• 센서학회지
• /
• 제27권6호
• /
• pp.421-426
• /
• 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.

• 대한의용생체공학회:의공학회지
• /
• 제16권2호
• /
• pp.183-190
• /
• 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.

• 감성과학
• /
• 제14권2호
• /
• pp.207-220
• /
• 2011

친환경 감성단어를 '환경/자연, 소재/섬유, 인간, 형용사/기타' 등의 4가지 영역으로 분류하고 각 단어에 대하여 그 출현시점, 빈도를 1999~2010년 상반기 간의 인터넷 섬유패션 신문 및 잡지를 중심으로 조사한 결과, 다음과 같은 결론을 얻었다. 가장 빈번히 출현한 단어는 '자연, 환경, 면, 천연섬유, 건강, 신선한, 맑은, 보존, 하모니, 옥수수섬유, 로하스' 등이었다. '친환경' 관련 감성단어의 출현시점을 살펴보면, 2000년도 이전부터 '에코, 형상기억소재, 오가닉, 스파' 등이 사용되어왔으며, 2000-1년도에 '자연환경, 친환경, 스트레치소재, 웰빙의, 대체가능한, 재생가능한' 등이 등장하였다. 2002-3년도에 '스마트소재, 친환경소재, 그린' 등이 사용되기 시작하였고, 2004-5년도에 '쿨비즈, 로하스, 자연염색' 등이 처음으로 사용되었다 2006-7년도에 '한방, 지속가능한, 웜비즈' 등이 사용되었고, 2008-9년도에 '그린슈머, 그린라이프, 태양에너지, 삼림욕' 등이 섬유패션 분야에서 처음 사용되었다. 친환경 감성단어의 출현 양상을 살펴보면, 친환경 감성단어의 출현은 과거 어느 때보다 2008-09년도에 가장 많이 등장하고 있었는데 2000년도 초반에는 비교적 많이 등장하였으나 이후 다소 주춤하였고 이는 근래에 들어 다시 출현빈도가 높아졌다. 영역별로 살펴보면 '환경/자연' 관련 친환경 감성 단어가 과거보다 최근에 두드러지게 빈번히 사용되고 있으며, 이에 비해 '인간' 관련 단어는 주춤하여 약간 감소세이거나 동일한 빈도를 나타내고 있다. 또 '형용사/기타' 관련 단어는 약간 증가세이거나 과거와 동일한 빈도를 나타내고 있었다. '소재/섬유' 관련 단어는 패션잡지에서는 최근에 그 빈도가 줄어드는 경향을 보이는 반면 인터넷 신문에서는 약간 증가하는 추세를 보였다.

• 과학교육연구지
• /
• 제39권2호
• /
• pp.221-238
• /
• 2015

본 연구의 목적은 2009 개정 초등 과학교과서의 과학사 도입 내용과 이에 반영된 과학의 본성 요소를 분석하는 것이다. 분석을 위해 우선 2009 개정 초등 과학교과서 8종을 새롭게 도입된 학년군과 내용 영역에 따라 과학사의 도입 자료와 제시형태를 도출하고 보다 체계적이고 심층적인 분석을 위해 과학사와 관련된 내용을 박세기, 이기영, 이면우(2011)가 개발한 3차원 조합 분석틀을 이용하여 과학사의 도입 내용을 분석하고, Leite(2002)가 개발하고 최윤희(2005)와 정고은(2013)이 수정한 분석틀을 보완하여 과학의 본성 요소를 분석하였다. 이 연구의 분석 결과는 다음과 같다. 첫째, 2009 개정 초등 과학교과서에 제시된 과학사 자료는 총 26개로 학년군 및 내용 영역별로 자료의 분포가 고르지 않았다. 둘째, 전체 48개의 3차원 조합 유형 가운데에서 오직 13개 유형만 사용되고 있어 특정 유형에 편중하여 과학사를 도입하고 있었다. 셋째, 과학사 자료에 반영된 과학의 본성 요소가 학년 및 영역별로 고르게 분포되지 않았다. 결론적으로 과학사를 통해 과학의 본성을 이해하고 과학적 소양을 함양하기 위해서는 2009 개정 초등 과학교과서에서의 학년군과 내용 영역을 고려하여 다양한 유형의 과학사 자료를 도입해야 하고, 과학의 본성 요소를 적절히 반영하도록 교과서 도입에 있어 보다 다차원적인 접근이 이루어져야 할 것이다.

• 펄프종이기술
• /
• 제47권4호
• /
• pp.177-186
• /
• 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.

• 한국자동차공학회논문집
• /
• 제18권2호
• /
• pp.114-121
• /
• 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
• /
• 제9권4호
• /
• pp.482-489
• /
• 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.

• 대한지구과학교육학회지
• /
• 제16권1호
• /
• pp.30-42
• /
• 2023

이 연구는 초등 예비교사들이 작성한 과학 일기를 양적·질적 분석하여 초등 예비교사들이 지닌 과학의 본성에 대한 관점의 특징과 그 변화 과정을 분석하여 범주화하는데 그 목적이 있다. 이를 위해 초등 예비교사 13명이 쓴 과학 일기 112편을 분석하였다. 수집된 자료는 과학의 본성 4가지 영역의 연구 개념틀을 이용하여 영역별 빈도수를 분석하였고, VNOS-C 검사 분석틀을 이용하여 과학의 본성에 대한 관점 변화 양상을 귀납적으로 도출하여 유형화하였다. 그 결과 초등 예비교사들이 작성한 과학 일기에 나타난 과학의 본성에 대한 관점은 과학의 사고적 본성, 지식적 본성, STS적 본성, 탐구적 본성은 비교적 비슷한 비율로 서술되었으나 그 중 과학의 사고적 본성이 가장 높은 비율로 나타났고, 과학의 탐구적 본성이 가장 낮은 비율로 기술되었다. 과학 지식의 가변성, 경험적 증거의 중요성, 과학의 긍정적·부정적 작용에 대해서는 특히 집중적으로 언급되었다. 또한 초등 예비교사들의 과학의 본성에 대한 관점 변화 양상은 '고전적 관점 유지형', '현대적 관점 유지형', '회귀형', '발전형', '혼재형'으로 유형화 할 수 있었다. '과학 지식의 경험적 본성' 요소는 학생에 따라 변화 양상이 다양한 유형으로 나타났고, 대부분의 학생들이 과학 지식의 잠정성에 대해서는 현대적 관점을 여러 회기 동안 유지하였다.

• 한국환경복원기술학회지
• /
• 제8권1호
• /
• pp.52-62
• /
• 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.

• 한국환경복원기술학회지
• /
• 제27권2호
• /
• pp.29-42
• /
• 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.