• Journal of the Korean Society for Railway
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• v.17 no.1
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• pp.7-13
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• 2014

Stiffness variations and wave propagation/reflection in railway catenaries are the primary sources of contact loss between a pantograph and a railway contact wire. This paper analyzes which design parameter is more important for 200km/h conventional rail and 300km/h high-speed rail, in order to effectively reduce the contact loss. For the high-speed rail, the wave propagation and reflection in the overhead contact lines are more influential than the stiffness variation over a span. When the high-speed rail needs to speed-up, it is necessary to develop higher strength contact wires in order to increase the wave propagation speed. In addition, the dropper clamp mass should be reduced in order to alleviate the wave reflection. However, it is noted that the increase in the tension to a messenger wire could deteriorate the current collection quality, which contrasts with expectations. For the 200km/h conventional rail, the stiffness variation over a span is more influential than the wave propagation and reflection. Therefore, shortening span length, increasing the tension in the contact wire and optimizing the location of the droppers are recommended for a smoother stiffness variation over the span.

• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.78-84
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• 2008

Recent earthquakes near nuclear power plants in Korea have triggered public concerns about possible seismicity of the Ulsan Fault Zone in the south-eastern part of the Korean peninsula. To reveal subsurface structures of this fault zone, we conducted high-resolution seismic refraction and reflection surveys, and closely spaced gravity measurements in the Dongchon River valley north of Ulsan, Korea. Here alluvium covers the north-south trending fault zone in a 1-km wide valley. Both source points and receivers were spaced at 5-m intervals for the 24-channel seismic refraction and reflection methods, along two profiles of 835 m and 415 m length. Gravity data were also measured along these profiles at 131 stations using a 10-m interval. Synergetic interpretation of seismic refraction, high-resolution seismic reflection, and gravity surveys across the valley indicates that the Ulsan Fault Zone was formed by apparent north-south strike-slip motions during the Cretaceous, and that some faults may have been reactivated by east-west compressional or transpressional stresses during the Tertiary or Quaternary.

• Journal of the Korean Institute of Telematics and Electronics
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• v.11 no.1
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• pp.1-7
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• 1974

This paper discribes the reflector type ultrasonic concentrator which makes hghintencity of ultrasonic field. This was made by rotating parabolic surface which only using total reflection aria, that makes boundary by the critical angle of reflection of sound. I made two binds of concentrator acording to the type of ultrasonic transduser: one is internal surface reflector type concentrator, which is available for disc type transducer, and the other is external surface reflector type concentrator which is available cylinderical transduser. In the mony aspects the reflector tripe concentrator is supel'ier to the reflection type concentrator as plastics lens; It is more durable in high temperature and high intencity ultrasonicfield then refrector type concentrator because of it is made by glass or metal, and it has higher. efficiency because of it wasts made by only total reflection aria that is without absoption lose. I think this is useful ultrasonic concentrator in mony industrial field, in which high intencitr of ultrasonic energy was used.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.4121-4124
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• 2015

Near infrared blocking function in energy saving window glass is required. The design, deposition and characteristics of optical thin films for reflection of near-infrared light were studied. The optical thin film is designed as laminated film structure with low refractive index film and high index film. Deposition experiments of $SiO_2$ and $TiO_2$ thin films with designed structure using the RF sputtering method were carried out. The characteristics of the thin film with deposition conditions were analyzed. High-refractive-index thin film of $TiO_2$/low refractive-index thin film of $SiO_2$ and high-refractive-index thin film of $TiO_2$ structure for reflection of near-infrared light was designed to be simulated. Results of simulation showed reflectance of 30% or more in the range from 930nm to 1682nm. Triple layer thin films fabricated with simulated results showed wavelength bands from 930nm to 1525nm for the reflectance of 33% or more.

• Journal of Science Education
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• v.44 no.2
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• pp.225-239
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• 2020

This study aims to analyze the characteristics of reflective thoughts of students during experiments in general physics experiments. The participants were 32 college students, they submitted 10 experiment reports including answers to questions for reflective thinking. The results were as follows: First, students show reflective thinking broadly in the experiment, levels were followed by practical reflection, technical reflection, and critical reflection. Also, they actively accepted the knowledge related to experiments, but were passive in connecting new knowledge and experiences obtained through the experiments or forming new questions. Second, the reflective thinking of students show high correlation with experiments related to prior knowledge or the easy-to-understand process. Third, through the qualitative analysis of open-ended questions, it was confirmed that technical reflection occurs in individual evaluation, practical reflection in group evaluation, and practical reflection and critical reflection in improvement proposal. While the students' reflective thinking were superficial or mainly functional, however, they recursively examined the learning contents and the experimental process concurrently.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.317-327
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• 2013

Air pollution and artificial heat of urban areas have caused the urban heat island in which asphalt pavements absorb solar heat during the daytime and release the heat at night. Hence, in order to improve the environment of urban areas, it is necessary to examine cooling pavements that can reduce heat on road pavements in urban areas. The application of temperature insulation paints on road pavements require to reduce black brightness for visibility, to increase the reflection rate of infrared light and minimize the reflection rate of visible light. In the study, one part of Acrylic-emulsion was used as a main binder, and the changes in black brightness and the changes of addition ratio (0%, 15%, 30%) of hollow ceramics, as well as kinds of paints (carbon black pigment, mixed mineral pigment) were selected as the main experimental factors. The performance of temperature reduction of cooling pavements was analyzed through the reflection rate of spectrum, the reflection rate of solar heat, and the lamp test. Abrasion resistance, UV accelerated weather resistance, and sliding resistance were tested in real situations. In addition, the performance of heat reduction of testing pavements covered with high-reflection paints was analyzed by using an infrared camera. As the test results, when using mixed mineral paints and hollow ceramic of 30%, the reflection rate of spectrum was 43% in the area of near-infrared ray and 17% in the area of visible light at black brightness of $L^*$=42.89 and the reflection rate of solar heat was 27.5%. Total color difference was ${\Delta}E$=0.27 in the test of UV Accelerated Weather Resistance, indicating almost no changes in color. BPN was more than 53 when scattering #2 and #4 silica sand of more than $0.12kg/m^2$. In Taber's abrasion resistance test, abrasion loss was up to 86.4mg at 500 rotations. The performance of heat reduction was evaluated using an infrared camera at the test section applying high-reflection paints to asphalt pavements, in which the results showed that the temperature was reduced by $12.7^{\circ}C$ on CI-30-40 cooling pavements ($L^*$=38.76) and by $14.2^{\circ}C$ on CI-30-60 cooling pavements ($L^*$=57.12).

• The Journal of the Korea institute of electronic communication sciences
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• v.3 no.1
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• pp.12-18
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• 2008

In this research, we proposed a method for high precision measurement than laser displacement measurement. The proposed method finds the causes of error due to change in reflected laser signal level reflected from an object and compensation, and we designed this by applying laser displacement meter.

• Electrical & Electronic Materials
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• v.9 no.5
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• pp.498-505
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• 1996

In the present work, we have developed the simulator to optimize the process conditions of the AR(antireflection) and HR(high-reflection) coatings for the high power laser diode. The simulator can run on the PC. After making the simple optical model, we establish the Maxwell equations for the model by the operator conversion. By using the Mathematica, we derive a matrix for the multilayer system by applying the equations to the model and optimize the AR and HR coating process conditions by obtaining the reflection rate from the matrix. We also prove the validity of the simulator by comparing the simulation with the characteristics of the laser diode which is AR and HR coated according to the optimized conditions.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.19-26
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• 2009

This study is performed by method for the influx of natural light in underground space. to solve the several negative underground issues make the covered courtyard and high reflected wall toward the adjacent space. for illuminance level test of sunken garden space, the adjacent space size is $15M{\times}9M{\times}12M$ sunken Garden with space to install the ceiling on the size of the companion light performance analysis, and seasonal changes derived by the light of changes in performance. In addition, increase the distance of the wall and the adjacent space and estimate the average at true time P.M12. The resulting data indicate that the road was an average lux DESKTOP RADIANCE of the modeling and analysis was conducted.

• ETRI Journal
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• v.24 no.5
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• pp.341-348
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• 2002

We propose an asymmetric sampled grating laser and a multi-wavelength laser array associated with it. Asymmetric sampling periods combined with an index shifter make it possible to use first order reflection for lasing operations. With the structure of our design, we achieved a simple fabrication procedure as well as a high yield without using complex and time-consuming e-beam lithography for multi-period gratings. We analyzed the effect of mirror coating by numerical analysis to improve single mode and power extraction performance. By using high reflection-antireflection coatings, we obtained high power extraction efficiency without degradation of the single mode property. For the multi-wavelength laser array, to gain wavelength control, we varied the sampling periods from one laser to an adjacent laser across the array. With this approach, we showed the feasibility of an array of up to 30 channels with 100 GHz wavelength spacing.