• Proceedings of the Korea Concrete Institute Conference
• /
• 2003.05a
• /
• pp.834-839
• /
• 2003

Previous research has been conducted on an ultrasonic wave reflection method that utilizes a steel plate embedded in the concrete to measure the reflection loss of shear waves at the steel-concrete interface. The reflection loss has been shown to have a linear relationship to compressive strength at early ages. The presented investigations continue this research by examining the fundamental relationship between the reflection loss, measured with shear waves, and the hydration kinetics of Portland cement mortar, represented by dynamic elastic moduli, compressive strength and degree of hydration. Dynamic elastic moduli are measured by fundamental resonant frequency and degree of hydration is determined by thermogravimetric analysis. The water/cement ratio was varied for the tested mixture compositions. The results presented herein show that compressive strength, dynamic shear modulus and degree of hydration have a linear relationship to the reflection loss for the tested mortars at early ages.

• KIEAE Journal
• /
• v.7 no.3
• /
• pp.63-70
• /
• 2007

It is known that early reflections, their energy and delay times after the arrival of direct sound are important factors for speech intelligibility. In this basis, acoustical parameters like D50 and C80 had been proposed and are widely used for assessing the listening condition of rooms. These parameters are focused on the fraction of the early energy to the total, regardless of the spatial characteristics of the early reflections. This means that all the early reflections, arrived in certain time boundary. from front, behind, down and upside have the same impact on speech intelligibility. From the questionable simplicity, the influence of the direction of early reflections on speech intelligibility is examined in this study. A computer simulation speech intelligibility test, conducted for 22 university students, found that the reflection of vertical direction with method of the Paired comparison also the preference of 0.746 degree was visible an increase.

• The Korean Journal of Community Living Science
• /
• v.24 no.3
• /
• pp.301-312
• /
• 2013

The purpose of this study was to investigate the differences between attentional networks according to sex and reflection-impulsivity in the cognitive styles of young children. The subjects of the study were 78 5-year-old children from the kindergarten or daycare center in Busan(with 40 in the reflection group, and 38 in the impulsivity group). The tests were conducted by using the Mating Familiar Test and the Attentional Network Test for young children. The study has used two independent t-tests to find out the differences between attentional networks according to sex, and reflection-impulsivity in the cognitive styles of young children. The results of this study were as follows. First, the boys with reflection cognitive style were significantly slower than the girls with the same style(t=2.18, p<.05). Second, young children with reflection cognitive style were significantly faster in the case of alerting effects than those with impulsivity cognitive style(t=-2.53, p<.05). The young children with reflection cognitive style were slower than those with impulsivity cognitive style in the case of orienting effect(t=2.04, p<.05). Children with a combination of both conflict effect and reflection cognitive style were significantly faster than those with impulsivity cognitive style(t=-2.89, p<.01). The results of the study suggested that there was a difference between attentional networks according to sex and reflection-impulsivity cognitive styles of young children.

• Korean Journal of Child Studies
• /
• v.33 no.6
• /
• pp.207-225
• /
• 2012

This study examined the meanings of reflective utterances fathers regarding their paternal role and the relationship of this to the process of a reflective parent education program for fathers whose children had been referred to psychotherapy. The subjects were 2 fathers aged in their late-thirties of 2 children with emotional behavioral problems. The father education program consisted of contents based on object relation theory. The reflective dialogues between fathers and the parent educator in the process of the program were analyzed. The meanings of the reflective utterances made by the fathers were indicated to be the understanding of the relationship between child's problematic behaviors and family dynamics, a reflection on their oppressive child rearing behaviors, the awareness of the necessity for emotional exchange with family members, the importance of cooperation between both the mother and father when it comes to child rearing, and the values at the heart of being together with children. The implications of the results were also discussed.

• Journal of the Korean Institute of Educational Facilities
• /
• v.20 no.1
• /
• pp.37-44
• /
• 2013

The present study examines the effects of periodic type diffusers for producing the preferred acoustics for speech and determines the more successful configurations of sound-absorbing and diffusing treatments for achieving good acoustics in classrooms. The measurements were carried out in a 1/10 scale model classroom systematically adding diffusers to one or more of four surfaces of the room. A total of 13 combination of diffusers with absorptive treatments were investigated. Adding diffusers on the ceiling were more effective to increasing the early-arriving reflection energy($G_{50}$) than adding absorptive materials on the entire ceiling. The late arriving reflection energy($G_{late}$) was decreased with increasing amounts of diffusing treatments of upper front or rear wall and this resulted in achieving higher early-to-late ratios($G_{50}$). Adding diffusers on the upper front wall($AC_{100}DUFW_{26}$) achieved more uniform acoustical conditions over the receiver positions than adding diffusers on the upper rear wall($AC_{100}DUFW_{26}$). Adding diffusers on the ceiling and absorptive materials on the lower front wall($AC_{75}DC_{25}ALFW_{26}$) achieved better acoustical conditions than adding the absorptive materials on the entire ceiling and lower front wall($AC_{100}ALFW_{26}$).

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.14 no.11
• /
• pp.5559-5569
• /
• 2013

The purpose of this study was to examine the effect of the reflection rubric on frequency and content of critical thinking in CSCA. The researcher carried out research during 4 weeks, on 60 students taking the course of 'educational methods and educational technology' in K collage. As the result of this study, The reflection rubric frequency could not be significant difference in critical thinking, but could be significant difference in critical thinking content and collaboration argumentation. The reflection rubric could prevent learner form giving one side reasoning, considered both side opinion and grounds. Also the reflection rubric could trigger learner to construct collaborative knowledge building more strongly. This study showed that the reflection rubric have significant impacts on the argumentation collaboration learning in CSCA.

• Proceedings of the Acoustical Society of Korea Conference
• /
• spring
• /
• pp.439-442
• /
• 2000

When we measure the acoustical properties of a room using multiple microphone system, it is important to grasp exact time delay of the early reflections from impulse response pair. But it is often very difficult to identify the early reflections in natural shape, because a waveform may be deformed due to the characteristics of a sound source loudspeaker, microphone and reflected wall and overlapping of plural waveform. In this paper to obtain more accurate and enough early reflections, we propose the brand-new five-channel sound receiving system and introduce peak-detecting algorithm. The system has microphones mounted at the origin and four points of a regular tetrahedron. The newly introduced peak-detecting algorithm can show exact peak position in each channel, in spite of deformation due to reflected walls, loudspeaker and microphone.

• Smart Structures and Systems
• /
• v.32 no.4
• /
• pp.253-266
• /
• 2023

The time-reversal method is employed to improve the ability of pipeline defect detection, and a new approach of identifying the pipeline defect depth is proposed in this research. When the L(0,2) mode ultrasonic guided wave excited through a lead zirconate titinate (PZT) transduce array propagates along the pipeline with a defect, it will interact with the defect and be partially converted to flexural F(n, m) modes and longitudinal L(0,1) mode. Using a receiving PZT array attached axisymmetrically around the pipeline, the L(0,2) reflection signal as well as the mode conversion signals at the defect are obtained. An appropriate rectangle window is used to intercept the L(0,2) reflection signal and the mode conversion signals from the obtained direct detection signals. The intercepted signals are time reversed and re-excited in the pipeline again, result in the guided wave energy focusing on the pipeline defect, the L(0,2) reflection and the L(0,1) mode conversion signals being enhanced to a higher level, especially for the small defect in the early crack stage. Besides the L(0,2) reflection signal, the L(0,1) mode conversion signal also contains useful pipeline defect information. It is possible to identify the pipeline defect depth by monitoring the variation trend of L(0,2) and L(0,1) reflection coefficients. The finite element method (FEM) simulation and experiment results are given in the paper, the enhancement of pipeline defect reflection signals by time-reversal method is obvious, and the way to identify pipeline defect depth is demonstrated to be effective.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.18 no.5
• /
• pp.727-738
• /
• 1994

It has been representing the delicate changes which express new sentiments through the floating, fluid, free look with the transparent, sheer material in fashion during the early 1990's. The concept of lightness is selected to describe the phenomenon of recent fashion. The purpose of this study is to identify the distinctive characteristics of lightness as external forms and internal meaning in fashion of the early 1990's. The data were collected from fashion magazines such as American Vogue, Italian Vogue from 1987 to 1994. The characteristics of lightness of fashion in the early 1990's are as follows; The external forms are consisted of the material such as the transparent, sheer, soft material, of slim and bell silhouette which occupying the more space in bottom, of the drapery, pleats to shape the unfitted look and is identified as the open, whole, indeterminate and planar intergration form according to the category of clothing form suggested by Belong. It is also the reflection of the social changes which is getting out of the modernity. It is the results of the dominant social state which are diffused the sensual pleasures, transitoriness.

• Proceedings of the KSR Conference
• /
• 2004.10a
• /
• pp.1353-1359
• /
• 2004

There are many massive components added on the railway overhead-line. These components cause larger fluctuations of contact forces, which are due to wave reflections and Doppler effects when a high-speed train passes those. In this paper, mathematical formula are derived for the relation between the added mass and contact force fluctuations. Using the derived formula, we calculate a added mass on the overhead-line which cause amplification factor to become 2.5. German design practice requires that amplification factor due to the wave reflection should be less than 2.5 to obtain good current collection performance. To show the validity of the formula, simulation results are compared with the calculation results. Simulation results showed that contact force fluctuations grow rapidly when an added mass is larger than the calculation result. Therefore, the simple form of formula can be used for estimating maximum added mass not to cause large fluctuations of contact forces in early design phase.