• Journal of Korean society of Dental Hygiene
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• v.4 no.2
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• pp.225-236
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• 2004

It has been suggested in research results thai dental hygienists have high risk of carpal tunnel syndrome, mainly caused by the repeated motion of extensor and flexor or the use of vibration tools, compared to other occupations. To find out the situation of the carpal tunnel syndrome of dental hygienists, who are exposed to work-related musculoskeletal disorders, this study used 132 questionnaires given on May 22, 2004, the period of continuing education of the first half year in the Gwangju Jeonnam area, and obtained the following results. 1. Subjects worked at a dental ciinic(32.6%), a hospital(31.8%), and a public health center(35.6%). Age by work was under 24 in a clinic(17.4%) and a hospital(15.9%), and over 30 in a public health center(35.6%). 2. In practice conducted over one time a day, a scaling accounted for 90.7% in a doctor's office; 595% in a hospital; and 3.0% in a public health center, suggesting significant difference(p<0.01). Pit and fissure sealant accounted for 53.5% in a clinic; 53.2% in a hospital; and 95% in a public health center, also suggesting significant difference(p0.01). 3. Symptoms of carpal tunnel syndrome appeared in a wrist(12.1%), a right hand(14.4%), and a left hand(5.3%). 4. In case of temporary crown practice, symptoms appeared in a wrist(22.0%), a right hand(14.0%), and a left hand(4.0%), suggesting significant difference(p<0.01). The above results showed that 12.1% of dental hygienists was exposed to carpal tunnel syndrome. Thus, it is considered very important that dental hygienists should be given education of the danger of continuous work in certain motions and prevention education of improving repeated position, and make efforts to reinforce self-control ability.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.1
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• pp.37-44
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• 2016

Optical fiber temperature sensing systems have incomparable advantages over traditional electrical-cable-based monitoring systems. However, the fiber optic interrogators and sensors have often been rejected as a temperature monitoring technology in real-world industrial applications because of high cost and over-specification. This study proposes a multiplexed fiber optic temperature monitoring sensor system using an economical Optical Time-Domain Reflectometer (OTDR) and Hard-Polymer-Clad Fiber (HPCF). HPCF is a special optical fiber in which a hard polymer cladding made of fluoroacrylate acts as a protective coating for an inner silica core. An OTDR is an optical loss measurement system that provides optical loss and event distance measurement in real time. A temperature sensor array with the five sensor nodes at 10-m interval was economically and quickly made by locally stripping HPCF clad through photo-thermal and photo-chemical processes using a continuous/pulse hybrid-mode laser. The exposed cores created backscattering signals in the OTDR attenuation trace. It was demonstrated that the backscattering peaks were independently sensitive to temperature variation. Since the 1.5-mm-long exposed core showed a 5-m-wide backscattering peak, the OTDR with a spatial resolution of 40 mm allows for making a sensor node at every 5 m for independent multiplexing. The performance of the sensor node included an operating range of up to $120^{\circ}C$, a resolution of $0.59^{\circ}C$, and a temperature sensitivity of $-0.00967dB/^{\circ}C$. Temperature monitoring errors in the environment tests stood at $0.76^{\circ}C$ and $0.36^{\circ}C$ under the temperature variation of the unstrapped fiber region and the vibration of the sensor node. The small sensitivities to the environment and the economic feasibility of the highly multiplexed HPCF temperature monitoring sensor system will be important advantages for use as system-integrated temperature sensors.

• Journal of KSNVE
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• v.8 no.6
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• pp.1166-1171
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• 1998

The influences of the coupler consisting of stiffness and mass between neighboring two spans on mode localization are studied theoretically, and the results are confirmed by numerical examples. The mass of the coupler makes a structure sensitive to mode localization especially in higher modes while the stiffness does in all modes. A new type of delocalization phenomenon is observed for the first time in some modes for which mode localization does not occur or is very weak although structural disturbances are severe. A spring-mass system consisting of two substructures and a coupler connecting them is considered in the part of analytical study. As example structures for numerical analysis. simply supported continuous two-span beams with a coupler having a rotational stiffness and a mass moment of inertia on the mid support are considered.

• Journal of the Ergonomics Society of Korea
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• v.23 no.3
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• pp.121-134
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• 2004

A research project was conducted to study work-related musculoskeletal disorders （MSDs） at subway train repair plant in Korea. The project was consisted of 4 main parts; education on the topics of MSDs for all workers, symptom survey, medical check-up, investigation of MSD risk factors. The result of symptom survey showed that 95.2％ of the respondents complained pains on at least one part of the body. After cross-sectional analysis of various information and risk factors, 86.8％ of respondents were considered as active health surveillance level 1 that require continuous monitoring on their symptoms and working conditions. And 57.1％ of the respondents were considered as active health surveillance level 2 that needed medical check-ups for proper medical treatment. The analysis of occupational risk factors revealed that handling of heavy object (46.15％) and repeated awkward postures (46.15％) were two most contributing risk factors for the on-set of MSD at this work site followed by static strain (7.7％), and vibration and impact (3.8％). Medical examination was performed by an industrial medicine MD on 156 workers those considered as active health surveillance level 2. The result showed that 35 workers (20.7％) were considered as MSD patient group at severe level, and 68.6 workers (68.6％) were considered as moderate group and 18 workers (10.6％) were considered minor or normal group those have no symptom.

• The Journal of the Korean dental association
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• v.49 no.4
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• pp.219-226
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• 2011

Snoring and obstructive sleep apnea (OSA) are common sleep disordered breathing conditions. Habitual snoring is caused by a vibration of soft tissue of upper airway while breath in sleeping, and obstructive sleep apnea is caused by the repeated obstructions of airflow for a sleeping, specially airflow of pharynx. Researchers have shown that snoring is the most important symptom connected with the obstructive sleep apnea syndrome The treatment is directed toward improving the air flow by various surgical and nonsurgical methods. The current surgical procedures used are uvulopalatopharyngoplasty(UPPP), orthognathic surgery, nasal cavity surgery. Among the nonsurgical methods there are nasal continuous positive air pressure(CPAP), pharmacologic therapy. weight loss in obese patient, oral appliance(sleep splint). Sleep splint brings the mandible forward in order to increase upper airway volume and prevents total upper airway collapse during sleep. However, the precise mechanism of action is not yet completely understood, especially aerodynamic factor. The aim of this study evaluated the effect of conservative treatment of snoring and OSAS by sleep splint through measured aerodynamic change by an aerophone II. We measured a airflow, sound pressure level, duration, mean power from overall airflow by aerophone II mask. The results indicated that on a positive correlation between a decrease in maximum airflow rate and a decrease in maximum sound pressure level, on a negative correlation between a decrease in maximum airflow rate and a increase in duration.

• Fire Science and Engineering
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• v.18 no.4
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• pp.57-63
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• 2004

We investigated heat properties of connection terminal in residual current protective devices(RCD) according to contact pressure for low voltage appliance. And we analyzed voltage and current waveform and oxide propagation when the poor-contact happened between terminal and wire. When contact pressure between terminal and connection wire was not applied, the heat was generated and an oxide was formed on the surface of the wire. The temperature of the insulation surrounding terminal was ascended sharply by poor-contact, micro-sparks and continuous arc sound happened in interior terminal. When the poor-contact by vibration occurred inner conductor of terminal and wire, an oxide was propagated on contact surface and the temperature was increased at 869℃. Thus, we found that the risk of electrical disaster is high in terminal and connection wire parts.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.2
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• pp.103-110
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• 2018

Most of the intake facilities of small agricultural reservoirs are conduits and they are regarded as serious defects due to the structural weakness that penetrates the body of the dam, and countermeasures are needed. This study suggests the application method of siphon type water intake facility by hydraulic model test and physical scale model test of siphon type water intake facility which has high safety and easy maintenance. Experimental results show that sufficient flow rate can be secured for the purpose of intaking water according to the differential head between the reservoir and the discharge part, and the flow rate can be controlled by the valve. The negative pressure was -31.5 kPa, and vibration and noise did not occur during the operation of the siphon. The maximum flow velocity in the discharge outlet was 1.11 m/s which meets the criterion for irrigation canals. Therefore, scour risk would be very low. As a result of the inflow distribution experiment, even if the inflow part is separated by only about 0.8 m, the flow velocity is remarkably decreased, so that the clogging by debris would not appear. When the pump was operated only once for the first time and the inside of the siphon was filled with water, continuous operation was possible by only valve operation. The results of this study are expected to be used for the design guidelines of the water intake facilities and improve safety and maintenance convenience of agricultural reservoirs.

• Journal of Electrical Engineering and Technology
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• v.10 no.5
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• pp.2018-2030
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• 2015

A two stage ac drive configuration consisting of a single-phase line commutated rectifier and a three-phase voltage source inverter (VSI) is very common in low and medium power applications. The deterministic pulse width modulation (PWM) methods like sinusoidal PWM (SPWM) could not be considered as an ideal choice for modern drives since they result mechanical vibration and acoustic noise, and limit the application scope. This is due to the incapability of the deterministic PWM strategies in sprawling the harmonic power. The random PWM (RPWM) approaches could solve this issue by creating continuous harmonic profile instead of discrete clusters of dominant harmonics. Insufficient filtering at dc link results in the amplitude distortion of the input dc voltage to the VSI and has the most significant impact on the spectral errors (difference between theoretical and practical spectra). It is obvious that the sprawling effect of RPWM undoubtedly influenced by input fluctuation and the discrete harmonic clusters may reappear. The influence of dc link fluctuation on harmonics and their spreading effect in the VSI remains invalidated. A case study is done with four different filter capacitor values in this paper and results are compared with the constant dc input operation. This paper also proposes an ingenious RPWM, a ripple dosed sinusoidal reference-random carrier PWM (RDSRRCPWM), which has the innate capacity of suppressing the effect of input fluctuation in the output than the other modern PWM methods. MATLAB based simulation study reveals the fundamental component, total harmonic distortion (THD) and harmonic spread factor (HSF) for various modulation indices. The non-ideal dc link is managed well with the developed RDSRRCPWM applied to the VSI and tested in a proto type VSI using the field programmable gate array (FPGA).

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.129-134
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• 2009

To ensure the safety and functionality of a railroad bridge, maintaining the integrity of the bridge via continuous structural health monitoring is important. However, most structural integrity monitoring methods proposed to date are based on modal responses which require the extracting process and have limited availability. In this paper, the applicability of the existing damage identification method based on free-vibration reponses to time-domain deflection shapes due to moving train load is investigated. Since the proposed method directly utilizes the time-domain responses of the structure due to the moving vehicles, the extracting process for modal responses can be avoided, and the applicability of structural health evaluation can be enhanced. The feasibility of the presented method is verified via a numerical example of a simple plate girder bridge.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.1
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• pp.37-46
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• 2017

Thermal Marangoni flow has been observed inside droplets on heated surfaces, finally resulting in a coffee stain effect. This study aims to visualize and control the thermal Marangoni flow by employing periodic vertical vibration. The variations in the contact angle and internal volume of the droplet as it evaporates is observed by using a combination of continuous light and a still camera. With regard to the internal velocity, the particle image velocimetry system is applied to visualize the internal thermal Marangoni flow. In order to estimate the internal temperature gradient and surface tension on the surface of a droplet, the theoretical model based on the conduction and convection theory of heat transfer is applied. Thus, the internal velocity increases with an increase in plate temperature. The flow directions of the Marangoni and gravitational flows are opposite, and hence, it may be possible to control the coffee stain effect.