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Department of Energy EngineeringIn this thesis, I observe the methods to overcome the low energy density in the supercapacitor system which is the crucial issue in energy storage industries. I challenge simple and easy approaches to achieve better capacitor properties than before by fabricating the three-dimensional structure of current collector and colloid structure of active material. First, rational design of the current collector with large surface area and high electrical conductivity is the very important factor in the hybrid-capacitor system for high performance. Nickel particles-coated three-dimensional graphene foam current collector (Ni-GF) was fabricated by two simple steps from cost-effective commercial cotton and nickel chloride, based on the growth of graphene on the surface of nickel particles. The welded nickel particles on graphene sheets and three-dimensional graphene networks enhance the electrical conductivity and various pores in graphitic carbon domains gives the high surface area, generated by the thermal decomposition of organic precursors during a carbonization or pyrolysis process. This strategy provides the high performance in the supercapacitor system as the current collector. The high surface area of Ni-GF supports a lot of reaction sites of active materials and high electrical conductivity helps the good rate capability and long-term cycle life. The prepared Ni(OH)2/Ni-GF//MnO2/Ni-GF capacitor exhibited an excellent energy density of 175 Wh kg-1 at a power density of 722 W kg-1 for a two-electrode system. Also, I improve the weakness of supercapacitors such as low energy density by utilizing cobalt and nickel ion colloidal electrodes on a carbonized cotton. Ni2+ and Co2+-coated carbonized cotton (NC/CC) were prepared by simple and rapid fabrication process. The metal colloidal electrode on three-dimensional carbon foam provides many active sites, which leads to a lot of redox reactions in whole colloids of CNFs. CNFs were optimized by adjusting the contents of Co2+ and Ni2+ on carbon foams, and it showed high capacitance and stable cycle stability. The optimized NC/CC//Mn/CC capacitor leads to overcome a limitation of supercapacitor and to achieve the enhancement of capacitor properties. The outstanding performance of NC/CC//Mn/CC is attributed to the increased active sites of metal colloidal electrodes as well as to the good stability for carbon foams. These excellent electrochemical results have the great potential for energy storage devices with high values of energy density and power density.ope

Effect of Trust in Metaverse on Usage Intention through Technology Readiness and Technology Acceptance Model

The fourth industrial revolution enhanced the development of information technology in all fields and opened up possibilities. A lot of attention is focused on the future possibilities opened up by the metaverse, the core of information technology. Metaverse will have a big impact on reality and the near future. Metaverse is a virtual world that fuses physical and digital reality. Various commerce such as healthcare, instruction, business, and land are foundation to utilize metaverse knowledge in their regular work. There is a series of processes in the stage where newly developed technology is introduced to general users. In order for a new technology to become a user-friendly technology, it is necessary to verify the technology. It can be said that it is hard to derive the operator\u27s usage intention in a state where user trust for new technology is not verified. In the metaverse environment, it is necessary to first verify the trust for new technologies. This study is expected to understand usage intention through the process of checking trust in metaverse, and to become basic data for the popularization of metaverse knowledge. The meaning of this research is to inspect the influence relationship of trust in metaverse on usage intention through Technology Readiness (TR) and Technology Acceptance Model (TAM). Statistical package (SPSS23.0) was used for basic numerical examination of the questionnaire. Hypothesis test was performed using the structural equation package Smart PLS 3.0. Discriminant validity and concentration validity of the questionnaire were verified. As parameters that trust in metaverse effects, TR and TAM were set. As factors constituting TR, it was separated into optimism, innovativeness, discomfort, and insecurity. The TAM is separated into perceived usefulness and perceived ease of use. The outcomes of the study are as follows. First, trust in metaverse had a significant effect on TR. Second, TR was partially adopted in the TAM. Innovativeness and perceived usefulness had no significant effect. Third, TAM significantly influences usage intention. Fourth, perceived ease of use did not significantly influence perceived usefulness

Entropic, electrostatic, and interfacial regimes in concentrated disordered ionic emulsions

We develop a free energy model that describes two key thermodynamic properties, the osmotic pressure Π and the linear elastic shear modulus G′p (i.e. plateau storage modulus), of concentrated monodisperse emulsions which have isotropic, disordered, droplet structures, and are stabilized using ionic surfactants. This model effectively incorporates the concept of random close packing or jamming of repulsive spheres into a free energy F that depends on droplet volume fraction ϕ and shear strain γ both below and above the a critical jamming point ϕc ≈ 0.646. This free energy has three terms: entropic, electrostatic, and interfacial (EEI). By minimizing F with respect to an average droplet deformation parameter that links all three terms, we show that the entropic term is dominant for ϕ well below ϕc, the electrostatic term is dominant for ϕ near but below ϕc, and the interfacial term dominates for larger ϕ. This EEI model describes measurements of G′p(ϕ) for charge-stabilized uniform emulsions having a wide range of droplet sizes, ranging from nanoscale to microscale, and it also is consistent with measurements of Π(ϕ). Moreover, it describes G′p(ϕ) for similar nanoemulsions after adding non-amphiphilic salt, when changes in the interfacial tension and the Debye screening length are properly taken into account. By unifying existing approaches, the EEI model predicts constitutive properties of concentrated ionic emulsions that have disordered, out-of-equilibrium structures through near- equilibrium free energy minimization, consistent with random driving Brownian excitations

The role of NGOs for low-income groups in Korean society

SUMMARY: This paper describes the increasingly important role of NGO

A study on the changes in gait characteristics by applying sub-threshold vibration stimulus in the ankle

This study was conducted to suggest the potential use of a mechanical vibration stimulus in the ankle to correct gait abnormalities. As for the mechanical vibration stimulus, different locations and durations are suggested based on the detection results of real-time gait patterns. 5 young males participated in this study. They were asked to perform assigned gait tasks when either a threshold or sub-threshold stimulus was applied in the tibialis anterior and Achilles tendon. The analysis results of gait cycle and muscle activity showed the changes on gait cycle, the activity pattern of used muscle for gait and the movement pattern of the ankle were observed based on the applied locations of vibration stimulus. Also, the result of sub-threshold stimulus showed similar effects as that of threshold stimulus. As such, the mechanical vibration stimulus was considered to affect gait by being adjusted its characteristics and local stimulus also would affect human body systemically. The result of this study can be used as basic data for the correction of individual’s specific gait abnormality and rehabilitation using vibration stimulus

Effects of muscular response for the intensity of vibratory stimulus applied on the ankle tendon

The present study was conducted to measure the individual threshold value for the somatosensory system of the human body, the thresholds value of vibratory stimulus were assessed through the ascent and descent methods. In the interests of the attainment of this study`s goal, comparing the thresholds value measured and change of state of the muscles when applied on the ankle tendon connected to muscles, changes in threshold measurement accuracy due to the differences in measuring methods were discussed. The experiment was conducted by constructing systems to stimulate somethetic sensibility by vibratory stimulus, ultrasound imaging system and EMG system. Five adult males were involved in this experiment. According to the results of experiments, the threshold value of somatosensory stimulation measured by the ascent method was greater than the threshold values measured by the descent method. And the muscular response to the somatosensory stimulation applied to the tibialis anterior tendon showed a larger rate of change with the ascending stimulus than with the descending stimulus. The results of this study could serve as a basis to discuss the reliability of the measurement method of the human body’s individual threshold value for the somatosensory system through the ascent and descent methods and can be used as reference data for the integration and performance threshold measurement methods

Strong and Reversible Adhesion of Interlocked 3D-Microarchitectures

Diverse physical interlocking devices have recently been developed based on one-dimensional (1D), high-aspect-ratio inorganic and organic nanomaterials. Although these 1D nanomaterial-based interlocking devices can provide reliable and repeatable shear adhesion, their adhesion in the normal direction is typically very weak. In addition, the high-aspect-ratio, slender structures are mechanically less durable. In this study, we demonstrate a highly flexible and robust interlocking system that exhibits strong and reversible adhesion based on physical interlocking between three-dimensional (3D) microscale architectures. The 3D microstructures have protruding tips on their cylindrical stems, which enable tight mechanical binding between the microstructures. Based on the unique 3D architectures, the interlocking adhesives exhibit remarkable adhesion strengths in both the normal and shear directions. In addition, their adhesion is highly reversible due to the robust mechanical and structural stability of the microstructures. An analytical model is proposed to explain the measured adhesion behavior, which is in good agreement with the experimental results