President Park Jeong-hui had promoted "The Saemaul Movement" in early 1970s to improve people's life, and straw-thatched roofs in agricultural villages were displaced by asbestos containing slates, which have resulted in scattering hazardous materials. The Korean government has determined to enact the asbestos safety law from 2012 and established Korea Research Center of Asbestos-Related Diseases in Pusan National University in advance. The paper reviews and proposes detoxification and recycling of waste asbestos-containing building materials based on technical state of Korea and Japan, where development of an on-site transferable plant is suggested to be effective.
The aim of this study was to fabricate deformable chitosan (CS) microspheres for arterial embolization. CS microspheres containing poly(ethylene glycol) (PEG) were prepared by ionotropic gelation; PEG was then removed from the CS microspheres to produce the highly porous structure to allow deformability. The porosity was controlled by blending ratios of CS/PEG polymers (CS/PEG=from 100/0 to 15/85) and the effect of porosity on microcatheter delivery was examined. The size range of porous microspheres was 500—600 μm with sphericity between 1.012—1.041. Scanning electron microscope observation confirmed that microporous networks were effectively obtained by PEG extraction proportional to the initial amount of PEG. Water retention capacities, indicative of internal porosities of microspheres, increased with increasing initial amounts of blended PEG. CS microspheres with water retention values of greater than 28% exhibited noticeable deformation and smooth passage through the microcatheter tip. Novel deformable microspheres are, therefore, expected to be clinically applicable for arterial embolization.
This paper deals with the grinding characteristics of a target type fluid-energy mill, in which flying particles are ground by repeated impact on a target. The increase of specific surface area ΔSw and the distribution of particle size were investigated with respect to the following parameters: the target distance from nozzle outlet to target surface L, the target angle between air flow axis and target surface, the mixing ratio m of particles to air by weight, and the initial air pressure. It was found that there were optimum L and m values for grinding, estimated to be 70±10 mm for L and 0.7-1.0 for m over almost all the experimental range. The energy efficiency ΔSw/Ef, defined as ΔSw per energy Ef in adiabatic expansion of air, was proportional to 1.0-1.2 power of m to m=0.7. On the other hand, the input energy per unit products was inversely proportional to the particle size of products in the region of fine particle size, while it was independent of the particle size of products in the region of large particle size.
The mechanism of cutting fracture of a polypropylene (PP) is investigated by an experimental approach in which a PP particle accelerated by an axially symmetrical nozzle collides repeatedly with a wedge-shaped target. This experimental approach is useful in comminuting a polymeric material having viscoelastic properties such as those of PP. The mechanism of impact cutting fracture is examined mainly on the basis of the relation between the increase of specific surface area, the cutting probability, and the cumulative specific kinetic energy of the particle. The increase of specific surface area can be formulated by a power law in terms of the product of the cutting probability and the cumulative specific energy, and the value of its exponent is estimated to be 0.8 within this experimental range.
Various memristor-based synaptic devices have been proposed for implementing a neuromorphic system. However, memristor devices typically suffer from various inherent problems such as nonlinearity and asymmetry of conductance modulation and the sneak path issue of the crossbar array structure. To solve these drawbacks, we propose a one transistor–two memristor (1T2M) synaptic device, its array structure, and its operation method for neuromorphic system applications. For the channel of the transistor and switching layer of the memristor, amorphous InGaZnO was used. The proposed 1T2M synaptic device exhibited more linear and symmetric characteristics of conductance modulation compared with the single memristor device. In addition, the proposed array structure was robust to the sneak path problem. To investigate the switching mechanism, a depth profile analysis of X-ray photoelectron spectroscopy was conducted for each resistance state. Finally, we confirmed an excellent pattern recognition accuracy by using an artificial neural network simulation.
In this work, flexible InGaZnO (IGZO) synaptic thin-film transistors (TFTs) with different gate dielectric layers are fabricated and analyzed to investigate the effect of the gate insulator of flexible IGZO synaptic TFTs in terms of weight window and retention characteristics. The gradual weight modulation of these devices comes from the migration of hydrogens in the Al2O3 layer deposited by low-temperature atomic layer deposition and can be controlled by gate bias. In addition, the learning behaviors with identical and incremental pulse schemes are verified for a linear weight modulation, and its effect in pattern recognition accuracy is studied considering device variation and retention properties in a 784 × 10 fully connected neural network with handwritten digit images.
As trap-related conduction is crucial in achieving ovonic threshold switching characteristics, identifying the distribution of traps in the chalcogenide matrix is essential. Herein, the density of states (DOS) near the valence band maximum level (EV) and conduction band minimum level (EC) of GeSe layers extracted using various electrical methodologies were analyzed. When electrons in the GeSe layer participate in activation under light injection, the DOS distribution at EV can be calculated. On the other hand, capacitance measurement with respect to frequencies allows the identification of the lowest energy levels of EC containing electrons that can respond to the provided AC signals. When an As dopant is introduced into the GeSe layer, the unified DOS distribution indicates a decrease in the Se element concentration owing to the over-coordinated Ge state. Therefore, increased DOS at EC is observed, which is in good agreement with the ab initio explanation. Additional simulations were performed considering plausible scenarios in which the variation in DOS profile depends on the parameters of the transport mechanism. These results reveal the ways in which threshold switching can be controlled and facilitate the understanding of electrically achieved behavior.
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