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Rice-like Tellurium Thin Films Deposited by a Galvanic Displacement Reaction and Ultra-high Sensing Response to Hydrogen Sulfide (H2S) Gas at Room temperature
No full textIn this study, we present the synthesis of rice-like tellurium (Te) thin films using a galvanic displacement reaction (GDR, a substrate.sacrificial, electro-less deposition technique) on a silicon wafer and their response to hydrogen sulfide (H2S) gas at room temperature. The thin films were composed of rice-like Te nano grains, whose thickness and crystallinity were controlled by adjusting the reaction time of the GDR. As the reaction time increased, the as-fabricated rice-like Te-based gas sensors showed full response and recovery. The sensors with an optimized GDR showed ultra-high sensing response to H2S (1000% at 100 ppm of H2S) under ambient sensing conditions, with excellent response toward H2S gas (ranging from 15 ppb to 90 ppm). Additionally, the optimized sensor shows relatively high response toward H2S gas as compared to other gases such as NO2, NH3, and CO. Together, these results indicate that the rice-like tellurium (Te) thin films have great potential for applications in high-performance (HS)-S-2 gas sensors that are capable of operating at room temperature.This research was supported by Nano center dot Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (No. 2016M3A7B4900044) and by the Human Resources Development program (No. 20174030201830) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) funded by the Korean government Ministry of Trade, Industry, and Energy
Fabrication of Pressure-Sensitive Multiwalled Carbon Nanotubes-Poly(methyl methacrylate) Nanocomposites for Pressure-Sensing Applications
No full textIn this study, we fabricated novel, pressure-sensitive nanocomposites through two different methods. These materials were thoroughly evaluated and compared with one another. Multiwalled carbon nanotubes (MWCNTs) were added to thermoplastic polyurethane (TPU) by melt mixing and to Poly(methyl methacrylate) (PMMA) beads of different sizes to make the first type of sample. A solution mixing method was used to coat PMMA beads of different sizes with MWCNTs, and then the TPU polymer was added to make another nanocomposite. The effects of different PMMA bead sizes on the pressure-sensing properties of both nanocomposites were studied by applying different external loads. PMMA beads were used to increase the internal volume and achieve a segregated electro-conductive network structure, leading to an early percolation threshold. Scanning electron and Raman microscopy were used to study the morphology of the nanocomposites. The electrical and thermal conductivities of the nanocomposites were also investigated under different applied loads, and the two methods were compared. The electrical responses of the nanocomposites under different applied pressures demonstrated a linear decrease in the electrical resistivity with increasing applied external load, thereby confirming that these novel nanocomposites are suitable for use as pressure-sensing materials; they also show repeatability in their electrical response when an external load was applied repeatedly. These materials represent ideal candidates for use in pressure-sensitive devices
Piezoelectric and ferroelectric characteristics of P(VDF-TrFE) thin films on Pt and ITO substrates
No full textOrganic P(VDF-TrFE) 70/30 copolymer thin films were fabricated on Pt/Ti/SiO2/Si(1 1 1) and ITO/glass substrates at 140 degrees C using a spin coater. Both P(VDF-TrFE) thin films exhibited ferroelectric /beta-phase crystallinity, as confirmed by X-ray diffraction analysis. The polarization-electric hysteresis loops of the P (VDF-TrFE) thin films on the Pt and indium-tin-oxide substrates showed high remnant polarizations of 15.5 and 11.8 mu C/cm(2), respectively. Atomic force microscopy characterization showed rod-like features of the P(VDF-TrFE) thin films on both substrates, where larger rod diameters were observed on the Pt substrate compared to those fabricated on the ITO substrate. Piezoelectric force microscopy measurements further confirmed the superior piezoelectric and ferroelectric properties of the P(VDF-TrFE) thin films on the Pt substrate compared to those on the ITO substrate, which arose from the increased diameter of the rod-like features. (C) 2018 Elsevier B.V. All rights reserved.This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (No. 2018R1A6A3A11045896). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP, No. NRF-2017R1C1B5076821) and supported by research funds for newly appointed professors of Chonbuk National University in 2017. This research is supported by "Rediscovery of the Past R&D Result" through the Ministry of Trade, Industry and Energy (MOTIE) and the Korea Institute for Advancement of Technology (KIAT) (Grant No.: P0004074)
Feature Selection Method from Multiclass Text with Class Imbalance Problem
No full textA text classification model in which one of the class variables is biased to the majority class typically classifiesmost documents into the majority class to enhance the overall classification accuracy. It is called a classimbalance problem. This study proposes a feature selection method based on simplified chi-square statistics toselect features in each class for developing a robust model to the problem. Proposed method and typical featureselection methods are compared by Reuter21578 data. Experiment shows that the proposed method is superior totypical feature selection methods in terms of naïve Bayes and support vector machine which are robust to theclass imbalance problem
The Effects of Authentic Leadership on Innovation Behavior and Job Satisfaction through Positive Psychological Capital
No full text본 연구는 공군의 소령과 중령을 대상으로 진성리더십과 긍정심리자본, 혁신행동, 직무만족 간의 관계를 파악하고, 긍정심리자본의 매개효과와 관리자 경험의 조절효과를 분석하였다. 실증분석결과는 다음과 같다. 첫째, 긍정심리자본은 진성리더십과 혁신행동 간의 사이에서 전부매개하고 있는 것으로 나타났다. 둘째, 진성리더십이 직무만족에 미치는 직접효과는 유의한 반면, 긍정심리자본이 직무만족에 미치는 직접효과는 유의하지 않은 것으로 나타났다. 셋째, 관리자 경험 유무는 긍정심리자본과 혁신성향 간의 관계에서 유의한 조절효과가 나타났다. The purpose of this study is to analyze the relationship among the authentic leadership, positive psychological capital, innovation behavior(innovation activity and innovation propensity) and job satisfaction. The results of the empirical analysis are as follows. First, authentic leadership directly effects positive psychological capital, and positive psychological capital also effects innovation behavior directly. But authentic leadership could not effect directly toward innovation behavior. This result shows that authentic leadership can effect the innovation behavior through psychological capital. Second, authentic leadership directly effects job satisfaction, whereas positive psychological capital does not effect directly job satisfaction. Third, the managerial experience showed a significant moderating effect on the relationship between positive psychological capital and innovation propensity, but not on the relation of innovation activity. This implies positive psychological capital is an important factor that induces innovation behavior in the military organization
Optimization of Spectrum Utilization in Cooperative Spectrum Sensing
No full textThis paper presents an analytical framework for the probability of spectrum hole utilization (PSHU) of a cognitive radio system with soft cooperative spectrum sensing (CSS) under a practical consideration of fixed frame structure. In practical systems, the length of a time-frame is generally fixed, where the time-frame consists of sensing, reporting, and transmission durations. Thus, increasing sensing and reporting time duration in cooperative spectrum sensing improves the probability of successful detection of the primary user's (PU) presence or the absence but reduces transmission time duration, which results in a lower PSHU. A large reporting duration is required when more secondary users (SUs) report their sensed information to the fusion center (FC) and/or multiple bits are used by each SU in soft cooperative spectrum sensing. Thus, reporting time in terms of the number of SUs and reporting bits also have a similar effect on PSHU. Based on this interesting trade-off between PSHU and the sensing and reporting time duration, this paper analyzes the impact of an increasing number of SUs and reporting bits on PSHU.This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1D1A1B03934277)
A Review of Static and Dynamic Forced Performance of Step Thrust Bearings
No full text스러스트 베어링은 축방향 하중을 지지하고 마찰을 감소시키는 베어링이다. 스러스트 베어링의 성능은 하중지지력이 중요한 요소이며 이를 향상시키기 위한 연구가 필수적이다. 스텝 스러스트 베어링은 패드가 스텝 형상으로 이루어진 베어링으로 설계가 단순하고 하중지지력이 높은 장점이 있다. 본 연구에서는 스텝 스러스트 베어링의 최근 연구동향을 분석하였다. 연구 동향의 내용으로는 크게 스러스트 베어링의 하중지지능력 및 동적 특성을 향상시키기 위한 해석적 연구와 이를 증명하기 위한 실험적 연구로 구분하여 분석을 진행하였다
Coordinating Supply-Chain Management under Stochastic Fuzzy Environment and Lead-Time Reduction
No full textIn this paper, a supply-chain (SC) coordination method based on the lead-time crashing is proposed for a seller-buyer system. By considering different transportation modes, we control the lead-time (LT) variability. For the first time, we have attempted to determine the impact of the reliable and unreliable seller in a continuous-review supply-chain model under the stochastic environment. The authors discussed two reliability cases for the seller. First, we consider the seller is unreliable and in the second case, the seller is reliable. In addition, the demand during the lead time is stochastic with the known mean and variance. The proposed approach tries to find an optimal solution that performs well without a specific probability distribution. Besides, a discrete investment is made to reduce the setup cost, which will indirectly help supply-chain members to increase the total profit of the system. In the proposed model, the seller motivates the buyer by reducing lead time to take part in coordinating decision-making for the system's profit optimization. We derive the coordination conditions for both members, the seller and the buyer, under which they are convinced to take part in the cooperative decision-making plan. Therefore, lead-time crashing is the proposed incentive mechanism for collaborative supply-chain management. We use a fixed-charge step function to calculate the lead-time crashing cost for slow and fast shipping mode. We give two numerical examples to validate the proposed models and demonstrate the service-level enhancement under the collaborative supply-chain management in case of an unreliable seller. Concluding remarks and future extensions are discussed at the end
Investigating the preferences of older adults concerning the design elements of a companion robot
No full textResearchers have reported that companion robots have had positive effects on older adults with depression. However, there has been little quantitative analysis on the relationship between robot design and depression. To address this, we surveyed 191 older adults and investigated the impact of age, gender and depression level on design preferences for companion robots. We focused on toy-sized companion robots and evaluated three design elements: type, weight and material. The findings show that baby-type robots were the most preferred by older adults. They favoured the lightest weights and microfibre materials, regardless of the independent variables. Moreover, robot weight preferences varied significantly with the level of depression. Highly depressed older adults disliked heavy robots. These preliminary findings suggest that companion robots need to be designed with careful consideration of their physical characteristics and potential psychological effects
A Single-stage manufacturing model with imperfect items,inspections,rework, and planned backorders
No full textEach industry prefers to sell perfect products in order to maintain its brand image. However, due to a long-run single-stage production system, the industry generally obtains obstacles. To solve this issue, a single-stage manufacturing model is formulated to make a perfect production system without defective items. For this, the industry decides to stop selling any products until whole products are ready to fulfill the order quantity. Furthermore, manufacturing managers prefer product qualification from the inspection station especially when processes are imperfect. The purpose of the proposed manufacturing model considers that the customer demands are not fulfilled during the production phase due to imperfection in the process, however customers are satisfied either at the end of the inspection process or after reworking the imperfect products. Rework operation, inspection process, and planned backordering are incorporated in the proposed model. An analytical approach is utilized to optimize the lot size and planned backorder quantities based on the minimum average cost. Numerical examples are used to illustrate and compare the proposed model with previously developed models. The proposed model is considered more beneficial in comparison with the existing models as it incorporates imperfection, rework, inspection rate, and planned backorders