine grained Ti grade 2 were observed after fatigue tests for identification of failure mechanism. Results were compared with those for course-grained Ti grade 2.

The thesis is focused on the surface treatment used for the preparation of aluminium alloys for the adhesive bonding. The theoretical part can be divided into three chapters. The first of them deals with aluminium alloys, the second one speaks about the adhesive bonding. The surface treatment itself, especially the conversion coating issues, is discussed in the last chapter. The experimental part is focused on the optimalization of a two-step titanium and zirconium based conversion coating technology. In the first part, the aluminium alloy is analysed by the glow discharge optical emission spectroscopy. The second part of the experiment deals with the first step of the technology, acidic deoxidation. The objective was to examine the influence of the exposure time on the morphology of the alloy surface and the shear strength of adhesive joints. In the last part of the experiment, the conversion coatings are prepared and characterised by the scanning electron microscopy and energy dispersive spectroscopy.

In the present work, the abnormal glow discharge at atmospheric pressure was generated in the nitrogen-methane (1 to 5 %) gaseous mixtures related to the atmosphere of Titan. The discharge itself was monitored by optical emission spectrometry that confirmed presence of active nitrogen species and various radicals formed from methane. Besides them, the CN spectral bands were observed. Intensities of all light emitting species were studied in the dependence on applied power and composition of nitrogen-methane mixture. The rotational temperature of about 2000 K was calculated from the second positive nitrogen system. The vibrational temperature also obtained from neutral nitrogen molecule increased nearly directly with methane from 3000 K (1 % CH4) to 3600 K (5 % CH4). In the contrary, vibrational temperature obtained from nitrogen molecular ion decreased with methane in the gaseous mixture and increased with applied discharge power from 3700 K to 4200 K. The same trend showed the vibrational temperature calculated from violet system of CN with value from 4600 K to 5800 K. The stable discharge products were analysed by proton transfer time of flight mass spectrometry of the exhausting gas. Presence of many aliphatic and some aromatic hydrocarbons was confirmed as well as quite a lot of amino and cyano compounds. Increasing concentrations of methane have produced more substances with higher molecular weight and less simple substances that were likely to be consumed on more complex substances. Their relative intensities were determined under the same conditions as optical emission spectra were collected.