• Journal of Hydrogen and New Energy
• /
• v.29 no.6
• /
• pp.587-595
• /
• 2018

Recently, research is being conducted to use a fuel cell as a power source of unmanned aircraft. However, safety standards about applying fuel cells to unmanned aircraft are insufficient. In this paper, to improve the safety of the fuel cells for unmanned aircraft is experimentally studied. For this reason, standards for safety of fuel cells were analyzed. And influence of vibration among the evaluation items related to the safety of the fuel cell for unmanned aircraft was discussed. In order to, at constant intervals, vibration was applied to the fuel cell, then the performance was measured, the measurement items were gas tightness, polarization curve, frequency response analysis (FRA). A total of 220 hours was experimented at 20 hour intervals. the result of vibration test, gas leakage rate was a maximum of -0.04826 kPa/min and Polarization curve reached a maximum of 1.0103 times of the initial value, the charge transfer resistance reached a maximum of 1.0104 times of the initial value. This research indicate that performance of fuel cell is affected by vibration and this study is expected to contribute to the safety of fuel cell for unmanned aircraft.

• Advances in nano research
• /
• v.7 no.4
• /
• pp.249-263
• /
• 2019

In the current paper, an exact solution method is carried out for analyzing the thermo-mechanical vibration of curved FG nano-beams subjected to uniform thermal environmental conditions, by considering porosity distribution via nonlocal strain gradient beam theory for the first time. Nonlocal strain gradient elasticity theory is adopted to consider the size effects in which the stress for not only the nonlocal stress field but also the strain gradients stress field is considered. It is perceived that during manufacturing of functionally graded materials (FGMs) porosities and micro-voids can be occurred inside the material. Material properties of curved porous FG nanobeam are assumed to be temperature-dependent and are supposed to vary through the thickness direction of beam which modeled via modified power-law rule. Since variation of pores along the thickness direction influences the mechanical and physical properties, porosity play a key role in the mechanical response of curved FG nano-structures. The governing equations and related boundary condition of curved porous FG nanobeam under temperature field are derived via the energy method based on Timoshenko beam theory. An analytical Navier solution procedure is utilized to achieve the natural frequencies of porous FG curved nanobeam supposed to thermal loading. The results for simpler states are confirmed with known data in the literature. The effects of various parameters such as nonlocality parameter, porosity volume fractions, thermal effect, gradient index, opening angle and aspect ratio on the natural frequency of curved FG porous nanobeam are successfully discussed. It is concluded that these parameters play key roles on the dynamic behavior of porous FG curved nanobeam. Presented numerical results can serve as benchmarks for future analyses of curve FG nanobeam with porosity phases.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.23 no.5
• /
• pp.48-59
• /
• 2019

In recent years, the type of bridge where cables such as suspension bridge and cable-stayed bridge are the main factors in the construction of long-range bridges has been soaring. The effects of cables on these structures are very large, and for structural analysis, it is necessary to study the cable and the structural changes according to the mode characteristics of the cables. In particular, cables are directly connected to camber adjustment, which conveys load effects on girders to tower, and are important components in the overall structure, and since the initial tension on the construction is compared with the tension over time, this study was conducted to help identify the condition of the bridge's aging and abnormalities. Therefore, in this study, the characteristics of the mode from the mode analysis through the impact hammer to the mass of the cable and the change in the length of the cable are analyzed.

• The Journal of Korean Society for School & Community Health Education
• /
• v.20 no.2
• /
• pp.81-91
• /
• 2019

Objectives: It helps dental clinic to work 1:1 consulting and select the properties of the Kakao Talk message. The study was designed to determine the influence of users cognitive and emotional responses by message attribute that affect intention of use of dental clinic. Methods: This study targeted 297 peple Kakao Talk users aged 20-50 s, in Seoul, Gyeonggi-do and Incheon from, February 6 to April 7, 2017. We analyzed the data with frequency analysis, t-test, one-way ANOVA, and multiple regression analysis by using SPSS ver 24.0(SPSS Inc, Chicago, USA). The significance level for significance was set at 0.05. Results: Among the user's responses about the event type Kakao talk message, the ease(${\beta}=0.121$, p<0.01), usefulness(${\beta}=0.148$, p<0.001), affinity(${\beta}=0.471$, p<0.001), satisfaction(${\beta}=0.249$, p<0.001). affected intention of use of dental clinic. Among the user's responses about the dental information type, the ease(${\beta}=0.150$, p<0.05), expertise(${\beta}=0.151$, p<0.05), satisfaction(${\beta}=0.237$, p<0.001) affected intention of use of dental clinic(p<0.05). Among the user's responses about the general public relations type, the expertise(${\beta}=0.254$), affinity(${\beta}=0.193$), satisfaction(${\beta}=0.474$) affected intention of use of dental clinic(p<0.001). Conclusion: It is necessary to elicit a positive intention of use of dental clinic through a highly emotional response from the users to improve the image of the dental clinic and to attract patients.

• Journal of Korean Academy of Nursing
• /
• v.49 no.4
• /
• pp.361-374
• /
• 2019

Purpose: This study was conducted to evaluate the effectiveness of autogenic training on stress responses through a systematic review and meta-analysis. Methods: A systematic search was conducted using eight core electronic databases (Embase, CENTRAL, Medline, CINAHL, PsycInfo, DBpia, KISS, and RISS). To estimate the effect size, a meta-analysis of the studies was performed using RevMan 5.3.5 program. Results: A total 21 studies out of 950 studies were included in the review, and 11 were included for meta-analysis. These studies showed that autogenic training decreased anxiety and depression, and increased the high frequency of heart rate variability. Calculations to understand the effect of autogenic training on anxiety, through a meta-analysis, observed a reduction effect of anxiety score by 1.37 points (n=85, SMD=-1.37: 95% CI -2.07 to -0.67), in the studies on short-term intervention targeting healthy adults. On the other hand, similar calculations to understand the effect of autogenic training on depression observed, a reduction effect on the depression score by 0.29 point (n=327, SMD=-0.29: 95% CI -0.50 to -0.07), in the studies on long term intervention targeting the patient group. Conclusion: Autogenic training is effective for adults' stress management, and nurses will be able to effectively perform autogenic training programs for workers' stress relief at the workplace.

• Food Science of Animal Resources
• /
• v.39 no.4
• /
• pp.565-575
• /
• 2019

This study evaluated Campylobacter jejuni risk in ground meat products. The C. jejuni prevalence in ground meat products was investigated. To develop the predictive model, survival data of C. jejuni were collected at $4^{\circ}C-30^{\circ}C$ during storage, and the data were fitted using the Weibull model. In addition, the storage temperature and time of ground meat products were investigated during distribution. The consumption amount and frequency of ground meat products were investigated by interviewing 1,500 adults. The prevalence, temperature, time, and consumption data were analyzed by @RISK to generate probabilistic distributions. In 224 samples of ground meat products, there were no C. jejuni-contaminated samples. A scenario with a series of probabilistic distributions, a predictive model and a dose-response model was prepared to calculate the probability of illness, and it showed that the probability of foodborne illness caused by C. jejuni per person per day from ground meat products was $5.68{\times}10^{-10}$, which can be considered low risk.

• Steel and Composite Structures
• /
• v.32 no.6
• /
• pp.807-819
• /
• 2019

In recent earthquakes, the failure of ceiling systems has been one of the most widely reported damage and the major cause of functionality interruption in some buildings. In an effort to mitigate this damage, some scholars have studied a series of ceiling systems including plaster ceilings and mineral wool ceilings. But few studies have involved the backdrop metal ceiling used in some important constructions with higher rigidity and frequency such as the main control area of nuclear power plants. Therefore, in order to evaluate its seismic performance, a full-scale backdrop metal ceiling system, including steel runners and metal panels, was designed, fabricated and installed in a steel frame in this study. And the backdrop metal ceiling system with two perimeter attachments variants was tested: (i) the ends of the runners were connected with the angle steel to form an effective lateral constraint around the backdrop metal ceiling, (ii) the perimeter attachments of the main runner were retained, but the perimeter attachments of the cross runner were removed. In the experiments, different damage of the backdrop metal ceiling system was observed in detail under various earthquakes. Results showed that the backdrop metal ceiling had good integrity and excellent seismic performance. And the perimeter attachments of the cross runner had an adverse effect on the seismic performance of the backdrop metal ceiling under earthquakes. Meanwhile, a series of seismic construction measures and several suggestions that need to be paid attention were proposed in the text so that the backdrop metal ceiling can be better applied in the main control area of nuclear power plants and other important engineering projects.

• Journal of Korean Association for Spatial Structures
• /
• v.19 no.1
• /
• pp.117-126
• /
• 2019

Micro-Electro-Mechanical Systems (MEMS) sensors have been widely used in Structural Health Monitoring due to their convenience and lower costs in comparison to conventional sensors. Triggered measurements are relevant in events such as earthquakes because unlike continuous measurements, they only record the structural response once an event happens. This is more cost effective and it makes the data more manageable because only the required measurements from the event are recorded. The most common method of triggering is amplitude triggering. However, lower input amplitudes (less than 0.1g) cannot be triggered by using this method. In this paper, sound triggering was introduced to allow triggered measurements for lower input amplitude values. The performance of the sound triggering and amplitude triggering were compared by a series of shaking-table tests. It was seen that sound-triggering method has a wider frequency (0.5~10Hz) and amplitude (0.01~1.0g) range of measurements. In addition, the sound triggering method performs better than the amplitude triggering method at lower amplitudes. The performance of the amplitude triggering, in terms of the triggering being simultaneous improves at higher input amplitudes.

• Journal of the Semiconductor & Display Technology
• /
• v.18 no.1
• /
• pp.15-20
• /
• 2019

Inspection and measurement of surface quality is one of the most critical processes for manufacturing products such as semiconductor wafers, sapphire substrates, and display panels. The vibrations of the inspection and measurement devices are supposed to be the most dominant factors for severe measurement errors and longer measuring time. In this study, dynamic characteristics of an inspection and measurement device are analyzed through frequency response experiment and computer simulation to obtain parameters such as frequencies, magnitudes, mode shapes, and periods of vibrations. And then an active damper which consists of sensor, interface board, and actuator is designed based on the parameters to formulate the most effective reaction signal to suppress the vibrations which is generated by an interface board, and provided by an actuator. If the vibrations are measured by the sensor, the active damper immediately generates and provides the corresponding reaction signal to inspection and measurement device. The result shows that the active damper can suppress structural vibrations effectively and reduce measuring time of the device and enhance the productivity.

• Steel and Composite Structures
• /
• v.30 no.1
• /
• pp.31-46
• /
• 2019

In the present study, the various dynamic properties of MWCNT embedded fiber reinforced polymer uniform and tapered composite (MWCNT-FRP) plates are investigated. Various configurations of a tapered composite plate with ply-drop off and uniform composite plate have been considered for the development of the finite element formulation and experimental investigations. First order shear deformation theory (FSDT) has been used to derive the kinetic and potential energy equations of the hybrid composite plates by including the effect of rotary inertia, shear deformation and non-uniformity in thickness of the plate. The governing equations of motion of FRP composite plates without and with MWCNT reinforcement are derived by considering a nine- node rectangular element with five degrees of freedom (DOF) at each node. The effectiveness of the developed finite element formulation has been demonstrated by comparing the natural frequencies and damping ratio of FRP composite plates without and with MWCNT reinforcement obtained experimentally. Various parametric studies are also performed to study the effect of CNT volume fraction and CNT aspect ratio of the composite plate on the natural frequencies of different configurations of CNT reinforced hybrid composite plates. Further the forced vibration analysis is performed to compare the dynamic response of the various configurations of MWCNT-GFRP composite plate with GFRP composite plate under harmonic excitations. It was observed that the fundamental natural frequency and damping ratio of the GFRP composite plate increase approximately 8% and 37% respectively with 0.5wt% reinforcement of MWCNT under CFCF boundary condition. The natural frequencies of MWCNT-GFRP hybrid composite plates tend to decrease with the increase of MWCNT volume fraction beyond 2% due to agglomeration of CNT's. It is also observed that the aspect ratio of the CNT has negligible effect on the improvement of dynamics properties due to randomly orientation of CNT's.