Photoluminescence related to transition metal and carbon defects in GaN

Galliumnitrid (GaN) ist ein Schlüsselmaterial zur Produktion von elektronischen Hochfrequenz- und Hochleistungsbauelementen sowie Leuchtdioden. Zum Erreichen der optimalen Bauelementleistung ist ein tiefgreifendes Verständnis sowie die Kontrolle von Punktdefekten unabdingbar um die elektrischen und optischen Substrateigenschaften präzise einzustellen. Im Rahmen dieser Arbeit wurden Punktdefekte in GaN mittels Photolumineszenz (PL)-spektroskopie untersucht. Häufige Übergangsmetallverunreinigungen (Fe, Mn und Cr) wurden anhand ihrer internen Übergänge, die sich durch scharfe Lumineszenz- und Absorptionslinien im nahen Infrarot auszeichnen, identifiziert. Mn und Cr wurden als Ursprung für ungewollte Substratfärbungen bestimmt. Teilweise Entfärbung konnte durch Mn-Si-Kodotierung erreicht werden. Der Zusammenhang zwischen Absorption und Emission des Cr-Zentrums wurde durch polarisationsabhängige PL-Anregungsspektroskopie analysiert. Weiterhin wurde der Einfluss von Kohlenstoffdotierung auf die Eigenschaften von GaN-Substraten durch PL- und PL-Anregungsspektroskopie untersucht. Eine neue Emissionsbande um 1,62 eV, die am effizientesten bei 2,7 eV angeregt wird, wurde für hochdotiertes GaN:C beobachtet und einem internen Übergang C_N-C_Ga-C_N-Komplexen zugeschrieben.Gallium nitride (GaN) is a key material for the production of high frequency and high power electronics as well as light emitting diodes. Optimum device performance requires a profound understanding and control of the point defect formation in order to determine the electrical and optical substrate properties. Within this thesis, photoluminescence (PL) spectroscopy was applied to analyze point defects in GaN. Common transition metal impurities (Fe, Mn and Cr) were identified by their internal transitions characterized by sharp luminescence and absorption lines in the near infrared region. Among them, Mn and Cr were shown to be the origin of undesirable substrate coloration. Partial decoloration was achieved by an Mn-Si codoping approach. The relationship of absorption and emission processes of the Cr impurity center was further analyzed by polarization dependent PL excitation spectroscopy. Furthermore, the impact of C-doping on GaN substrate properties was investigated by PL and PL excitation spectroscopy. A new emission band around 1.6 eV, most efficiently excited at 2.7 eV, was reported for highly C-doped GaN and proposed to originate from an internal transition of C_N-C_Ga-C_N complexes

Young adults’ images of abstaining and drinking: Prototype dimensions, correlates and assessment methods

This research investigated contents of actor and abstainer prototypes with regard to young adults’ social drinking combining quantitative and qualitative approaches (adjective ratings, N = 300; open answers, N = 90). Exploratory and confirmatory factor analyses yielded two factors (sociability/hedonism, responsibility) in both prototypes, confirmed by qualitative data. Given the importance for intention and willingness to drink alcohol, interventions should focus on the factor ‘sociability/hedonism’ of the actor and the abstainer prototype to reduce heavy drinking; addressing ‘responsibility’ may be ineffective. Participants’ evaluations appeared to be less prone to mean tendencies subsequent to open answers compared with adjective scales

Do psychological variables mediate sex differences in young adults' alcohol use?

This study applied an extended theory of planned behavior to test whether psychological variables mediate sex differences in alcohol consumption in social contexts. Questionnaires of 300 young adults (urban, mean age 25 years, 49% female) were collected in 2007 prior to a sociable drinking occasion; consumption data were obtained through telephone interviews thereafter. The multiple-path mediation model was analyzed using structural equation modeling. Sex differences in alcohol consumption, which were considerable, were partly mediated by the significant specific indirect effects of subjective norms through intention and of self-efficacy through both intention and willingness. Body weight was not a significant mediator. Limitations are noted and implications for future research are discussed

Gender-related traits as predictors of alcohol use in male German and Spanish university students

This study examined instrumental (masculine stereotyped) and expressive (feminine stereotyped) personality traits and alcohol use among men from Germany and Spain. Participants were 161 male university students (76 German, M-age=23 years; 77 Spanish, M-age=22 years), who completed either a daytime or a nighttime drinking questionnaire, each including a Short Form of the Bem Sex Role Inventory. Poisson regression analyses with latent predictors were conducted. The trait factors and their interactions with nationality predicted daytime and nighttime alcohol use. The results add support to the assumption that alcohol use is associated with the construction of masculinity and that internalization of traditionally female attributes protects against health-risk behaviors such as alcohol consumption

The role of gut microbiome-associated metabolites in cardiometabolic diseases

Introduction Intestinal flora is essential for cardiometabolic health. Changes of gut microbiome composition are associated with numerous disease states, including cardiovascular and cardiometabolic. Multiple gut microbial metabolites have been shown to impact cardiometabolic physiology in animal and human studies. Here we examined the influence of gut microbiota as well as of its metabolite propionate on cholesterol homeostasis in mice. Furthermore, we investigated a potential role of the gut microbiome for cholesterol lowering effects of atorvastatin. Methods To address these objectives we used wild type and hypercholesterolemic mice. Mice with intact or antibiotics depleted gut microbiome were put on standard control or high fat diet for six weeks. From week three mice were orally applied either control vehicle, propionate or atorvastatin once daily. After six weeks mice were sacrified and feces, organs and blood were collected. Blood lipids were determined by high performance liquid chromatography. To demonstrate community composition of the gut microbiome of the respective groups, 16S rRNA gene analysis was performed. Semiquantitative protein expression of hepatic and intestinal proteins were assessed via Western Blot. In vitro inhibitory properties of propionate on HMGCR were examined using an enzyme activity assay and hepatic cell line. Statistical analyses were performed by 1-way ANOVA followed by post hoc Tukey’s multiple comparison test or students t test. Results Gut microbiome composition was changed upon high fat diet compared to control diet in wild type mice. Propionate and atorvastatin modulated gut microbiome composition at phylum level in conventional mice. Hyperlipidemic abiotic ApoE-/- mice showed elevated LDL-level compared to mice with intact gut microbiome. Orally applied propionate lowered LDL-level in high fat diet fed ApoE-/- mice microbiota-dependent. To identify underlying pathways key enzymes in cholesterol metabolism were investigated on protein level. Atorvastatin showed a microbiota-dependent regulation of proteins, while this was not observed for propionate. Propionate did not impact HMGCR enzyme activity nor protein expression in HepG2 cells. Conclusion Our findings support a regulatory property of the gut microbiome for cholesterol homeostasis. We found that orally administered gut microbiota-derived metabolite propionate reduced LDL-level in HFD fed hypercholesterolemic mice. As one potential underlying mechanism we found a changed gut microbiome composition. Furthermore, we demonstrated that atorvastatin-treatment had a microbiota-dependent regulatory effect on blood lipids and changed gut microbiome composition. Our results provide novel insights into potential microbiota-related mechanisms in cholesterol metabolism and indicate the gut microbiome as a treatment target in dyslipidemia and cardiovascular prevention.Einleitung Die intestinale Flora ist integraler Bestandteil kardiometabolischer Gesundheit. Veränderungen des Darmmikrobioms sind mit kardiometabolischen Erkrankungen assoziiert. Ziel dieser Arbeit ist es, den Einfluss des von Darmmikrobiom und Propionat, einem Metaboliten des Darmmikrobioms, im Cholesterinmetabolismus im Tiermodell zu untersuchen. Zudem untersuchten wir den Einfluss des Darmmikrobioms für cholesterinsenkende Effekte einer Statintherapie mit Atorvastatin. Methoden Wir verwendeten Wildtyp- und Apolipoprotein E Knockout (ApoE-/-) Mäuse als etabliertes Mausmodell der Hypercholesterinämie. Mäuse mit intaktem oder durch Antibiotikagabe eradiziertem Darmmikrobiom (sekundär abiotisch) erhielten über 6 Wochen Standard- oder Hochfettdiät. Ab Woche 3 wurden die Mäuse täglich mit Propionat, Atorvastatin oder einer Kontrolllösung gavagiert. Nach 6 Wochen wurden die Mäuse getötet und Fäzes, Blut und Organe gesammelt. Blutlipide wurden durch Hochleistungsflüssigkeitschromatographie bestimmt. Mittels 16srRNA Genanalyse erfolgte die Analyse der Darmmikrobiomzusammensetzung auf OTU-Ebene. Expression hepatischer und intestinaler Schlüsselproteine des Cholesterinmetabolismus wurden via Western Blot untersucht. Potentielle inhibitorische Effekte von Propionat auf HMGCR wurden mittels Enzym-Aktivitäts-Assay und einer hepatischen Zelllinie untersucht. Statistische Analysen erfolgten mittels 1-way ANOVA, gefolgt von einem post hoc Tukey’s oder Students T-Test. Ergebnisse Die Darmmikrobiomzusammensetzung wurde in Wildtypmäusen durch Diät auf Ebene der Bakteriengruppen beeinflusst. Propionat und Atorvastatin zeigten Einfluss auf Phylumebene. Hyperlipidämische ApoE-/- Mäuse ohne Darmmikrobiom zeigten höhere Plasmaspiegel von LDL als konventionelle Vergleichstiere. Unter oraler Propionatzufuhr zeigten Hochfettdiät gefütterte ApoE-/- Mäuse signifikant reduzierte LDL-Spiegel, wenn das Mikrobiom intakt war. Propionat hatte keinen Einfluss auf LDL-Spiegel sekundär abiotischer Tiere. Atorvastatin, jedoch nicht Propionat, wies eine Mikrobiom-abhängige Regulation hepatischer und intestinaler Schlüsselproteine des Cholesterinmetabolismus auf. Propionat zeigte keinen Einfluss auf die HMGCR-Aktivität. Inkubation von HepG2 Zellen mit Propionat führte zu keiner Expressionsveränderung von HMGCR und HMGCS1. Diskussion Unsere Ergebnisse unterstreichen den regulatorischen Effekt des Darmmikrobioms auf den Cholesterinmetabolismus. Propionatzufuhr führte zur Senkung der LDL-Blutspiegel hyperlipidämischer Mäuse unter Hochfettdiät mit intaktem Mikrobiom. Als potentiellen Mechanismus identifizierten wir eine veränderte Darmmikrobiomzusammensetzung. Zudem sahen wir eine Modulation des Mikrobioms durch Atorvastatin sowie Darmmikrobiom-abhängige Regulation des cholesterinsenkenden Effektes von Atorvastatin. Diese Ergebnisse könnten dazu beitragen neuartige, Darmmikrobiom-basierte Konzepte zur Prävention und Behandlung kardiometabolischer Erkrankungen zu entwickeln

What Works in School? Expert and Novice Teachers’ Beliefs about School Effectiveness

In 2009, John Hattie first published his extensive metasynthesis concerning determinants of student achievement. It provides an answer to the question: “What works in school?” The present study examines how this question is answered by pre- and in-service teachers, how their beliefs correspond to the current state of research and whether they differ according to the teachers' level of expertise. Thus, it takes on a novel approach as it draws on data from two sources in the field of education -- empirical research and teachers’ beliefs -- and examines their similarities and differences. The teachers’ beliefs were elicited by asking N = 729 participants to estimate the effect sizes of several determinants of student achievement. Those were compared to the empirical effect sizes found by Hattie (2009). Profile correlations showed that expert teachers’ beliefs are more congruent with current research findings than those of novice teachers. We further examined where expert and novice teachers’ beliefs differ substantially from each other by using confirmatory factor analysis (CFA) and comparing group means in latent variables. Our findings suggest that teachers’ beliefs about school effectiveness are related to professional experience: Expert teachers showed a stronger overall congruence with empirical evidence, scoring higher in achievement-related variables and lower in variables concerning surface- and infrastructural conditions of schooling as well as student-internal factors. Results are discussed with regard to teacher-education practices that emphasize research findings and challenge existing beliefs of (prospective) teachers

Unfamiliar face recognition: How we perceive and remember new faces

Most humans are experts in recognizing faces of familiar individuals, but are poor at individuating unfamiliar faces. The discrepancy between these two types of face recognition suggests qualitative differences in the perceptual encoding and memory storage of familiar and unfamiliar faces, yet little is known about the neural basis of these differences. In the present thesis, behavioural and event-related brain potential (ERP) measures were combined to investigate the mechanisms that underlie the perception and recognition of unfamiliar faces. The first two experiments investigated whether memory traces for unfamiliar faces are based on low-level view-dependent or more high-level view-independent codes. Results provide strong evidence for a qualitative change from strictly view-dependent to view-independent representations in visual face memory as initially novel unfamiliar faces become more familiar. A second series of three experiments examined whether identity-specific cues are processed in an optional or obligatory fashion. Findings suggest that the perception of facial identity is strongly task-dependent (i.e., optional), even for famous faces, but can also show a degree of mandatory processing when identity is task-irrelevant. The sixth study examined the persistence of perceptual memories of unfamiliar faces and revealed a substantial weakening of face representations in visual working memory over short periods of time. The final experiment investigated the neural basis of developmental prosopagnosia (DP). Results demonstrated spared identity-sensitive processing in DP participants, indicating that their face recognition deficits do not always result from severely disrupted visual face recognition processes. However, despite evidence for perceptual learning of invariant aspects of face structure, these processes seemed to be inefficient in individuals with DP. Taken together, this thesis explored how we perceive and remember individual unfamiliar faces. Results indicate that unfamiliar face recognition is mediated by fast and flexible (i.e., strongly task-dependent) identity-specific visual processes, which rapidly become view-invariant during face learning