Size-Tunable Semiconducting 2D Nanorectangles from Conjugated Polyenyne Homopolymer Synthesized via Cascade Metathesis and Metallotropy Polymerization.

Size-tunable semiconducting two-dimensional (2D) nanosheets from conjugated homopolymers are promising materials for easy access to optoelectronic applications, but it has been challenging due to the low solubility of conjugated homopolymers. Herein, we report size-tunable and uniform semiconducting 2D nanorectangles via living crystallization-driven self-assembly (CDSA) of a fully conjugated polyenyne homopolymer prepared by cascade metathesis and metallotropy (M&M) polymerization. The resulting polyenyne with enhanced solubility successfully underwent living CDSA via biaxial growth mechanism, thereby producing 2D nanorectangles with sizes precisely tuned from 0.1 to 3.0 µm2 with narrow dispersity mostly less than 1.1 and low aspect ratios less than 3.1. Furthermore, living CDSA produced complex 2D block comicelles with different heights from various degrees of polymerization (DPs) of unimers. Based on diffraction analyses and DFT calculations, we proposed an interdigitating packing model with an orthorhombic crystal lattice of semiconducting 2D nanorectangles.

Risk Assessment of Tractor-Related Hazards Based on Accident Cases.

Annually, tractor accidents are estimated to account for more than 100 deaths in South Korea. Periodic accident surveys have served as an essential means for the National Institute of Agricultural Sciences (NAS) to develop strategies to prevent tractor accidents. In this study, hazards leading to accidents were identified, and their risks were assessed based on survey results to establish a more effective accident prevention strategy. Risk assessment for hazards proceeded as follows: hazard identification, frequency estimation, number of equivalent fatalities (NEF) estimation, and finally risk evaluation. Hazards were identified by analyzing 588 accident cases from NAS surveys and performing an expert review of the analysis results by implementing a Delphi survey. The frequency and NEF of each hazard were estimated by multiplying its probabilities and the statistical results of the NAS surveys. Each hazard was plotted in a frequency-NEF (FN) diagram and evaluated according to its position. Fifty-four hazards were identified, and their frequencies and NEF values were estimated. The risk evaluation results, based on the FN diagram, revealed that no hazard was located in the "unacceptable" area, and two hazards (carelessness and not looking ahead carefully) were in the "as low as reasonably practicable" area. Thus, it is critical to mitigate the effects of these two hazards. With the risk assessment method used in this study, personnel who are engaged in the prevention of tractor accidents, such as policymakers, extension specialists, and researchers, can quantitatively predict how many cases or fatalities can be reduced by eliminating a certain hazard.