Wear Behavior of Uncoated and Coated Tools under Complex Loading Conditions

In automotive industry crash relevant structures of the body in white are manufactured using the direct hot stamping process. Due to the high temperature difference between the hot blank and the cold tool surfaces and the relative movement between the blank and the tool surfaces during the forming operation, high thermal and mechanical loads are applied on the tool leading to excessive wear in terms of adhesion on the tool surfaces. One possibility to reduce wear of hot stamping tools is the application of tool coating systems. In the scope of this work uncoated and coated tools are characterized under complex loading conditions with respect to adhesive layer build-up

The East End, the West End, and King's Cross: On Clustering in the Four-Player Hotelling Game

We study experimentally a standard four-player Hotelling game, with a uniform density of consumers and inelastic demand. The pure strategy Nash equilibrium configuration consists of two firms located at one quarter of the ``linear city'', and the other two at three quarters. We do not observe convergence to such an equilibrium. In our experimental data we find three clusters. Besides the direct proximity of the two equilibrium locations this concerns the focal mid-point. Moreover, we observe that whereas this mid-point appears to become more notable over time, other focal points fade away. We explain how these observations are related to best-response dynamics, and to the fact that the players rely on best-responses in particular when they are close to the equilibrium configuration.Location model, Nonconvergence, Focal point, Best-response dynamics

Bringing College Classes to High School

Recent education reforms have focused heavily on increasing academic rigor for secondary students attending public schools with a goal of improved academic outcomes for all students. A common practice for increasing rigor school-wide is the adoption of college-level curriculums such as dual-credit, Advanced Placement, and the International Baccalaureate in U.S public secondary schools. This study examined the relationship between the implementation of one or more college-level curriculum(s) in a public secondary school and overall student academic achievement. Academic achievement was measured by student performance on the Washington state standardized End of Course exam in Biology and the Smarter Balanced exams in English Language Arts and Mathematics, while controlling for demographic difference between schools (N = 559). Additionally, this study examined the relationship between the implementation of a college-level curriculum and on-time graduation rates for the class of 2015, also controlling for demographic differences between schools (N = 559). A generalized linear mixed model was utilized to examine school-level exam data and demographic data from the Washington state Office of Superintendent of Public Instruction for the 2014-2015 academic year to assess whether the presence of a college-level curriculum in a secondary school setting influenced academic achievement and on-time graduation. Results of the GLMMs suggested that the presence of a college-level curriculum in the school does increases the odds of passing the EOC Biology exam but does not increase the odds of passing the SBA ELA exam or passing the SBA Math exam. Results of the GLMMs suggested that the presence of a college-level curriculum in the school also increases the odds of graduating on time

Predicting Procrastination in Everyday Life - From Individual Differences in Procrastination Tendencies to Intraindividual Variability in Momentary Task Appraisal

Procrastination is typically defined as an irrational behavior characterized by unnecessarily delaying the completion of important tasks, contrary to one’s original intention, despite knowing that doing so could be to one’s detriment (cf. Klingsieck, 2013; Simpson & Pychyl, 2009; Steel, 2007). Taking a trait-based perspective, research has consistently shown that students’ self-reported procrastination tendencies are closely related to individual differences in conscientiousness, neuroticism, or impulsivity (Ferrari & Emmons, 1995; Lee et al., 2006; Schouwenburg & Lay, 1995; Watson, 2001). At the same time, procrastination can be understood as a task-specific avoidance behavior resulting from a failure of self-regulation (DeWitte & Lens, 2000; Howell et al., 2006; Steel et al., 2018). An effort to understand the occurrence of procrastination behavior as a failure of self-regulation would require to consider that individuals’ self-regulatory capacities — their motivational and volitional determinants — may change over time depending on task- or context-specific influences (see Dietrich et al., 2017; Martin et al., 2015; Vancouver & Kendall, 2006; Wäschle et al., 2014). Accordingly, research that seeks to identify the conditions that result in a failure to act in line with one’s intentions (i.e., the conditions that lead to the occurrence of an intention-action gap; Sheeran & Webb, 2016) will need to go beyond the examination of individual differences in procrastination tendencies. Accounting for individual differences in students’ procrastination behavior that can be attributed to trait-based determinants, the primary purpose of the present dissertation was to determine intra-individual mechanisms that affect the actual occurrence of procrastination behavior in real-life academic situations. To capture momentary changes (i.e., within-person changes) in motivational and volitional determinants that precede the occurrence of procrastination behavior, an event-based experience sampling approach was developed and implemented in a total of three studies. Study 1 (Chapter 2) set out to examine whether the occurrence of behavioral delays (the occurrence of an intention-action gap) would be predicted by withinperson changes in students’ cognitive-affective appraisals of tasks that arise between successive stages of goal-directed action. For one week, N = 75 students used an electronic diary (e-diary) to indicate their intentions to work on academic tasks (582 tasks planned) and their task-related appraisals (expectation to realize their intention, task value, and task aversiveness, and the effort required) each evening. For each intended task, a second assessment requested the next day determined whether students’ task-related appraisals changed, and whether they realized their intention on time or delayed working on the task (21.2% delays based on 501 completed task-specific measurements). Stepwise two-level logistic regression analyses revealed that lower expectations of success (i.e., ratings falling below an individual’s average) predicted an increased probability for task-specific delays. The risk that a task was delayed increased significantly when within-person changes in students’ appraisals indicated a devaluation (i.e., decreases in task-value, and increases in taskaversiveness). Students’ general procrastination tendencies that have been assessed at baseline have not significantly contributed to explain their individual delay behavior. To more accurately determine whether the occurrence of a behavioral delay should to be interpreted as procrastination behavior, a new 5-item short scale (the ecological Momentary Assessment of Procrastination Scale, e-MAPS) was developed and tested for its psychometric properties in Study 2 (Chapter 3). The applicability of the e-MAPS was tested in an experience sampling study with N = 80 students who were instructed to schedule at least two tasks they intended to work on for each of 17 days. At the time they intended to realize their intentions (2651 tasks planned), students were asked whether they worked on their task, or delayed working contrary to their original intention. If they had delayed working on their task (231 delays reported by 65 participants), participants were asked to complete the e-MAPS. An exploratory factor analysis revealed that the e-MAPS items covered two latent components, supporting the preconception that both situational and cognitive-affective determinants were relevant to classify a delay as procrastination behavior (25.5% of the delays classified as procrastination). A confirmatory factor analysis indicated that individual differences in delay patterns were assessed reliably. Associations between individuals’ aggregate frequencies of procrastination behavior captured by the e-MAPS, and their procrastination tendencies captured at baseline using two established self-report scales, support the convergent validity of the new scale. Study 3 (Chapter 4) extended the findings presented in Study 1 using the eMAPS to examine the influence that students’ perceptions of task-related ambiguity (i.e., uncertainty about actions or means required to successfully accomplish a task) had on the occurrence of procrastination behavior in studying for an exam. Questionnaires assessing students’ (N = 88) procrastination tendency and conscientiousness at baseline were combined with an adaptive experience sampling approach to assess students’ task-related perceptions of ambiguity and their situation-specific procrastination behavior during exam preparation six times a day for seven days (3581 measurements completed). Results revealed that 30% of 2286 intended study sessions were procrastinated. Study sessions were significantly more likely to be procrastinated when the momentary task-related ambiguity perception exceeded an individual’s average ambiguity perception (i.e., averaged across all intended study sessions). Students with pronounced procrastination tendencies were more likely, while more conscientious students were less likely to procrastinate study sessions. However, students’ conscientiousness explained virtually no variance in their procrastination behavior that was not explained by their general procrastination tendency. There was no indication for individual differences in the effect of ambiguity perceptions on the risk for procrastinating study sessions that could have been explained by students’ general procrastination tendency or conscientiousness. Two main conclusions can be drawn from the studies presented: First, it seems pertinent to consider trait-based determinants and more task- or contextspecific fluctuations in students’ self-regulatory capacities as complementary in their influence on the occurrence of procrastination behavior. Second, our findings highlight the ongoing imperative to examine procrastination behavior not only in terms of a general trait-based behavioral tendency, but also as a behavior that unfolds over time. Moreover, the latter requires to account for the fact that not every delay of an intended action should be considered an instance of procrastination. The use of trait- and state-based measurement approaches represents a major strength of the studies included in this dissertation. The implementation of an innovative experience sampling approach provided insights into the temporal instability of students’ intentions to initiate taskrelated actions, thus extending the available knowledge about intra-individual mechanisms that contribute to the occurrence of procrastination behavior. Further implications for research and practice will be discussed (Chapter 5)

AC electric trapping of neutral atoms

We study the dynamic behavior of ultracold neutral atoms in a macroscopic ac electric trap. Confinement in such a trap is achieved by switching between two saddle-point configurations of the electric field. The gradual formation of a stably trapped cloud is observed and the trap performance is studied versus the switching frequency and the symmetry of the switching cycle. Additionally, the electric field in the trap is mapped out by imaging the atom cloud while the fields are still on. Finally, the phase-space acceptance of the trap is probed by introducing a modified switching cycle. The experimental results are reproduced using full three-dimensional trajectory calculations.Comment: 10 pages, 13 figures, updated version, added journal referenc

Covariant boost and structure functions of baryons in Gross-Neveu models

Baryons in the large N limit of two-dimensional Gross-Neveu models are reconsidered. The time-dependent Dirac-Hartree-Fock approach is used to boost a baryon to any inertial frame and shown to yield the covariant energy-momentum relation. Momentum distributions are computed exactly in arbitrary frames and used to interpolate between the rest frame and the infinite momentum frame, where they are related to structure functions. Effects from the Dirac sea depend sensitively on the occupation fraction of the valence level and the bare fermion mass and do not vanish at infinite momentum. In the case of the kink baryon, they even lead to divergent quark and antiquark structure functions at x=0.Comment: 13 pages, 12 figures; v2: minor correction