Flaw tolerance promoted by dissipative deformation mechanisms between material building blocks

Novel high-performance composite materials often draw inspiration from natural materials such as bone or mollusc shells. A prime feature of such composites is that they are, like their natural counterparts, quasibrittle. They are tolerant to material flaws up to a certain characteristic flaw-tolerant size scale, exhibiting high strength and toughness, but start to behave in a brittle manner when sufficiently large flaws are present. Here, we establish that better flaw tolerance can be achieved by maximizing fracture toughness relative to the maximum elastic energy available in the material, and we demonstrate this concept with simple two-dimensional coarse-grained simulations where the transition from brittle to quasibrittle behaviour is examined.     

Phase-field crystal modeling of anisotropic material systems of arbitrary Poisson's ratio

Recently, we derived a generalized model for isotropic as well as anisotropic crystal lattice systems of arbitrary Poisson's ratio within the framework of the continuum phase-field crystal (PFC) approach [R. Prieler, J. Hubert, D. Li, B. Verleye, R. Haberkern, H. Emmerich, J. Phys.: Condens. Matter 21 (2009) p.464110] and showed how its parameters can be derived from classical density functional theory [M.A. Choudhary, D. Li, H. Emmerich and H. Löwen, J. Phys.: Condens. Matter 23 (2011) p.265005]. Here, we present a general procedure to model anisotropic material systems of arbitrary Poisson's ratios. In that way we can for the first time identify PFC solutions of arbitrary Poisson's ratios and thereby extend the applicability of the PFC method to a larger class of material systems.     

Scaling relationships in indentation of power-law creep solids using self-similar indenters

We use dimensional analysis to derive scaling relationships for self-similar indenters indenting solids that exhibit power-law creep. We identify the parameter that represents the indentation strain rate. The scaling relationships are applied to several types of indentation creep experiment with constant displacement rate, constant loading rate or constant ratio of loading rate over load. The predictions compare favourably with experimental observations reported in the literature. Finally, a connection is found between creep and 'indentation-size effect' (i.e. changing hardness with indentation depth or load).     

Many-body potential for nitrogen in α-iron

N atom is one of the most frequent foreign interstitial atoms in α-iron along with C atoms. The Fe–C potential has been well-developed and can reproduce many significant interactions of C with point defects present in α-iron. However, there exists no satisfactory Fe–N potential to describe the interactions of N with point defects. Here, we develop a many-body potential for N in α-iron. The potential parameters are determined by fitting to ab initio data, which includes energetics, configurations, and relaxations of Fe atoms close to N atom. This potential successfully describes the interactions of Fe–N across a wide range of defect environments. The potential employs the embedded atom method form and hence is appropriate for large-scale molecular dynamics simulation.     

校正的Bootstrap方法对概化理论方差分量及其变异量估计的改善

Bootstrap方法是一种有放回的再抽样方法, 可用于概化理论的方差分量及其变异量估计。用Monte Carlo技术模拟四种分布数据, 分别是正态分布、二项分布、多项分布和偏态分布数据。基于p×i设计, 探讨校正的Bootstrap方法相对于未校正的Bootstrap方法, 是否改善了概化理论估计四种模拟分布数据的方差分量及其变异量。结果表明：跨越四种分布数据, 从整体到局部, 不论是“点估计”还是“变异量”估计, 校正的Bootstrap方法都要优于未校正的Bootstrap方法, 校正的Bootstrap方法改善了概化理论方差分量及其变异量估计。     

The antecedents of anticipatory purchase: Reconciling the two routes to optimism

Consumers often behave optimistically, purchasing products that they are unable to use at the time of purchase, but anticipate being able to use in the future. This research investigates such anticipatory purchase behavior, and demonstrates that optimism exerts its influence on anticipatory purchase via two distinct routes. One is driven by the perceived ease of the process required to achieve a given outcome and prevails when sufficient cognitive resources are available, while the other is driven directly by the perceived favorability of the outcome itself and holds when cognitive resources are constrained. Within each route, the focus of thought (process vs. outcome-focus) moderates the influence of optimism, and the two routes converge on enhanced motivation. Multiple experiments provide support for predictions derived from this framework, illuminating the substantive domain of anticipatory purchasing and providing theoretical insights into the nature of optimism.     

How Do Propensity Score Methods Measure Up in the Presence of Measurement Error? A Monte Carlo Study

Considering that the absence of measurement error in research is a rare phenomenon and its effects can be dramatic, we examine the impact of measurement error on propensity score (PS) analysis used to minimize selection bias in behavioral and social observational studies. A Monte Carlo study was conducted to explore the effects of measurement error on the treatment effect and balance estimates in PS analysis across seven different PS conditioning methods. In general, the results indicate that even low levels of measurement error in the covariates lead to substantial bias in estimates of treatment effects and concomitant reduction in confidence interval coverage across all methods of conditioning on the PS.     

When far becomes near: Shared environments activate action simulation

It has been proposed that one means of understanding a person's current behaviour and predicting future actions is by simulating their actions. That is, when another person's actions are observed, similar motor processes are activated in the observer. For example, after observing a reach over an obstacle, a person's subsequent reach trajectory is more curved, reflecting motor priming. Importantly, such motor states are only activated if the observed action is in near (peripersonal) space. However, we demonstrate that when individuals share action environments, simulation of another person's obstacle avoiding reach path takes place even when the action is in far (extrapersonal) space. We propose that action simulation is influenced by factors such as ownership. When an “owned” object is a potential future obstacle, even when it is viewed beyond current action space, simulations are evoked, and these leave a more stable memory capable of influencing future behaviour.     

Comparing the neural correlates of affective and cognitive theory of mind using fMRI: Involvement of the basal ganglia in affective theory of mind

Theory of Mind (ToM) is the ability to infer other people’s mental states like intentions or desires. ToM can be differentiated into affective (i.e., recognizing the feelings of another person) and cognitive (i.e., inferring the mental state of the counterpart) subcomponents. Recently, subcortical structures such as the basal ganglia (BG) have also been ascribed to the multifaceted concept ToM and most BG disorders have been reported to elicit ToM deficits. In order to assess both the correlates of affective and cognitive ToM as well as involvement of the basal ganglia, 30 healthy participants underwent event-related fMRI scanning, neuropsychological testing, and filled in questionnaires concerning different aspects of ToM and empathy. Directly contrasting affective (aff) as well as cognitive (cog) ToM to the control (phy) condition, activation was found in classical ToM regions, namely parts of the temporal lobe including the superior temporal sulcus, the supplementary motor area, and parietal structures in the right hemisphere. The contrast aff > phy yielded additional activation in the orbitofrontal cortex on the right and the cingulate cortex, the precentral and inferior frontal gyrus and the cerebellum on the left. The right BG were recruited in this contrast as well. The direct contrast aff > cog showed activation in the temporoparietal junction and the cingulate cortex on the right as well as in the left supplementary motor area. The reverse contrast cog > aff however did not yield any significant clusters. In summary, affective and cognitive ToM partly share neural correlates but can also be differentiated anatomically. Furthermore, the BG are involved in affective ToM and thus their contribution is discussed as possibly providing a motor component of simulation processes, particularly in affective ToM.     

Cognitive determinants of the success of inventors: Complex problem solving and deliberate use of divergent and convergent thinking

With reference to Henderson's (2004) assumption that inventors are “expert problem solvers”, we studied the ability of inventors to solve complex problems (CPS) using a sample of 46 German inventors. The participants had to use FSYS 2.0, a computer-simulated microworld. Additionally, we assessed metacognition, in particular the participants' ability to make deliberate use of divergent and convergent thinking. This ability was expected to be an important skill involved in solving complex problems (Dörner, Kreuzig, Reither, & Stäudel, 1983). We assumed a positive correlation between the individual success of inventors (number of granted and marketed patents) and CPS abilities. Controllability of divergent and convergent thinking turned out to be a predictor of the success of inventors and allowed us to identify the top 10% performers. Oddly however, the best problem solvers were inventors with exactly one granted patent. Data from a posteriori conducted interviews help explaining the results.