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We demonstrated analog memory, synaptic plasticity, and a spike-timing-dependent plasticity (STDP) function with a nanoscale titanium oxide bilayer resistive switching device with a simple fabrication process and good yield uniformity. We confirmed the multilevel conductance and analog memory characteristics as well as the uniformity and separated states for the accuracy of conductance change. Finally, STDP and a biological triple model were analyzed to demonstrate the potential of titanium oxide bilayer resistive switching device as synapses in neuromorphic devices. By developing a simple resistive switching device that can emulate a synaptic function, the unique characteristics of synapses in the brain, e.g. combined memory and computing in one synapse and adaptation to the outside environment, were successfully demonstrated in a solid state device.

Feasibility of a high speed pattern recognition system using 1k-bit cross-point synaptic RRAM array and CMOSbased neuron chip has been experimentally demonstrated. Learning capability of a neuromorphic system comprising RRAM synapses and CMOS neurons has been confirmed experimentally, for the first time.

Despite the great potential of polymer microfibers in human-friendly wearable electronics, most previous polymeric electronics have been limited to thin-film-based devices due to practical difficulties in fabricating microfibrillar devices, as well as defining the active channel dimensions in a reproducible manner. Herein, we report on conducting polymer microfiber-based organic electrochemical transistors (OECTs) and their application in single-strand fiber-type wearable ion concentration sensors. We developed a simple wet-spinning process to form very conductive poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) microfibers using aqueous sulfuric acid solutions and carefully examined their electrical/electrochemical properties. In conjunction with fabricating substrate-free PEDOT:PSS microfiber-based OECT devices, the proposed novel characterization method demonstrated that the current variation ratio can be a reliable method for evaluating the device performance for sensing ion concentrations, regardless of the actual channel dimensions. Finally, we developed single-strand fiber-type skin-mountable OECTs by introducing a source-gate hybrid electrode and demonstrated that the resultant microfiber sensors can perform real-time repetitive measurements of the ion concentration in human sweat.

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Selective filtration of gas, water, and liquid or gaseous oil is essential to prevent possible environmental pollution and machine/facility malfunction in oil-based industries. Novel materials and structures able to selectively and efficiently filter liquid and vapor in various types of solutions are therefore in continuous demand. Here, we investigate selective gas-water-oil filtration using three-dimensional graphene structures. The proposed approach is based on the adjustable wettability of three-dimensional graphene foams. Three such structures are developed in this study; the first allows gas, oil, and water to pass, the second blocks water only, and the third is exclusively permeable to gas. In addition, the ability of three-dimensional graphene structures with a self-assembled monolayer to selectively filter oil is demonstrated. This methodology has numerous potential practical applications as gas, water, and/or oil filtration is an essential component of many industries.

This study combined space syntax metrics and geographic information systems (GIS)-based built-environment measures to analyze pedestrian volume in different land-use zones, as recorded in unique public data from a pedestrian volume survey of 10,000 locations in Seoul, Korea. The results indicate that most of the built-environment variables, such as density, land use, accessibility, and street design measures, showed statistically significant associations with pedestrian volume. Among the syntactic variables, global integration showed a statistically significant association with the average pedestrian volume in residential and commercial zones. In contrast, local integration turned out to be an important factor in the commercial zone. Therefore, this study concludes that the syntactic variables of global and local integration, as well as some built-environment variables, should be considered as determinant factors of pedestrian volume, though the effects of those variables varied by land-use zone. Therefore, planning and public policies should use tailored approaches to promote urban vitality through pedestrian volume in accordance with each land-use zone’s characteristics.

A preliminary feasibility study evaluates various aspects of a project such as environmental assessment, field study, technological validity, and economic feasibility. Among them, economic feasibility is the most important factor to use in selecting a road route in Korea. A proper preliminary feasibility study considers all costs incurred in the life cycle of the project, including construction costs, land acquisition costs, collateral expenses, and operation and maintenance costs. However, only construction costs are traditionally considered in the assessment of the financial viability of national road projects. In addition, while 3D modeling techniques have brought improved designs and engineering processes to the construction industries, their application in preliminary feasibility studies remains rare. We have developed a system that employs building information modeling and geographic information systems for estimating the cost of building a national road that can be applied in the preliminary feasibility stage. The proposed system is composed of three modules that estimate construction costs, land acquisition costs, and O&M costs. Based on the road route, the proposed system analyzes cross sections through the topography and subsequently determines the probable road, bridge, and tunnel sections, and their project costs. Overall, the proposed system could assist a reasonable decision making for best route selection and further facilitate improved project delivery.