The Influence of Social Relationships on Conduct Problems in School Context - Does School Engagement Matter?

There has been an increase in the prevalence of problem behavior during adolescence over the last decades. Thereby, studies have found that social bonds and relationships as well as school engagement as a form of connectedness play an important protective role. However, less is know whether school engagement is as a potential mediator in the association of social relationships with peers and teachers and conduct problems. The current study examined this interplay in a large non-clinical sample of students (N= 1.088; MAge= 13.7 SD=0.53 at T1; N= 845; Mage = 15.32, SD = .49 at T2) in secondary schools in Brandenburg, Germany. Structural Equation Modeling (SEM) was used to test the mediating effect from school engagement in the association between students' social relationships in early adolescence and conduct problems in middle adolescence. The results show that school engagement function as full mediator in the association of both student-student relationships and teacher-student relationships at T1 and conduct problems at T2. This highlights that fostering school engagement in early adolescence might be an essential starting point for prevention and intervention strategies of conduct problems in middle adolescence

A Model of Boys' Body Image in Early Adolescence

"Das Hauptziel dieser Studie galt der Identifizierung essentieller Faktoren der Körperbildentwicklung in einer nicht-klinischen Stichprobe von Jungen unter Berücksichtigung möglicher Einflüsse durch Peers, Familie und Medien. Es wurden semi-strukturierte Leitfadeninterviews mit 14 früh-adoleszenten Jungen (Altersrange von 10-12 Jahren) geführt, die zufällig aus den Teilnehmern einer größeren quantitativen Fragebogenstudie (N=167) an Grundschulen in Berlin ausgewählt wurden. Mittels thematischer Analyse konnten zwei Hauptthemen identifiziert werden: (1) sozialer Vergleich (beinhaltet die beiden Subthemen Selbst-Verbesserung und Selbst-Erhöhung) und (2) Internalisierung (beinhaltet die beiden Subthemen behaviorale und kognitive Dimensionen). An Hand der Ergebnisse wurde schließlich ein finales Modell erstellt, das die Konzeptualisierung des Körperbildes von Jungen in der frühen Adoleszenz abzubilden sucht." (Autorenreferat)"The major aim of this study was to explore and promote a deeper understanding of the essential contributing factors to body image development in a non-clinical sample of boys, including the roles played by peers, family, and media. In this study, semi-structured interviews were conducted with a sample of 14 adolescent boys (ranging in age from 10-12 years) who were randomly selected from the participant pool of a larger quantitative study (N=167) conducted in elementary schools in Berlin, Germany. By using thematic analyses, two major themes were identified: (1) social comparison (including two subthemes: self-improvement and self-enhancement), and (2) internalization (including two subthemes: behavioral and cognitive dimensions). On the basis of these results, a final model of how boys conceptualize body image in early adolescence was elucidated, and can be found in the study." (author's abrstact

The Big-Fish-Little-Pond Effect on the Four Facets of Academic Self-Concept

The social context plays a decisive role in the formation of the academic self-concept (ASC) and has been widely studied as the big-fish-little-pond-effect (BFLPE). This effect describes that comparable talented students in high-achieving school settings have a lower ASC compared to equally talented students attending low-achieving settings. Past research has focused on students’ domain-specific ASC, while little is known about the relation of achievement-related classroom compositions and the various facets of ASC. Additionally, BFLPE-research has been critiqued to build its theoretical frame on social comparison theory, without providing sufficient empirical support. To address this gap, we analyzed how the single student’s social, criterial, absolute, and individual ASC relate to class-level achievement of 8th graders. Applying Multilevel Structural Equation Modeling (MLSEM) we found that all facets of ASC were significantly related to average-class achievement, while student’s social ASC revealed the strongest associated. The results reveal explicitly that average-class achievement is strongly related to social comparison processes

The interplay between perceived stress and socio-emotional and behavioural factors during adolescence

Der erste Teil dieser Arbeit umfasst empirische Befunde und theoretische Grundlagen zu Stress in seiner historischen Entwicklungsgeschichte und sozio-emotionalen und behavioralen Faktoren. Die erste Studie dieser Dissertation fokussiert die Beziehung zwischen erlebtem Stress im Jugendalter, den Kontextvariablen der erlebten Hilfsbereitschaft und erlebtem Konkurrenzerleben und sozio-emotionale und behaviorale Stärken und Schwächen (d.h. emotionale Probleme, Symptome der Hyperaktivität, Probleme mit Peers, prosoziales Verhalten und problematische Verhaltensweisen) im Verlauf der Adoleszenz. Es wurde eine mögliche Moderation oder Mediation des Effektes von erlebtem Stress auf sozio-emotionale und behaviorale Stäken und Schwächen durch die beiden Kontextvariablen postuliert. Die Prüfung der Hypothesen erfolgte mittels latent moderierendem Strukturgleichungsmodell (Moderationsanalyse) und Multigruppen-Strukturgleichungsmodell unter Berücksichtigung des Geschlechts und Alters (Mediationsanalyse) der Schülerinnen und Schüler. Theoretische Grundlage ist das transaktionale Stressmodell nach Lazarus und Folkman (1984). Die zweite Studie dieser Dissertation widmet sich der Frage ob erlebter Stress ein möglicher Moderator in der Beziehung zwischen depressiven Symptomen in der frühen und sozio-emotionale und behaviorale Stärken und Schwächen in der mittleren Adoleszenz darstellt. Auf Basis der cognitive vulnerability-transactional stress theory von Hankin und Abramson (2001), die von reziproken und dynamischen Beziehungen zwischen Individuum und Umwelt ausgeht, wurde der Frage nachgegangen und die Beziehungen mittels latent moderierendem Strukturgleichungsmodell getestet. Die dritte Studie dieser Dissertation basiert auf dem Sozio-Ökologischen Modell nach Bronfenbrenner (1975). Darin wurde anhand eines Cross-Lagged-Panel Designs die Beziehungen zwischen Variablen emotionaler (In-)Stabilität (depressive Symptome, erlebter Stress und Einsamkeitserleben) und sozio-ökologischen Faktoren (Zugehörigkeitsgefühl, Beziehung zwischen Schüler/-Innen und Schüler/-Innen und Lehrer/Innen) innerhalb der Messzeitpunkte und im Laufe der Adoleszenz untersucht. Am Ende der Arbeit findet sich eine Zusammenfassung alle Ergebnisse, eine Diskussion und ein Ausblick für zukünftige Forschungsarbeiten.The first part of my work comprises empirical findings and theoretical foundations on stress in its historical development and socio-emotional and behavioural factors. The first study of my dissertation focuses on the relationship between perceived stress in adolescence, the context variables of perceived helpfulness and competition and socio-emotional and behavioural strengths and difficulties (i.e., emotional problems, symptoms of hyperactivity, problems with peers, prosocial behaviour and conduct problems) from early to middle adolescence. I postulated a moderation or mediation of the effect of perceived stress on socio-emotional and behavioural strengths and difficulties through the two context variables. My hypotheses were tested using a latent moderating structural equation model (moderation analysis) and a multi-group structural equation model taking into account the gender and age of the students (mediation analysis). The theoretical basis of my first study is the transactional stress model by Lazarus and Folkman (1984). The second study of my dissertation is dedicated to the question whether perceived stress is a moderator in the relationship between depressive symptoms in early adolescence and socio-emotional and behavioural strengths and difficulties in middle adolescence. Based on the cognitive vulnerability-transactional stress theory of Hankin and Abramson (2001), which assumes reciprocal and dynamic relationships between the individual and the environment, I investigated this question and tested the relationships using a latent moderating structural equation model. The third study of my dissertation is based on Bronfenbrenner’s socio-ecological model (1975). Using a cross-lagged panel design, I investigate the within time and longitudinal relationships between variables of emotional (in-)stability (i.e., depressive symptoms, perceived stress and loneliness) and socio-environmental factors (i.e., sense of belonging, student-student and teacher-student-relationship) from early to middle adolescence. At the end of my work there is a summary of all results, a discussion and an outlook for future research

Tracking Coordination Environment and Reaction Intermediates in Homo- and Heterogeneous Epoxidation Catalysts via Ti L2,3-edge NEXAFS

Ti-based molecules and materials are ubiquitous, and play a major role in both homogeneous and heterogeneous catalytic processes. Understanding the electronic structures of their active sites (oxidation state, local symmetry and ligand environment) is key to developing molecular-level structure-property relationships. In that context, X-ray absorption spectroscopy (XAS) offers a unique combination of element selectivity and sensitivity to local symmetry. Commonly, for early transition metals such as Ti, K-edge XAS is applied for in situ characterization and subsequent structural analysis with high sensitivity towards tetrahedral species. Ti L2,3-edge spectroscopy is in principle complementary and offers specific opportunities to interrogate the electronic structure of five-and six-coordinated species. It is, however, much more rarely implemented, because the use of soft X-rays implies ultra-high vacuum conditions. Furthermore, the interpretation of the data can be challenging. Here, we show how Ti L2,3-edge spectroscopy can help to obtain unique information about both homogenous and heterogeneous epoxidation catalysts and to develop a molecular-level relationship between spectroscopic signatures and electronic structures. Towards this goal, we first establish a spectral library of molecular Ti reference compounds, comprising various coordination environments with mono- and dimeric Ti species having O, N and Cl-ligands. We next implemented a computational methodology based on multiplet ligand field theory and maximally localized Wannier orbitals benchmarked on our library to understand Ti L2,3-edge spectroscopic signatures. We finally used this approach to track and predict spectra of catalytically relevant intermediates, focusing on Ti-based olefin epoxidation catalysts

Role and dynamics of transition metal carbides in methane coupling

Transition metal carbides have numerous applications and are known to excel in terms of hardness, thermal stability and conductivity. In particular, the Pt-like behavior of Mo and W carbides has led to the popularization of metal carbides in catalysis, ranging from electrochemically-driven reactions to thermal methane coupling. Herein, we show the active participation of carbidic carbon in the formation of C2 products during methane coupling at high temperature that is associated with the dynamics of Mo and W carbides. A detailed mechanistic study reveals that the catalyst performance of these metal carbides can be traced back to its carbon diffusivity and exchange capability upon interaction with methane (gas phase carbon). A stable C2 selectivity over time on stream for Mo carbide (Mo2C) can be rationalized by fast carbon diffusion dynamics, while W carbide (WC) shows loss of selectivity due to slow diffusion leading to surface carbon depletion. This finding showcases that the bulk carbidic carbon of the catalyst plays a crucial role and that the metal carbide is not only responsible for methyl radical formation. Overall, this study evidences the presence of a carbon equivalent to the Mars–Van Krevelen type mechanism for non-oxidative coupling of methane.ISSN:2041-6520ISSN:2041-653

Role and Dynamics of Transition Metal Carbides in Methane Coupling

Transition metal carbides have numerous applications and are known to excel in terms of hardness, thermal stability and conductivity. In particular, the Pt-like behavior of Mo and W carbides has led to a popularization of metal carbides in catalysis, ranging from electrochemically-driven reactions to thermal methane coupling. Herein, we show the dynamics of Mo and W carbides and the active participation of carbidic carbon in the formation of C2 products during methane coupling. A detailed mechanistic study reveals that the catalyst performance of these metal carbides can be traced back to its carbon diffusivity and exchange capability upon interaction with gas phase carbon (methane). A stable C2 selectivity over time on stream for Mo carbide (Mo2C) can be rationalized by fast carbon diffusion dynamics, while W carbide (WC) shows loss of selectivity due to slow diffusion leading to surface carbon depletion. This finding showcases that the bulk carbidic carbon of the catalyst plays a crucial role and that the metal carbide is not only responsible for methyl radical formation. Overall, this study supports the presence of a carbon equivalent to the Mars-Van Krevelen type mechanism for non-oxidative coupling of methane, thus introducing guiding principles to design and develop associated catalysts

Active Site Descriptors from 95Mo NMR Signatures of Silica-supported Mo-based Olefin Metathesis Catalysts

The catalytic activity of silica-supported molybdenum oxides for olefin metathesis depends strongly on the metal loading and preparation conditions indicating that the nature and/or amounts of the active sites vary across catalysts. This is illustrated by comparing Mo-based (pre)catalysts prepared by impregnation with different metal loadings (2.5-15.6 wt% Mo) and a well-defined model material (2.3 wt% Mo) prepared via a surface organometallic chemistry (SOMC) synthetic approach. Analyses of FTIR, UV-vis, and Mo K-edge X-ray absorption spectra provide strong evidence that all the (pre)catalysts are composed predominantly of similar isolated Mo dioxo sites; however, they exhibit very different proportions of reducible surface sites and catalytic reaction properties. Specifically, the SOMC-derived catalyst is more active for liquid and gas-phase olefin metathesis conditions than a classical catalyst of similar Mo loading by a factor of 1.5-1.9, depending on precise reaction conditions. Most notably, solid-state 95Mo NMR spectra of these catalysts show distinct features, particularly evident under state-of-the-art high-field (28.2 T) measurement conditions where at least four distinct types of surface Mo dioxo sites are resolved, the distribution of which depends on the preparation methods. In particular, the presence of Mo sites with a specific deshielded 95Mo NMR signal correlates with the catalysts reducibility and metathesis activity; such sites are most prominent in the SOMC-derived catalyst. First-principles calculations show that the 95Mo NMR parameters, specifically the isotropic chemical shift and quadrupolar coupling constant, are good descriptors for local strain and coordination environment: acute (SiO-Mo(O)2-OSi) angles and low coordination numbers at the Mo sites leads to highly deshielded iso chemical shifts and small CQ values, respectively. Orbital and natural chemical shift analyses indicate that the deshielded 95Mo iso values of strained species are directly related to low LUMO energies, consistent with their higher reducibility and corresponding reactivity. Overall, this study shows that solid-state NMR is particularly powerful for the identification of distinct supported Mo dioxo species and that their 95Mo chemical shifts are related to their specific local electronic structures, providing a powerful descriptor for the propensity of Mo sites towards reduction and the formation of active sites

NMR Signatures and Electronic Structures of Ti-sites in Titanosilicalite-1 from solid-state 47/49Ti NMR Spectroscopy

Although titanosilicalite-1 (TS-1) is among the most successful oxidation catalysts used in industry, its active site structure is still debated. Recent efforts have mostly focused on understanding the role of defect sites and extra-framework Ti. Insights into the positions and distributions of framework tetrahedral Ti sites remain scarce, in part due to the lack of direct characterization techniques with sufficient sensitivity. Here, we report the 47/49Ti solid-state NMR characterization of TS-1 and its molecular models, [Ti(OTBOS)4] and [Ti(OTBOS)3(OiPr)]. Analysis of their spectroscopic signatures, augmented by computational studies, shows pronounced differences that originate from specific arrangements of the second coordination sphere of Ti atoms, yielding information on titanium siting in TS-1

Active Site Descriptors from 95Mo NMR Signatures of Silica-Supported Mo-Based Olefin Metathesis Catalysts

The olefin metathesis activity of silica-supported molybdenum oxides depends strongly on metal loading and preparation conditions, indicating that the nature and/or amounts of the active sites vary across compositionally similar catalysts. This is illustrated by comparing Mo-based (pre)catalysts prepared by impregnation (2.5–15.6 wt % Mo) and a model material (2.3 wt % Mo) synthesized via surface organometallic chemistry (SOMC). Analyses of FTIR, UV–vis, and Mo K-edge X-ray absorption spectra show that these (pre)catalysts are composed predominantly of similar isolated Mo dioxo sites. However, they exhibit different reaction properties in both liquid and gas-phase olefin metathesis with the SOMC-derived catalyst outperforming a classical catalyst of a similar Mo loading by ×1.5–2.0. Notably, solid-state 95Mo NMR analyses leveraging state-of-the-art high-field (28.2 T) measurement conditions resolve four distinct surface Mo dioxo sites with distributions that depend on the (pre)catalyst preparation methods. The intensity of a specific deshielded 95Mo NMR signal, which is most prominent in the SOMC-derived catalyst, is linked to reducibility and catalytic activity. First-principles calculations show that 95Mo NMR parameters directly manifest the local strain and coordination environment: acute (SiO–Mo(O)2–OSi) angles and low coordination numbers at Mo lead to highly deshielded 95Mo chemical shifts and small quadrupolar coupling constants, respectively. Natural chemical shift analyses relate the 95Mo NMR signature of strained species to low LUMO energies, which is consistent with their high reducibility and corresponding reactivity. The 95Mo chemical shifts of supported Mo dioxo sites are thus linked to their specific electronic structures, providing a powerful descriptor for their propensity toward reduction and formation of active sites.ISSN:0002-7863ISSN:1520-512