• Journal of Sensor Science and Technology
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• v.27 no.6
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• pp.421-426
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• 2018

To develop a piezoelectric inkjet printhead for high-resolution and high-speed printing, we studied the characteristics of an inkjet printhead by analyzing the major design parameters. An analytical model for the inkjet printhead was established, and numerical analysis of the coupled first-order differential equation for the defined state variables was performed using state equations. To design the dimension of the inkjet printhead with a driving frequency of 100 kHz, the characteristics of the flow rate and discharge pressure of the nozzle were analyzed with respect to design variables of the flow chamber, effective sound wave velocity, driving voltage, and voltage waveform. It was predicted that the change in the height of the flow chamber does not significantly affect the Helmholtz resonance frequency and discharge speed of the nozzle. From the analysis of change in flow chamber width, it is observed that as the width of the flow chamber increases, the ejection speed greatly increases and the Helmholtz resonance frequency decreases considerably, thereby substantially affecting the performance of the inkjet printhead.

• Journal of Biomedical Engineering Research
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• v.16 no.2
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• pp.183-190
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• 1995

The use of ultrasound pulsed Doppler systems has become increasingly popular due to the advantages of easy measurements of blood velocity, volume blood blow, and irregularities of the circulatory system. However, the 2-D Doppler systems have several problems, such as range ambiguity, low signal to noise ratio, and slow frame rate. The mean frequency aliasing problem originating from the pulse repetition frequency is one of major limitations in pulsed Doppler systems. A conventional approach to resolve this problem is tracking the mean frequency close to and beyond the Nyquist frequency along the temporal axis. In this paper, a new concept of tracking the mean frequency along the spatial axis is proposed. The proposed technique is fault tolerant by nature and more suitable for multi gate and 2-D Doppler system than conventional methods.

• Science of Emotion and Sensibility
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• v.14 no.2
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• pp.207-220
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• 2011

The purpose of this study is to investigate sensibility words related with eco-friendly in the two media fashion magazines and internet newspapers and to analysis their appearance frequency and changes by the year through 1999~2010. Most frequently used words are 'nature, eco, cotton, natural fiber, health, fresh, clear, preservation, harmony, com fiber, and Lohas'. The words are divided in 4 groups: 'Nature/Environment, Material/Fiber, Human, and Adjectives/Micell'. A point of appearing time is analyzed: 'ecology, memory-shape material, organic, spa' were used before 2000, 'nature environment, eco-friendly, stretch material, wellbeing, substitute, recycling' were in 2000-2001, 'smart material, eco material, green' in 2002-2003, 'coolbiz, Lohas, natural dye' in 2004-2005, 'herb medicine, sustainable, warmbiz' in 2006-2007, 'greensumer, greenlife, solar energy, forest bath' in 2008-2009. Looking into their changes, in early 2000, the words of eco-friendly emotion and sensibility had appeared frequently relatively, but later on they decreased, and again recently increased showing highest appearing frequency. 'Nature/Environment' words have appeared recently very much, while 'Human' sensibility words have not changed much or decreased a little. 'Adjective/Micell' words has increased little bit recently. 'Material/Fiber' words showed decrease at fashion magazine, while they increased at the pages of internet news.

• Journal of Science Education
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• v.39 no.2
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• pp.221-238
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• 2015

The purpose of this study was to analyze the introduced contents and the nature of science on the history of science in elementary school science textbooks according to the 2009 revised curriculum. For this purpose, first of all, the frequency of contents of history of science in 8 kinds of science textbooks in elementary school is analyzed by grade cluster and content part. Analysis framework for analyzing the introduced contents on the history of science was characterized with three-dimensional combination of the context, the role and the types(Park, Lee, & Lee, 2011). Analysis framework for the nature of science on the history of science was developed by Leite(2002) and revised by Choi (2005) and Kim(2010) and complemented under one expert in science education. The results of this study are as follows: First, the frequency of contents of history of science in textbook is 26 and it were not equally distributed into science textbooks in elementary school as a result of the analysis by grade cluster and content part. Second, with three-dimensional combination framework only 13 kinds were used in all 48 different types through analyzing the textbooks. It implies that ways of introducing contents of history of science into textbooks were limited to certain types. Third, the nature elements of science were not equally distributed on the history of science in elementary school science textbooks. In conclusion, in order to understand the nature of science through the history of science and to foster scientific literacy ultimately, it implicates that it is need to present various kinds of the history of science for one theme in consideration about the grade cluster and content part. Also more multilateral approach is need to introduce equally distributed into textbooks to reflect the elements of the nature of science.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.47 no.4
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• pp.177-186
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• 2015

Until Mandelbrot introduced the concept of fractal geometry and fractal dimension in early 1970s, it has been generally considered that the geometry of nature should be too complex and irregular to describe analytically or mathematically. Here fractal dimension indicates a non-integer number such as 0.5, 1.5, or 2.5 instead of only integers used in the traditional Euclidean geometry, i.e., 0 for point, 1 for line, 2 for area, and 3 for volume. Since his pioneering work on fractal geometry, the geometry of nature has been found fractal. Mandelbrot introduced the concept of fractal geometry. For example, fractal geometry has been found in mountains, coastlines, clouds, lightning, earthquakes, turbulence, trees and plants. Even human organs are found to be fractal. This suggests that the fractal geometry should be the law for Nature rather than the exception. Fractal geometry has a hierarchical structure consisting of the elements having the same shape, but the different sizes from the largest to the smallest. Thus, fractal geometry can be characterized by the similarity and hierarchical structure. A process requires driving energy to proceed. Otherwise, the process would stop. A hierarchical structure is considered ideal to generate such driving force. This explains why natural process or phenomena such as lightning, thunderstorm, earth quakes, and turbulence has fractal geometry. It would not be surprising to find that even the human organs such as the brain, the lung, and the circulatory system have fractal geometry. Until now, a normal frequency distribution (or Gaussian frequency distribution) has been commonly used to describe frequencies of an object. However, a log-normal frequency distribution has been most frequently found in natural phenomena and chemical processes such as corrosion and coagulation. It can be mathematically shown that if an object has a log-normal frequency distribution, it has fractal geometry. In other words, these two go hand in hand. Lastly, applying fractal principles is discussed, focusing on pulp and paper industry. The principles should be applicable to characterizing surface roughness, particle size distributions, and formation. They should be also applicable to wet-end chemistry for ideal mixing, felt and fabric design for papermaking process, dewatering, drying, creping, and post-converting such as laminating, embossing, and printing.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.2
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• pp.114-121
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• 2010

As a vehicle speed increases, more vibration energy is transmitted from chassis to a driver. Current isolation system for the driver's seat by damping control can reduce the transmitted vibration energy near resonance area. But in higher frequency region than natural frequency multiplied by $\sqrt{2}$, the vibration energy transmitted to the driver has a tendency to be increased. Therefore, the method by natural frequency reduction of the system is preferred to increase the effectiveness of the anti-vibration. However, the natural frequency could not be freely reduced due to the nature of the isolation system structure. A new passive suspension system to reduce the natural frequency is proposed. The theoretical analysis and experimental results show better vibration attenuation compared with the current isolation system.

• Journal of Communications and Networks
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• v.9 no.4
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• pp.482-489
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• 2007

In this paper, two frequency domain signal processing techniques for pulse shape modulation(PSM) ultra wideband(UWB) systems are presented. Firstly, orthogonal detection of UWB PSM Hermite pulses in frequency domain is addressed. It is important because time domain detection by correlation-based receivers is severely degraded by many sources of distortion. Pulse-shape, the information conveying signal characteristic, is deformed by AWGN and shape-destructive addition of multiple paths from the propagation channel. Additionally, because of the short nature of UWB pulses, timing mismatches and synchronism degrade the performance of PSM UWB communication systems. In this paper, frequency domain orthogonality of the Hermite pulses is exploited to propose an alternative detection method, which makes possible efficient detection of PSM in dense multipath channel environments. Secondly, a ranging method employing the Cepstrum algorithm is proposed. This method is partly processed in the frequency domain and can be implemented without additional hardware complexity in the terminal.

• Journal of the Korean Society of Earth Science Education
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• v.16 no.1
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• pp.30-42
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• 2023

The purpose of this study is to quantitatively and qualitatively analyze the science journals written by pre-service elementary school teachers, and to categorize the view on the nature of science and the process of their change. For this purpose, 112 science journals written by 13 pre-service elementary school teachers were analyzed. The frequency of each area was analyzed using the research framework of the four areas of the nature of science, and the pattern of change in perspective on the nature of science was inductively derived and classified using the VNOS-C test analysis framework. As a result, The nature of scientific thinking, nature of scientific knowledge, nature of STS, and nature of scientific inquiry were described in relatively similar proportions, but among them, The nature of scientific thinking appeared in the largest percentage, and the nature of scientific inquiry was described in the smallest percentage. The variability of scientific knowledge, the importance of empirical evidence, and the positive and negative effects of science were especially intensively addressed. In addition, the changing aspects of pre-service elementary school teachers' perspectives on the nature of science could be categorized into 'naive view maintenance type', 'informed view maintenance type', 'regression type', 'development type', and 'mixed type'. The element of 'the empirical nature of scientific knowledge' showed various patterns of change depending on the students, and most of the students maintained a informed view on the tentativeness of scientific knowledge for several sessions.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.8 no.1
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• pp.52-62
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• 2005

The objectives of this research is searching for the improvement scheme of spacial use of the Nature Environmental Conservation and its Utilization Facility through the analysis of those existing facilities from the structural and operational view points. In this study, firstly, analysis is commencing with the distinction of lawful and operational concepts of Nature Environmental Conservation and its Utilization Facility. In law, the concept is defined as an individual facility, while practical use of the concept has been understood as a collective space itself. Secondly, frequency tables in regard to the duration of the construction, types of location and objectives, and facility numbers are prepared on the basis of 53 cases of completed and under construction facilities. Conclusively, through the comparisons of facilities of Korea, United Kingdom and Germany, the future considerations on the improvement of the facilities in light of structural and operational aspects has been recommended. In structural view, ecological conservation aspect should be considered from the planning stage of the facility. And at the operational stage, various considerations should be given to the employment of facility experts and development of educational programs respectively.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.27 no.2
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• pp.29-42
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• 2024

As a global response to climate and biodiversity challenges, there is an emphasis on the conservation and restoration of ecosystems that can simultaneously reduce carbon emissions and enhance biodiversity. This study comprised a text analysis and keyword extraction of 1,100 research papers addressing nature restoration in Korea, aiming to provide a quantative and systematic evaluation of domestic research trends in this field. To discern the major research topics of these papers, topic modeling was applied and correlations were established through network analysis. Research on nature restoration exhibited a mainly upward trend in 2002-2022 but with a slight recent decline. The most common keywords were "species," "forest," and "water". Research topics were broadly classified into (1) predictions of habitat size and species distribution, (2) the conservation and utilization of natural resources in urban areas, (3) ecosystems and landscape managements in protected areas, (4) the planting and growth of vegetation, and (5) habitat formation methods. The number of studies on nature restoration are increasing across various domains in Korea, with each domain experiencing professional development.