• 한국전산유체공학회:학술대회논문집
• /
• 2010.05a
• /
• pp.352-357
• /
• 2010

A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcaiton) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.

• Journal of computational fluids engineering
• /
• v.15 no.3
• /
• pp.54-59
• /
• 2010

A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcation) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow, including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.

• Journal of the Korean Institute of Telematics and Electronics S
• /
• v.35S no.3
• /
• pp.93-101
• /
• 1998

In Integrated Tube Components(ITC) process in themanufacturing of color display tube, we describe the necessity of the convergence measurement method using photo sensors. Compared with methods using 1D or 2D cameras, its characteristics is to use of moving image patterns and fixed sensors. This measurement method is formulated as the measurement problem of the phase difference in phase changing periodic signals. The convergence measurement system using photo sensors, for the good performance, must have a small standard deviation for the repetitive measurement in the same condition and a fast measurement time for thecovergence change. By above two conditions, we proposed the real time measurement algorithm of the pahse difference using fundametal and harmonic in phase changing periodic signals. And, the proposed algorithm is applied to the convergence measurement system.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.26 no.9
• /
• pp.1436-1443
• /
• 1989

In this paper, we propose a maximum-likelihood estimation(MLE) method to obtain the location and the amplitude of the pulses in MPE( multi-pulse excitation)-LPC speech synthesis using multi-pulses as excitation source. This MLE method computes the value maximizing the likelihood function with respect to unknown parameters(amplitude and position of the pulses) for the observed data sequence. Thus in the case of overlapped pulses, the method is equivalent to Ozawa's crosscorrelation method, resulting in equal amount of computation and sound quality with the cross-correlation method. We show by computer simulation: the multi-pulses obtained by MLE method are(1) pseudo-periodic in pitch in the case of voicde sound, (2) the pulses are random for unvoiced sound, (3) the pulses change from random to periodic in the interval where the original speech signal changes from unvoiced to voiced. Short time power specta of original speech and syunthesized speech obtained by using multi-pulses as excitation source are quite similar to each other at the formants.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.3
• /
• pp.195-198
• /
• 2014

In this paper, a measurement method to obtain the optical properties of a liquid base on a side-polished single mode fiber was proposed and demonstrated. The device showed periodic resonance coupling against wavelengths. The refractive index and dispersion characteristics of a liquid were calculated by use of the spacings of periodic resonance wavelengths of the device. The thermo-optic coefficient of the liquid was obtained by monitering the shift of resonance wavelengths of the devices with change of environmental temperature.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.222.2-222.2
• /
• 2015

A $Ge_2Sb_2Te_5$ nanowire (GST NW) phase change memory device is investigated with Joule heating electrodes. GST is the most promising phase change materials, thus has been studied for decades but atomic structure transition in the phase-change area of single crystalline phase-change material has not been clearly investigated. We fabricated a phase change memory (PCM) device consisting of GST NWs connected with WN electrodes. The GST NW has switching performance with the reset/set resistance ratio above $10^3$. We directly observed the changes in atomic structure between the ordered hexagonal close packed (HCP) structure and disordered amorphous phase of a reset-stop GST NW with cross-sectional STEM analysis. Amorphous areas are detected at the center of NW and side areas adjacent to heating electrodes. Direct imaging of phase change area verified the atomic structure transition from the migration and disordering of Ge and Sb atoms. Even with the repeated phase transitions, periodic arrangement of Te atoms is not significantly changed, thus acting as a template for recrystallization. This result provides a novel understanding on the phase-change mechanism in single crystalline phase-change materials.

• Research in Community and Public Health Nursing
• /
• v.7 no.2
• /
• pp.410-419
• /
• 1996

This study was reviewed from 1000 articles related to family planning from 1970 to 1990 and 20 articles associated with natural family planning from 1980 until the present. The purpose of natural family planning(NFP) is to identify the time ovulation of women themselves, to have intercourse with periodic abstinence, and to deliver a healthy child. The ultimate goal of NFP is to promote the family's health. The NFP method is described as periodic abstinence of intercourse to avoid pregnancy by identifying the ovulation time in the menstration cycle. Clinical symptoms and signs of reflection underlying changes in Estrogen and Progesterone are the change of basal body temperature, the change of cervical mucus and cervix, abdominal pain and breast tenderness. The types of NFP are the calender rthythm method, basal body temperature methods, cervical mucus method, symptothermal method, cyclo-thermal method and home based ovulation test kits. Recently the cyclo-thermal method involved. It is calendar rhythm method applied to B.B.T. For the cervical mucus method, when the estrogen level in the blood concentration is increased, the mucus begins to excrete, the amount of moist mucus increases while the mucus is clear, slippery, and smooth. For 3 days, this timing can be considered contraception. Fertility is at a maximum on the day mucus appears, abstinence for 3 days is a type of contraception. Sexual intercourse on a maximum day of mucus maximizes pregnancy potential. But, the contraception depends on the practice of a perfect rule. For basal body temperature methods, at ovulation time, the temperature increases $0.2^{\circ}C-0.5^{\circ}C$. Through the review of literature a high temperature above $0.2^{\circ}C$ for 3 days indicates that the previous 6 day period was ovulation and fertilization. The Symptothermal method is used to determine the prediction of ovulation through the observation of mucus excretion, high temperature, the change of cervical mucus, low abdominal pain, vaginal discharge, and breast change. Home based ovulation test kits are cervico-vaginal fluid aspiration, test a digital electric thermometer, body fluid(blood, saliva, urine) test kits, They are on the market. However, research on the contraception method is still in progress. For pregnancy it is still too early to use home based ovulation test kits because of deficit of reliability and simplicity more research on the technology is needed. It is suggested that NFP methods be included in nursing curriculum in order to educate NFP users how to effectively use NFP methods. Furthermore, this study has implications for the dissemination of NFP methods in terms of Korean policies of family planning and the support of community welfare agences.

• Journal of Korean Biological Nursing Science
• /
• v.15 no.3
• /
• pp.122-132
• /
• 2013

Purpose: The purpose of this study was to evaluate the effect of periodic video education on knowledge about hemodialysis, patient role behavior and the physiologic index in patients with hemodialysis. Methods: One-group pretest-posttest design was applied. A total of 50 patients with hemodialysis at a university hospital hemodialysis unit in Daegu participated. Periodic video education about kidney function, diet, arteriovenous fistula management, medication, and exercise was administered to them for 12 weeks at intervals of 2 weeks. Before and after the education, the participants completed the self-administered questionnaires of knowledge about hemodialysis and patient role behavior and the measures of serum potassium and phosphorus concentration, weight gain between hemodialysis sessions, and adequacy of dialysis (Kt/V). Statistical analysis was performed using paired t-test. Results: Knowledge about hemodialysis and patient role behavior were significantly different between before and after education (p<.01). For the physiologic index, serum potassium concentration and weight gain between hemodialysis sessions were not significantly different but the serum phosphorus concentration and Kt/V were significantly different between before and after education (p<.05). Conclusion: The results suggest that the periodic video education for patients with hemodialysis contributed to the change and improvement in knowledge about hemodialysis, patient role behavior, and the physiologic index.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.29 no.7
• /
• pp.540-549
• /
• 2018

Classifying the front body of the missile and debris of a high-speed missile in intercepting a high-speed missile is an important issue. The motion of the front body of the missile is characterized by precession, but the motion of the debris in the boosting part separation phase is characterized by tumbling. There are periodic patterns caused by the precession or tumbling motion on the dynamic radar cross section (RCS). In addition, there are statistical properties caused by the change pattern of the dynamic RCS. A method is proposed to classify the front body of the missile and debris using periodic and statistical properties of the dynamic RCS. Three kinds of feature vector are extracted from the periodic and statistical properties of the dynamic RCS. The front body of the missiles and debris was classified using a support vector machine.

• Korean Journal of Remote Sensing
• /
• v.35 no.4
• /
• pp.573-587
• /
• 2019

A multi-temporal approach using remotely sensed time series data obtained over multiple years is a very useful method for monitoring land covers and land-cover changes. While spectral-based methods at any particular time limits the application utility due to instability of the quality of data obtained at that time, the approach based on the temporal profile can produce more accurate results since data is analyzed from a long-term perspective rather than on one point in time. In this study, a multi-temporal approach applying a multi-periodic harmonic model is proposed for classification of remotely sensed data. A harmonic model characterizes the seasonal variation of a time series by four parameters: average level, frequency, phase, and amplitude. The availability of high-quality data is very important for multi-temporal analysis.An satellite image usually have many unobserved data and bad-quality data due to the influence of observation environment and sensing system, which impede the analysis and might possibly produce inaccurate results. Harmonic analysis is also very useful for real-time data reconstruction. Multi-periodic harmonic model is applied to the reconstructed data to classify land covers and monitor land-cover change by tracking the temporal profiles. The proposed method is tested with the MODIS and GOCI NDVI time series over the Korean Peninsula for 5 years from 2012 to 2016. The results show that the multi-periodic harmonic model has a great potential for classification of land-cover types and monitoring of land-cover changes through characterizing annual temporal dynamics.