• 한국노년학
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• v.40 no.3
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• pp.413-428
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• 2020

The purpose of this study was to analyze the effects of digital literacy and the frequency of contact with children or grandchildren via ICT on cognitive functions of 8,942 adults over age 65 who responded to the 2017 National Survey of Older Koreans, using multiple regression analysis. We found that digital literacy was the most significant factor on cognitive functions of the elderly. Also, the frequency of contact with grandchildren via ICT was a positive factor for cognitive function and had a positive correlation with digital literacy. Based on this results, the importance of digital literacy education and intergenerational communication via ICT were discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.3 s.108
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• pp.255-262
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• 2006

Frequency spectrum using the conventional Fourier analysis gives adequate information about the dynamic characteristics of the slider air bearing for the linear and stationary cases. The intermittent contacts for the extremely low flying height, however, generate nonlinear and nonstationary vibration at the instant of contact. Nonlinear dynamic model should be developed to simulate the impulse response of the air bearing during slider-disk contact. Time-frequency analysis is widely used to investigate the nonstationary signal. Several time-frequency analysis methods are employed and compared for the slider vibration signal caused by the impact against an artificially induced scratch on the disk. The representative Wigner-Ville distribution leads to the severe interference problem by cross terms even though it gives good resolution both in time and frequency. The smoothing process improves the interference problem at the expense of resolution. In order to get the results with good resolution and little interference, the reassignment method is proposed. Among others the reassigned Gabor spectrogram shows the best resolution and readability with negligible interference.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.5
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• pp.282-288
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• 2010

Experiment on the surface characteristics of polymer films treated by atmospheric pressure plasma has been conducted. We chose the process parameters as frequency, gas flow, treatment time, and scrutinized the effects of the process parameters on the surface characteristics of polymer materials by measuring the contact angle and examining SEM. As the result, the surface characteristics highly depends on frequency, reaction gas and treatment time. In the case of PC substrate, the contact angle was changed from $83.5^{\circ}$ (before plasma treatment) to $30^{\circ}$ (after plasma treatment) at 30 kHz, CDA 0.6%, and number of repeat 7. In the case of PET substrate, the contact angle change was found from $59^{\circ}$ to $23.5^{\circ}$ at 20 kHz, CDA 0.6%, and number of repeat 7. In the case of EVA substrate, it shows from $84^{\circ}$ to $44.2^{\circ}$ at 30 kHz, CDA 0.6%, and number of repeat 7.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.5
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• pp.572-577
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• 2011

Curve squealing of inter-city railway vehicle is a noise with high acoustic pressure and rather narrow frequency spectra. This noise turns out to be very annoying for the people living in the neighborhood of locations and the passenger in railway vehicle where this phenomenon occurs. Squealing is caused by a self-exited stick-slip oscillation in the wheel-rail contact. Curve squeal noise of railway vehicles that passed by a factor of the speed limit, so to overcome in order to improve running performance is one of the largest technology. In the present paper, characteristic of squeal noise behavior at the Hanvit-200 tilting train test-site. Curve squealing of railway wheels/rail contact occurs in R400~ R800 curves with a frequency range of about 4~11 kHz. If the curve is less than the radius of wheel frail contact due to |left-right| noise level difference (dBA) shows a significant effect of squeal noise were more likely.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.15 no.2
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• pp.64-72
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• 2001

In this paper, forward Zero Voltage Switching Multi Resonant Converter(ZVS MRC) for non-contact charging energy transmission is reposed. The forward ZVS MRC is effective in adsorbing parasitic element as well as minimizing the switching loss. That can accommodate very high frequency. So forward ZVC MRC is applied to non-contact charging energy transmission. Used converter has saperatable transformer and synchronous rectifiers. Coupling coefficient(k), leakage inductance, coupling inductance and resonant frequency are observed for the air gap. By using the observed value, this circuit is designed and implemented. This proposed circuit is simulated by the PSPICE and experimented. The voltage stress of a main switch and the output power of the converter are measured. This paper show that is compatible for non-contact charging energy transmission.

• Journal of KSNVE
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• v.9 no.4
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• pp.778-784
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• 1999

A method for obtaining the motion of an impact system whose primary and secondary system are composed of lumped masses, springs and dampers, and all the contacts are made through spring and damping elements is presented. The frequency response functions derived from the equations of motion and the impulse response functions obtained from the inverse Fourier transform of the derived frequency response functions are used for the calculation of the system responses. The procedure developed for the calculation of displacements and force time-histories was based on the convolution integrals of impulse response functions and forces applied to the systems. Time histories of displacements and contact forces are obtained for the case where a random excitation is applied to a point in the system. Impact statistics such as contact forces and the time between impacts calculated from those time histories is presented.

• Korean Journal of Materials Research
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• v.19 no.8
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• pp.417-420
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• 2009

This study develops a highly transparent ohmic contact using phosphorus doped ZnO with current spreading for p-GaN to increase the optical output power of nitride-based light-emitting diodes (LEDs). The phosphorus doped ZnO transparent ohmic contact layer was prepared by radio frequency magnetron sputtering with post-deposition annealing. The transmittance of the phosphorus doped ZnO exceeds 90% in the region of 440 nm to 500 nm. The specific contact resistance of the phosphorus doped ZnO on p-GaN was determined to be $7.82{\times}10^{-3}{\Omega}{\cdot}cm^2$ after annealing at $700^{\circ}C$. GaN LED chips with dimensions of $300\times300{\mu}m$ fabricated with the phosphorus doped ZnO transparent ohmic contact were developed and produced a 2.7 V increase in forward voltage under a nominal forward current of 20 mA compared to GaN LED with Ni/Au Ohmic contact. However, the output power increased by 25% at the injection current of 20 mA compared to GaN LED with the Ni/Au contact scheme.

• Journal of Families and Better Life
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• v.34 no.5
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• pp.151-166
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• 2016

This study examined frequency of contact between parents and their non-coresident, never-married daughters and sons compared to children in other marital statuses. Despite an increasing number of never married adults, little is known about the extent to which they may be willing to remain connected to and exchange support with their parents. The data were drawn from first wave of the Korean Longitudinal Study of Ageing (KLoSA, 2006). For analyses, respondents who had at least one non-coresident child aged 40 or older were selected, resulting in the analytic sample of 2,755 parents with 7,741 children. Both sibling fixed effects regression models and regression models with robust standard errors were estimated using the xtreg and reg procedures in STATA. Findings revealed significant marital status by gender interaction effects on face-to-face contact. Never-married daughters were more likely to see their parents compared to their married, divorced, or widowed counterparts. Never-marred sons, on the other hand, reported slightly lower levels of in-person contact with their parents in comparison to married sons and lower levels of contact compared to divorced or widowed sons. More frequent contact via phone, mail, or email was reported in daughter-parent relationship compared to son-parent relationship, but no significant marital status by gender interactions were observed.

• Journal of Preventive Medicine and Public Health
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• v.53 no.2
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• pp.106-116
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• 2020

Objectives: This study aimed to develop a valid social contact survey instrument and to verify its feasibility for use among Korean adults. Methods: The Delphi technique was used to develop an instrument to assess social contacts, which was then applied in a cross-sectional pilot study. A panel of 15 medical professionals reviewed the feasibility and validity of each item. The minimum content validity ratio was 0.49. Thirty participants used the developed measure to record contacts during a 24-hour period. Results: After a systematic review, the survey instrument (parts I and II) was developed. Part I assessed social contact patterns over a 24-hour period, and part II assessed perceptions of contacts in daily life and preventive behaviors (hand hygiene and coughing etiquette). High validity and feasibility were found. In the pilot study, the 30 participants had a combined total of 198 contacts (mean, 6.6 daily contacts per person). The participants' age (p=0.012), occupation (p<0.001), household size (p<0.001), education (p<0.001), personal income (p=0.003), and household income (p<0.001) were significantly associated with the number of contacts. Contacts at home, of long duration, and of daily frequency were relatively likely to be physical. Assortative mixing was observed between individuals in their 20s and 50s. Contact type differed by location, duration, and frequency (p<0.001). Conclusions: The developed social contact survey instrument demonstrated high validity and feasibility, suggesting that it is viable for implementation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.5
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• pp.389-395
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• 2005

The etching technology of the high aspect ratio contact(HARC) is necessary at the critical contact processes of semiconductor devices. Etching the $SiO_{2}$ contact hole with the sub-micron design rule in manufacturing VLSI devices, the unexpected phenomenon of 'profile tilting' or 'bottom distortion' is often observed. This makes a short circuit between neighboring contact holes, which causes to drop seriously the device yield. As the aspect ratio of contact holes increases, the high C/F ratio gases, $C_{4}F_{6}$, $C_{4}F_{8}$ and $C_{5}F_{8}$, become widely used in order to minimize the mask layer loss during the etching process. These gases provide abundant fluorocarbon polymer as well as high selectivity to the mask layer, and the polymer with high sticking yield accumulates at the top-wall of the contact hole. During the etch process, many electrons are accumulated around the asymmetric hole mouth to distort the electric field, and this distorts the ion trajectory arriving at the hole bottom. These ions with the distorted trajectory induce the deformation of the hole bottom, which is called 'profile tilting' or 'bottom distortion'. To prevent this phenomenon, three methods are suggested here. 1) Using lower C/F ratio gases, $CF_{4}$ or $C_{3}F_{8}$, the amount of the Polymer at the hole mouth is reduced to minimize the asymmetry of the hole top. 2) The number of the neighboring holes with equal distance is maximized to get the more symmetry of the oxygen distribution around the hole. 3) The dual frequency plasma source is used to release the excessive charge build-up at the hole mouth. From the suggested methods, we have obtained the nearly circular hole bottom, which Implies that the ion trajectory Incident on the hole bottom is symmetry.