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Die zugrunde liegenden Prozesse altersbedingter Veränderungen exekutiver Funktionen werden vielfach untersucht. Für eine flexible Anpassung ist die Überwachung von Handlungen und deren Konsequenzen notwendig. Handlungsüberwachung wird mit ereigniskorrelierten Potentialen (EKP) wie der error-related negativity/error negativity (ERN/Ne) und der correct-related negativity/correct negativity (CRN) gemessen. Die Arbeit untersucht die Handlungsüberwachung bei jüngeren und älteren Erwachsenen mit dem Ziel, das Wissen über kompensatorische Strategien bei Älteren und deren Auswirkung auf die EKP Befunde zu erweitern. Ältere zeigten reduzierte ERN/Ne und größere oder vergleichbar große CRN Amplituden im Vergleich zu Jüngeren. Während nur die Jüngeren eine Reduktion der ERN/Ne mit größerer Aufgabenschwierigkeit zeigten, zeigten beide Gruppen eine ERN/Ne Reduktion unter der Instruktion, die Geschwindigkeit anstatt Genauigkeit erforderte. Nur bei Jüngeren variierte die CRN mit der Kompatibilität der Trials, mit der Aufgabenschwierigkeit und Instruktion. Ältere wiesen geringere Fehlerraten und längere Reaktionszeiten als Jüngere auf. Dieses Muster deutet auf eine kompensatorische oder strategische Anpassung in Folge von Defiziten in der Nutzung einer erfolgreichen Kombination von proaktiver und reaktiver Kontrolle hin. Es wird postuliert, dass ERN/Ne und CRN einen gemeinsamen Prozess darstellen, der allgemeine Überwachungsfunktionen reflektiert. Die ERN/Ne beinhaltet zusätzlich einen Prozess, der Fehlerüberwachung signalisiert. Daraus ergibt sich die Vermutung, dass die reduzierte ERN/Ne bei Älteren entweder auf eine Verringerung spezifischer Fehlerprozesse oder auf eine Beeinträchtigung allgemeiner Überwachungsfunktionen zurückzuführen ist. Altersbezogene Veränderungen der EKP Befunde könnten den veränderten Einsatz von kompensatorischer Kontrolle bei Älteren im Vergleich zu Jüngeren reflektieren. Dieser Frage sollte in zukünftigen Studien nachgegangen werden. / Executive functions decline with age and a growing body of research aims at investigating age-related changes of the underlying processes. One important function is to monitor actions and action outcomes, which is necessary for flexible adjustments and learning. This so-called performance monitoring can be measured with event-related potentials (ERP), namely the error-related negativity/error negativity (ERN/Ne) and the correct-related negativity/correct negativity (CRN). This work examined performance monitoring in younger and older adults with the aim to advance knowledge about compensatory strategies in older adults and their implications for ERP results. Findings revealed reduced ERN/Ne and larger or similar-sized CRN in older compared to younger adults. While only younger adults showed a decrease of ERN/Ne with higher task difficulty, both age groups showed a reduction of ERN/Ne in the speed compared to the accuracy condition. Additionally, only younger adults showed variations, in that the CRN was smaller for compatible compared to incompatible trials, in the easy compared to the difficult condition, and in the speed compared to the accuracy condition. Behaviorally, older adults had less errors and longer response latencies than younger adults. This pattern may reflect compensatory or strategic adjustments with age which may be due to deficits in the use of a successful combination of proactive and reactive control. It was further assumed that ERN/Ne and CRN share a common process that reflects general monitoring functions and ERN/Ne includes an additional process that reflects error-specific monitoring. Accordingly, the ERN/Ne attenuation in older adults is either caused by reduced error-specific processing or compromised general monitoring functions. Age-related changes in ERP findings indicate altered engagement of compensatory cognitive control in older compared to younger adults. However, this question has to be further clarified in future studies.

Global warming and developments of alternative energy technologies have become important issues nowadays. Subsequently, the concept of energy harvesting is rising because of its ability of transferring waste energy into usable energy. Thermoelectric devices play a role in this field since there is tremendous waste heat existing in our lives, such as heat from engines, generators, stoves, computers, etc. Thermoelectric devices can extract the waste heat and turn them into electricity. Moreover, the reverse thermoelectric phenomenon has the function of cooling which can be applied to refrigerator or heat dissipation for electronic devices. However, the energy conversion efficiency is still low comparing to other energy technologies. The efficiency is judged by thermoelectric figure of merit (ZT), defined by Seebeck coefficient, electrical conductivity and thermal conductivity. In order to improve ZT, thin film materials are good candidates because of their structural effects on altering ZT.    Ca3Co4O9 thin films grown by reactive radio frequency magnetron sputtering followed by post-annealing process is studied in this thesis. Structural properties of the films with the evolution of elemental ratio (Ca/Co) of calcium and cobalt have been investigated. For the investigations, three samples having elemental ratio 0.82, 0.72, and 0.66 for sample CCO1, CCO2 and COO3, respectively, have been prepared. Structural properties of the films have been investigated by X-ray diffraction (XRD) θ-2θ and pole figure analyses. Surface morphology of the films has been investigated by scanning electron microscopic (SEM) analyses. The highly oriented and phase pure epitaxial Ca3Co4O9 thin films were obtained in the end.   Mixing of ScN and CrN to obtain ScxCr1-xN solid solution thin films by DC magnetron sputtering is the other task in this thesis. Growth of ScN and CrN thin films were studied first in order to get the best mixed growth conditions. The phase shifts between ScN (111) and CrN (111) peaks were observed in mixed growth films by XRD θ-2θ measurements, indicating the formation of ScxCr1-xN. Surface morphology of the films were investigated by SEM. The (111)-oriented ScxCr1-xN thin films with decent surface smoothness grown by DC magnetron sputtering at 600 °C in pure nitrogen with bias were developed.

The saturation of the near surface layers of metals with different elements is a powerful tool to change their surface properties. In this work, structure and transport changes induced by incorporation of large amounts of nitrogen at moderate temperatures (∼370−430°C) in austenitic stainless steel are investigated. The structural study of the plasma nitrided ASS has been carried out using a combination of global (X-ray diffraction, nuclear reaction analysis) and local probe techniques (Mossbauer, X-ray absorption near edge structure, extended X-ray absorption fine structure spectroscopies). It reveals that nitriding at moderate temperatures (∼400°C) results in the nitrided layer with Fe, Cr and Ni being in different local chemical environments: Cr in the CrN-like state, Fe in the Fe4N-like state, Ni in the metallic state. The results demonstrate that the incorporation of interstitial nitrogen destabilizes homogeneous distribution of the ASS constituents, which leads to the segregation of the elements into small zones rich in Cr and Ni and provide strong evidence that the decomposition is of a spinodal nature. These experimental findings contradict the widely accepted view that the phase formed during nitriding at moderate temperatures is a homogeneous supersaturated nitrogen solid solution. The nitrogen atomic transport study has been carried out by using ion beam nitriding of single-crystalline stainless steel, and the issues of the influence of the crystalline orientation, nitriding temperature, ion flux and ion energy are addressed. The diffusion coefficients have been extracted from the fitting of the nitrogen depth profiles by using the trapping-detrapping model. It is shown that the crystalline orientation plays a significant role in nitrogen diffusion: the penetration depth is largest, intermediate and lowest for the (001), (110) and (111) orientation, respectively. The pre-exponential factor D0 varies by two orders of magnitude depending on the orientation, while the activation energy E is similar (∼1.1 eV) for the (111) and (110) orientations and higher for the (001) orientation (∼1.4 eV). It is found that the nitrogen ion energy and the flux have the effect on the nitrogen transport in the bulk with higher energies (or fluxes) showing larger diffusion coefficients. The ion energy effect is more pronounced for the (001) than for the (111) orientation, while the flux effect is similar in both orientations. In addition, the diffusivity during post-nitriding thermal annealing without ion irradiation is found to be independent of the crystalline orientation. The observed radiation enhanced diffusion and anisotropy are discussed on the basis of nitrogen incorporation induced changes in the matrix structure (ASS decomposition and formation heterogeneous structure), ion bombardment induced effects (defects, localized vibrations) and correlated diffusion.

The saturation of the near surface layers of metals with different elements is a powerful tool to change their surface properties. In this work, structure and transport changes induced by incorporation of large amounts of nitrogen at moderate temperatures (∼370−430°C) in austenitic stainless steel are investigated. The structural study of the plasma nitrided ASS has been carried out using a combination of global (X-ray diffraction, nuclear reaction analysis) and local probe techniques (Mossbauer, X-ray absorption near edge structure, extended X-ray absorption fine structure spectroscopies). It reveals that nitriding at moderate temperatures (∼400°C) results in the nitrided layer with Fe, Cr and Ni being in different local chemical environments: Cr in the CrN-like state, Fe in the Fe4N-like state, Ni in the metallic state. The results demonstrate that the incorporation of interstitial nitrogen destabilizes homogeneous distribution of the ASS constituents, which leads to the segregation of the elements into small zones rich in Cr and Ni and provide strong evidence that the decomposition is of a spinodal nature. These experimental findings contradict the widely accepted view that the phase formed during nitriding at moderate temperatures is a homogeneous supersaturated nitrogen solid solution. The nitrogen atomic transport study has been carried out by using ion beam nitriding of single-crystalline stainless steel, and the issues of the influence of the crystalline orientation, nitriding temperature, ion flux and ion energy are addressed. The diffusion coefficients have been extracted from the fitting of the nitrogen depth profiles by using the trapping-detrapping model. It is shown that the crystalline orientation plays a significant role in nitrogen diffusion: the penetration depth is largest, intermediate and lowest for the (001), (110) and (111) orientation, respectively. The pre-exponential factor D0 varies by two orders of magnitude depending on the orientation, while the activation energy E is similar (∼1.1 eV) for the (111) and (110) orientations and higher for the (001) orientation (∼1.4 eV). It is found that the nitrogen ion energy and the flux have the effect on the nitrogen transport in the bulk with higher energies (or fluxes) showing larger diffusion coefficients. The ion energy effect is more pronounced for the (001) than for the (111) orientation, while the flux effect is similar in both orientations. In addition, the diffusivity during post-nitriding thermal annealing without ion irradiation is found to be independent of the crystalline orientation. The observed radiation enhanced diffusion and anisotropy are discussed on the basis of nitrogen incorporation induced changes in the matrix structure (ASS decomposition and formation heterogeneous structure), ion bombardment induced effects (defects, localized vibrations) and correlated diffusion.

Various nitrides, such as chromium nitride and titanium nitride, find extensive use in cutting tools, micromechanical devices, and medical implants due to their exceptional physical, mechanical, and chemical properties. These coatings exhibit superior hardness compared to high-speed steel and cemented carbide along with notable protective capabilities against corrosion and wear. These coatings have been successfully used to enhance the properties of cemented carbide and steel tools while safeguarding their surfaces. By adjusting deposition parameters like N2 gas pressure, the properties of PVD coatings can be tailored to effectively withstand specific dominant wear modes during machining. The study investigates and demonstrates that CrN coatings can be specifically engineered to have distinct mechanical and tribological properties by adjusting the N2 gas pressure, which enhances machining performance in cases where BUE formation occurs. A comprehensive coating characterization was conducted for each CrN coating studied. Wear performance assessments of the various CrN-coated WC tools were carried out during dry finish turning of SS 304. Additionally, high temperature coating characterization was performed for the best-performing in house deposited coating (nitrogen gas pressure of 4 Pa, bias voltage of -50 V) and a commercial coating, up to 450°C. The results highlighted the influence of N2 gas pressure on the structural, mechanical, and tribological properties of CrN coatings. The findings indicate that coatings with a comparatively low H/E ratio (while maintaining higher elastic modulus values), low roughness, moderate residual stress, high plasticity index, and high toughness exhibited superior performance when machining sticky materials and in high-temperature applications prone to adhesive wear and built-up edge (BUE) formation. Furthermore, high-temperature studies confirmed that the in-house coating retained a low H/E ratio, high plasticity index, high toughness, and low roughness, without compromising the hardness or elastic modulus values. In contrast, the commercial coating failed to retain its properties at higher temperatures. These high-temperature studies provide valuable insights for selecting CrN coatings tailored for machining materials that tend to adhere to the cutting tool and for high-temperature applications. / Dissertation / Master of Applied Science (MASc) / Coating properties such as hardness, residual stress, adhesive behaviour, elastic modulus, and roughness significantly affect tool performance and wear patterns, besides machining parameters and conditions. This research focuses on CrN coatings deposited by PVD cathodic arc deposition, adjusting the N2 gas pressure while keeping bias voltage constant. The research investigates and illustrates that CrN coatings can be specifically tailored (by adjusting the N2 gas pressure) to possess unique mechanical, and tribological properties that ameliorate machining performance in scenarios involving BUE formation. Three CrN coatings were deposited using the PVD technique by varying the N2 gas pressure. A thorough coating characterization was conducted for each of three in house deposited coatings and one commercially available coating. The wear behaviour of different CrN-coated WC tools was evaluated during dry finish turning of SS 304 to identify the best-performing coating. Lastly, high-temperature coating characterization was performed up to 450 ˚C for one in-house deposited coating (nitrogen gas pressure of 4 Pa, bias voltage of -50 V) and one commercial coating. The results showed that a coating that has low H/E ratio (without compromising elastic modulus), high plasticity index, high toughness, moderate residual stress and low roughness effectively minimizes issues related to sticking and BUE formation and retains coating properties at high temperatures.

Le groupe HEF (Hydromécanique Et Frottements), premier équipementier et façonnier français en traitements de surface par plasmas hors microélectronique, utilise dans ses procédés industriels des sources plasma micro-onde multi-dipolaires fonctionnant sur le principe de la résonance cyclotronique électronique pour la réalisation de dépôts de type DLC par PACVD, et pour l'assistance ionique à la croissance de couches CrN par pulvérisation magnétron réactive. Suite à la présentation de l'utilisation de ces sources pour des dépôts de DLC et des ajustements nécessaires pour leur mise en œuvre industrielle, les travaux de cette thèse portent sur le développement de nouvelles sources plasma micro-onde en vue d'améliorer l'uniformité des traitements de surface dans le volume du réacteur ainsi que la productivité des réacteurs plasma pour le dépôt de ces couches. Les résultats obtenus sont intéressants puisque le développement d'une source étendue a permis d'augmenter la vitesse de dépôt des couches DLC sans dégradation des propriétés mécaniques et d'obtenir une uniformité similaire à celle obtenue avec les sources multi-dipolaires en utilisant deux fois moins d'applicateurs micro-onde. Les réflexions portant sur l'amorçage du plasma ont permis d'identifier les voies d'amélioration de cette source pour valider son utilisation en milieu industriel. L'utilisation de cette source étendue pour l'assistance ionique à la croissance de couches telles que le nitrure de chrome CrN par pulvérisation magnétron réactive a démontré un potentiel intéressant en termes de propriétés mécaniques obtenues et a permis d'identifier des axes de développement de cette configuration.

Radio spectrum has become increasingly scarce due to the proliferation of new wireless communication services. This problem has been exacerbated by fixed bandwidth licensing policies that often lead to spectral underutilization. Cognitive radio networks (CRN) can address this issue using flexible spectrum management that permits unlicensed (secondary) users to access the licensed spectrum. Supporting real-time quality-of-service (QoS) in CRNs however, is very challenging, due to the random spectrum availability induced by the licensed (primary) user activity. This thesis considers the problem of real-time voice transmission in CRNs with an emphasis on secondary network ``friendliness''. Friendliness is measured by the secondary real-time voice capacity, defined as the number of connections that can be supported, subject to typical QoS constraints. The constant bit rate (CBR) air interface case is first assumed. An offline scheduler that maximizes friendliness is derived using an integer linear program (ILP) that can be solved using a minimum cost flow graph construction. Two online primary scheduling algorithms are then introduced. The first algorithm is based on shaping the primary spectral hole patterns subject to primary QoS constraints. The second applies real-time scheduling to both primary traffic and virtual secondary calls. The online scheduling algorithms are found to perform well compared to the friendliness upper bound. Extensive simulations of the primary friendly schedulers show the achievable secondary voice capacity for a variety of parameters compared to non-friendly primary scheduling. The thesis then considers the variable bit rate (VBR) air interface option for primary transmissions. Offline and online approaches are taken to generate a primary VBR traffic schedule that is friendly to secondary voice calls. The online VBR schedulers are found to perform well compared to the friendliness upper bound. Simulation results are presented that show the effect of the primary traffic load and primary network delay tolerance on the primary network friendliness level towards potential secondary voice traffic. Finally, secondary user friendliness is considered from an infrastructure deployment point of view. A cooperative framework is proposed, which allows the primary traffic to be relayed by helper nodes using decode-and-forward (DF) relaying. This approach decreases the primary traffic channel utilization, which, in turn, increases the capacity available to potential secondary users. A relay selection optimization problem is first formulated that minimizes the primary channel utilization. A greedy algorithm that assigns relay nodes to primary data flows is introduced and found to perform well compared to the optimum bound. Results are presented that show the primary network friendliness for different levels of primary channel utilization. / Dissertation / Doctor of Philosophy (PhD)

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