Molecular-dynamics study of multi-pulsed ultrafast laser interaction with copper

Ultrafast laser has an undeniable advantage in laser processing due to its extremely small pulse width and high peak energy. While the interaction of ultrafast laser and solid materials is an extremely non-equilibrium process in which the material undergoes phase transformation and even ablation in an extremely short time range. This is the coupling of the thermos elastic effect caused by the pressure wave and the superheated melting of the material lattice. To further explore the mechanism of the action of ultrafast laser and metal materials, the two-temperature model coupling with molecular dynamics method was used to simulate the interaction of the copper and laser energy. Firstly, the interaction of single-pulsed laser and copper film was reproduced, and the calculated two-temperature curve and the visualized atomic snapshots were used to investigate the influence of laser parameters on the ablation result. Then, by changing the size of the atomic system, the curve of ablation depth as a function of laser fluence was obtained. In this paper, the interaction of multi-pulsed laser and copper was calculated. Two-temperature curve and temperature contour of copper film after the irradiation of double-pulsed and multi-pulsed laser were obtained. And the factors which can make a difference to the incubation effect were analyzed. By calculating the ablation depth under the action of multi-pulsed laser, the influence of the incubation effect on ablation results was further explored. Finally, a more accurate numerical model of laser machining metal is established and verified by an ultra-short laser processing experiment, which provides a new calculation method and theoretical basis for ultra-fast laser machining of air film holes in aviation turbine blades, and has certain practical guiding significance for laser machining.

The incubation effect among students playing an educational game for physics

The incubation effect (IE) is a problem-solving phenomenon composed of three phases: pre-incubation where one fails to solve a problem; incubation, a momentary break where time is spent away from the unsolved problem; and post-incubation where the unsolved problem is revisited and solved. Literature on IE was limited to experiments involving traditional classroom activities. This initial investigation showed evidence of IE instances in a computer-based learning environment. This paper consolidates the studies on IE among students playing an educational game called Physics Playground and presents further analysis to examine the incidence of post-incubation or the revisit to a previously unsolved problem. Prior work, which focused on predicting successful outcomes, includes a coarse-grained IE model developed with logistic regression on aggregated data and an improved model which leveraged long short-term memory (LSTM) combined with dimensionality reduction visualization technique and clustering on fine-grained data. The additional analysis which aims to understand factors that may trigger the post-incubation phase also used fine-grained data and LSTM to create a revisit model. Results show that time elapsed relative to the activity period and encountering a problem with a similar solution during incubation were possible factors in revisiting previously unsolved problems.

Do We Need to Forget Fixations to Incubate? A Paradox of the Forgetting Fixation Theory

The incubation period is regarded as an important stage in creative problem solving. The incubation effect manifests itself in the enhanced problem-solving performance after taking a break. Forgetting fixation hypothesis states that incubation provides a problem solver with an opportunity to eliminate inappropriate ideas (mental sets) and therefore to come up with a correct solution. We explored in two studies whether forgetting is an actual mechanism of the incubation period (i.e. whether the traces of inappropriate fixations in memory become weaker as a consequence of incubation). In Study 1 we employed the Alternative Uses Task (AUT) and fixed part of the participants on several most common ways of using an object. We checked then whether incubation helped to forget our fixations. We found the incubation effect (i.e. a greater fluency at the second attempt) only when participants were previously fixated. However, we also found that the incubation didn’t influence the number of fixations. Thus, we failed to find the evidence for forgetting fixation during the incubation period. In Study 2 we used anagrams with two possible solutions and fixed the participant on one of them. Then we used the Lexical Decision Task (LDT) to examine whether these fixations would become weaker as a result of the incubation period. No differences were found between the incubation and no-incubation groups in their response latencies for fixation words. Our results indicate that while the assumption that the function of an incubation period is in overcoming inappropriate mental sets seems to be true, the forgetting fixation theory provides an inaccurate account of underlying mechanisms.

Incubation Research: Potential of Within Subject and Between Subject Experimental Design

In the current work we aimed to detect the incubation effect using between-subject and within-subject design. We compared the performance rate of solving Remote Association Test in incubation (with a break) and no-incubation conditions. During the incubation phase participants were listening to the audio record of the science-fiction novel. No significant differences were found in the performance level in incubation and no-incubation conditions, neither in within-group nor in the between-group tests. Nonetheless we found the indirect indicators of the processes that are encountered during the incubation period. The discrepancy in the absence of raw performance indicators of incubation on the one hand, and the presence of the difficulty indicators changes on another hand, is discussed in the context of the activation paradigm and the model of awareness of implicit solution.