• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.297-303
• /
• 2000

Natural convection heat transfer have been paid attention because it can be applied to various areas such as cooling of nuclear reactor, heat storing system and so on. Among such applications, the melting process of phase change material(PCM) has been actively studied. However most researches have focused on phase change heat transfer in natural melting. Therefore, In this paper, ultrasonic vibration was adopted to increase the melting rate. In addition, general relationship and corelationship between melting with ultrasonic vibration and melting without ultrasonic vibration have been established during the melting of PCM.

• 농촌계획
• /
• 제25권3호
• /
• pp.129-139
• /
• 2019

The purpose of this study is to monitor the long-term vegetation change of the village complementary forest after restoration. Based on the monitoring in 2010, six years after the restoration project in 2004, the monitoring of the complementary forest in Dubang village in 2019 after 9 years was conducted. This study identifies the change of species diversity and structure, growth, vegetation coverage, structural quality etc. and succession through long-term monitoring. For this, field survey was conducted in 2003 and 2010, 2019. The results demonstrate significant increase of species diversity and multi-layer structure and progress of natural succession. Overall, Part I is considered to be a quasi-natural complementary village forest, which has a natural balance between natural vegetation that have remained in nature for a long time and anthropogenic vegetation, revealing the coexistence of nature and humanity. It means ecological structure and function have improved. Part II should be restored to the lost part and adaptive management rather than excessive management should be carried out to leave natural succession.

• 한국산림과학회지
• /
• 제94권4호통권161호
• /
• pp.252-257
• /
• 2005

최근 재해에 대한 관심이 높아지고 있음에도 불구하고 재해에 대한 장기적인 변화분석은 미흡한 실정이다. 따라서 자연재해의 주범인 기상재해 및 산지토사재해에 의한 희생자 수의 장기적인 변화를 분석하였고, 자연재해에 대한 산지토사재해의 비율 및 산지토사재해 발생면적변화를 조사하였다. 그 결과 최근 강우강도의 증가에도 불구하고 자연재해 및 토사재해에 의한 희생자 수는 점차 감소하고 있는 것으로 나타났다. 자연재해는 1970년대 연간 250명에서 1990년대 연간 140명 수준으로 감소하였고, 토사재해는 1970년대 60명/년에서 1990년대 20명/년으로 감소하였다. 특히 토사재해의 경우 자연재해에 대한 감소비율이 1970년대 2/7에서 1980년대 이후 2/15로 줄어들었다. 그러나 산사태 발생면적(1981년: 206ha $\rightarrow$ 1999년: 688ha)이 계속 증가하고 있으므로 유역관리개념을 도입한 새로운 사방사업의 추진과 종합적인 산지토사재해 관리 시스템 구축이 요구되는 것으로 판단되었다.

• 한국가스학회지
• /
• 제20권6호
• /
• pp.58-64
• /
• 2016

본 연구에서는 굴곡진 배관에서 내부 유체의 유동속도의 변화에 따른 진동특성을 고찰 하였다. 해밀톤의 원리에 근거하여 운동방정식을 유도하고 굽어진 배관계의 유한요소 방정식을 구성한 후, 진동수 방정식을 풀이하여 고유 진동수를 구하였다. 곡관부에 가해지는 초기 인장력을 무시하였을 경우에는 내부 유체의 유동속도가 증가함에 따라 파이프의 고유진동수의 값은 감소하였다. 초기 인장력을 고려할 경우에는 내부 유동속도의 변화에 상관없이 파이프의 고유진동수가 변하지 않았다. 배관의 자유진동 평가 시, 정확한 고유진동수를 구하기 위해서는 시스템 운동방정식을 구성할 때, 초기인장력을 반드시 고려하여야한다. 공진을 회피하기 위해서는 파이프의 강성 및 지지점의 위치를 변화시킴으로써 시스템의 기계적 성질을 조절해야 한다. 고유진동수는 가진 진동수 범위로부터 이격시켜야 한다. 엘보우의 각도는 제1차 고유진동수에 영향을 미치지 않음이 고찰되었으나, 3차 모드나 그 이상의 고주파 모드에서는 영향을 미쳤다.

• 한국방재학회:학술대회논문집
• /
• 한국방재학회 2007년도 정기총회 및 학술발표대회
• /
• pp.323-326
• /
• 2007

Recently, occurrence frequency of natural disasters decrease but scale of damage increase remarkably by the Climate change due to global warming. Especially, extreme heat become more critical weather problem in the Korean Peninsula. But, we don't have exact threshold about extreme heat. Extreme heat does not classify into natural disaster. Therefore, we have compared death count of the natural disaster with the one of extreme heat at Seoul, Korea. As a result, the number of death by extreme heat don't smaller than one by the natural disasters and we knew extreme heat have also to consider as natural disaster.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 춘계학술대회논문집B
• /
• pp.51-56
• /
• 2000

The Finite Element Solutions Is reported on solid-liquid phase change in porous media with natural convection including freezing. The model is based on volume averaged transport equations, while phase change is assumed to occur over a small temperature range. The FEM (Finite Element Method) algorithm used in this study is 3-step time-splitting method which requires much less execution time and computer storage the velocity-pressure integrated method and the penalty method. And the explicit Lax-Wendroff scheme is applied to nonlinear convective term in the energy equation. For natural convection including melting and solidification the numerical results show reasonable agreement with FDM (Finite Difference Method) results.

• Journal of Community Nutrition
• /
• 제7권1호
• /
• pp.8-20
• /
• 2005

The study purpose was to examine which factors including health perceptions & behaviors, psychosocial factors, dietary intakes were different by stages of change to reduce fast food consumption among university students. Survey data(n = 341) were analyzed using X$^2$ test or analysis of variance. With respect to stages of change, $17\%$ were in the precontemplation ; $21.4\%$ for contemplation, $19.7\%$ for preparation, 11.7% for action, and $30.2\%$ for the maintenance stage. Frequency of fast food consumption (p < 0.001), health status, interest toward health, and exercising behavior (p < 0.05) differed significantly by stages of change. Demographics and nutrient intakes, however, had no association with stages of change. Those in precontemplation through preparation stages felt more strongly on the advantages such as taste, satiety, cleanness of restaurants (p < 0.001), and diverse menus (p < 0.05). Compared to maintainers or actors, pre-contemplators agreed less to the disadvantages of eating fast foods, including sanitary problems (p < 0.001), overeating, indigestion, decreased vegetable intakes (p < 0.01) and loss of freshness (p < 0.05). Influence of significant others (e.g., friends, siblings, parents) significantly differed by stages of change. Compared with maintainers, those in preaction stages felt less control over facilitators or situations for fast food consumption. These included 'others like fast foods', 'providing standard meals', 'when I don't have foods for meals'(p < 0.001), availability, advertisement, 'socially popular', 'when I feel hungry'(p < 0.01), and 'when I don't like to prepare meals' (p < 0.05). These results suggested that nutrition education be planned considering one's stages of change for fast food consumption. For those in preaction stages, it is desirable to use motivational strategies to increase benefits and remove barriers of change, and help to develop skills to deal with situations or factors for fast food consumption. The support from friends or families is also needed to move to further stages.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
• /
• pp.978-980
• /
• 2003

This study explores the temporal and spatial features near 67years (1934 ?2001) and landcover change in last 14 years (1987-2001) in Shijiazhuang, China, based on 67-year time series data edited from historical maps, TM and ETM+ imageries by integrating GIS and remote sensing method. An index named Annual Growth Rate (AGR) is used to analyze the spatial features of urban sprawl, and Maximum Likelihood classification method is utilized to detect the land cover types change. At last, the relationship between urbanization and factors is analyzed.

• Journal of the Korean Wood Science and Technology
• /
• 제50권1호
• /
• pp.31-45
• /
• 2022

After manufacturing the natural dyed actual size Hanji using 11 kinds of plant natural dyeing materials and 2 kinds of animal natural dyeing materials, the color characteristics and color change and color fastness after post-mordanting were compared and discussed. The hues of 13 types of natural dyed Hanji were black, PB, and RP, each with 1 type, YP with 3 types, and Y with 7 types. Among the natural dyeing materials, Chinese ink, indigo and Lac showed high color yield and color difference, and violet-root cromwell and gardenia seeds showed low color yield. The color fastness of Hanji dyed with turpentine diluted Ottchil, Pagoda tree seeds, Chinese ink and indigo was excellent, while that of gardenia seeds and violet-root cromwell were very poor. After post-mordanting of natural dyed Hanji with Al, Cu, and Fe mordants, the hue changes were show up the Alnus firma, clove, lac and cochineal. In addition, the color difference was very diverse and was overall the most biggest due to Fe mordant. After 72 hr. of UV irradiation on post-mordanting natural dyed Hanji, hue change was observed in 3 types and color fastness was improved in 8 types by post-mordanting. The Hue and color fastness are significantly different depending on the type of natural dying materials and post-mordants. Therefore, when dyeing Hanji with natural dyes, it is necessary to dye with sufficient knowledges and informations about the desired color and fastness.

• Elastomers and Composites
• /
• 제19권3호
• /
• pp.163-177
• /
• 1984

The effect of curing temperature increase and sulfur amount added were studied with natural and synthetic rubbers. Also, the effects of TMTD, MBTS and mixture of zinc soaps of high molecular fatty acids added to natural rubber were investigated respectively. The experimental results showed that, in the case of the conventional curing ($145^{\circ}C$), natural rubber, compared with synthetic rubber, gave higher values in elongation, tensile strength, cure rate, and lower values in modulus change. But, at high temperature curing ($180^{\circ}C$), natural rubber showed faster reversion rate, and higher heat build-up compared to synthetic rubber, than in the conventional curing. Also, natural rubber produced at high temperature showed severe degradation in hardness and tensile strength before heat-aging as well as in hardness, modulus and tensile strength after heat-aging. Improved reversion effect was obtained with natural rubber either by blending mixture of zinc soaps of high molecular acids or by applying semi-efficient vulcanization system.