• 제목/요약/키워드: Concentric work

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스펙트럴 클러스터링 - 요약 및 최근 연구동향 (Spectral clustering: summary and recent research issues)

  • 정상훈;배수현;김충락
    • 응용통계연구
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    • 제33권2호
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    • pp.115-122
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    • 2020
  • K-평균 클러스터링은 매우 널리 사용되고 있으나 유사도가 구면체 또는 타원체로 정의되어 각 클러스터가 볼록 집합 형태인 자료에는 좋은 결과를 주지만 그렇지 않은 경우에는 매우 형편 없는 결과를 나타낸다. 스펙트럴 클러스터링은 K-평균 클러스터링의 단점을 잘 보완해 줄 뿐아니라 여러 형태의 자료나 고차원 자료 등에 대해서도 좋은 결과를 나타내서 최근 인공 신경망 모형에 많이 이용되고 있다. 하지만, 개선되어야 할 단점도 여전히 많다. 본 논문에서는 스펙트럴 클러스터링에 대해 알기 쉽게 소개하고, 클러스터 갯수의 추정, 척도모수의 추정, 고차원 자료의 차원 축소 등 스펙트럴 클러스터링에 대한 최근의 연구 동향을 소개한다.

Quality Enhancement of a Complex Holographic Display Using a Single Spatial Light Modulator and a Circular Grating

  • Bang, Le Thanh;Piao, Yan Ling;Kim, Jong Jae;Kim, Nam
    • Journal of the Optical Society of Korea
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    • 제20권1호
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    • pp.70-77
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    • 2016
  • This paper proposes an optical system for complex holographic display that enhances the quality of the reconstructed three-dimensional image. This work focuses on a new design for an optical system and the evaluation of the complex holographic display, using a single spatial light modulator (SLM) and a circular grating. The optical system is based on a 4-f system in which the imaginary and real information of the hologram is displayed on concentric rectangular areas of the SLM and circular grating. Thus, this method overcomes the lack of accuracy in the pixel positions between two window holograms in previous studies, and achieves a higher intensity of the real object points of the reconstructed hologram than the original phase-reconstructed hologram. The proposed method provides approximately 30% less NMRS (Normal Root Mean Square) error, compared to previous systems, which is verified by both simulation and optical experiment.

냉매 충전량에 따른 CO2용 수냉식 열펌프의 성능 특성에 관한 연구 (Performance Characteristics of Water-Chilling Heat Pump Using CO2 on Variation of Refrigerant Charge Amount)

  • 손창효;유태근;장승일;오후규
    • Journal of Advanced Marine Engineering and Technology
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    • 제31권5호
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    • pp.558-566
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    • 2007
  • The performance characteristics of water-chilling heat pump using $CO_2$ with respect to variation of refrigerant charge amount was investigated experimentally. An experimental apparatus is consisted of a compressor, a gas cooler, an expansion valve, an evaporator and a liquid receiver. All heat exchangers used in the test rig are counter-flow-type heat exchangers with concentric dual tubes, which are made of copper. The gas cooler and the evaporator consist of 6 and 4 straight sections respectively arranged in parallel, each has 2400 mm length. The experimental results summarize as the followings : As the refrigerant charge ratio of $CO_2$ heat pump system increases, the discharge pressure and compressor ratio increases, but mass flow rate of refrigerant decreases. Also the compressor work increases with the increase of refrigerant charge ratio. However, the heating and cooling capacity of $CO_2$ heat pump decreases as the refrigerant charge ratio increases. The maximum heating COP of $CO_2$ heat pump system presented at 0.25 refrigerant charge ratio. It is possible to confirm the optimum charge ratio of $CO_2$ heat pump system by the viewpoint of heating COP.

Thermal Performance of a Spirally Coiled Finned Tube Heat Exchanger Under Wet-Surface Conditions

  • Wongwises Somchai;Naphon Paisarn
    • Journal of Mechanical Science and Technology
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    • 제20권2호
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    • pp.212-226
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    • 2006
  • This paper is a continuation of the authors' previous work on spiral coil heat exchangers. In the present study, the heat transfer characteristics and the performance of a spirally coiled finned tube heat exchanger under wet-surface conditions are theoretically and experimentally investigated. The test section is a spiral-coil heat exchanger which consists of a steel shell and a spirally coiled tube unit. The spiral-coil unit consists of six layers of concentric spirally coiled finned tubes. Each tube is fabricated by bending a 9.6 mm diameter straight copper tube into a spiral-coil of four turns. The innermost and outermost diameters of each spiral-coil are 145.0 and 350.4 mm, respectively. Aluminium crimped spiral fins with thickness of 0.6 mm and outer diameter of 28.4 mm are placed around the tube. The edge of fin at the inner diameter is corrugated. Air and water are used as working fluids in shell side and tube side, respectively. The experiments are done under dehumidifying conditions. A mathematical model based on the conservation of mass and energy is developed to simulate the flow and heat transfer characteristics of working fluids flowing through the heat exchanger. The results obtained from the present model show reasonable agreement with the experimental data.

Structural behavior of concrete walls reinforced with ferrocement laminates

  • Shaheen, Yousry B.I.;Refat, Hala M.;Mahmoud, Ashraf M.
    • Structural Engineering and Mechanics
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    • 제78권4호
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    • pp.455-471
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    • 2021
  • The present work focuses on experimental and numerical performance of the ferrocement RC walls reinforced with welded steel mesh, expanded steel mesh, fiber glass mesh and tensar mesh individually. The experimental program comprised twelve RC walls having the dimensions of 450 mm×100 mm×1000 mm under concentric compression loadings. The studied variables are the type of reinforcing materials, the number of mesh layers and volume fraction of reinforcement. The main aim is to assess the influence of engaging the new inventive materials in reinforcing the composite RC walls. Non-linear finite element analysis; (NLFEA) was carried out to simulate the behavior of the composite walls employing ANSYS-10.0 Software. Parametric study is also demonstrated to check out the variables that can mainly influence the mechanical behavior of the model such as the change of wall dimensions. The obtained numerical results indicated the acceptable accuracy of FE simulations in the estimation of experimental values. In addition, the strength gained of specimens reinforced with welded steel mesh was higher by amount 40% compared with those reinforced with expanded steel mesh. Ferrocement specimens tested under axial compression loadings exhibit superior ultimate loads and energy absorbing capacity compared to the conventional reinforced concrete one.

Analytical crack growth in unidirectional composite flywheel

  • Lluis Ripoll;Jose L. Perez-Aparicio;Pere Maimi;Emilio V. Gonzalez
    • Coupled systems mechanics
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    • 제12권2호
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    • pp.183-197
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    • 2023
  • Scarce research has been published on crack propagation fracture of flywheels manufactured with carbon fiber-reinforced polymers. The present work deals with a calculation method to determine the conditions for which a crack propagates in the axial direction of the flywheel. The assumptions are: flywheels made with just a single thick ply or ply clustering laminates, oriented following the hoop direction; a single crack is analyzed in the plane defined by the hoop and axial directions; the crack starts close to one of the free edges; its axial length is initially large enough so that its tip is far away from that free edge, and the crack expands the entire circumferential perimeter and keeps its concentric position. The developed method provides information for a good design of flywheels. It is concluded that a fracture-based crack propagation criterion generally occurs at a lower speed than a stress-based criterion. Also, that the evolution of failure with thickness using the fracture criterion is exponential, demonstrating that thin flywheels are relatively not sensitive to crack propagation, whereas thick ones are very prone.

The effects of drag reducing polymers on flow stability : Insights from the Taylor-Couette problem

  • Dutcher, Cari S.;Muller, Susan J.
    • Korea-Australia Rheology Journal
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    • 제21권4호
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    • pp.213-223
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    • 2009
  • Taylor-Couette flow (i.e., flow between concentric, rotating cylinders) has long served as a paradigm for studies of hydrodynamic stability. For Newtonian fluids, the rich cascade of transitions from laminar, Couette flow to turbulent flow occurs through a set of well-characterized flow states (Taylor Vortex Flow, wavy Taylor vortices, modulated wavy vortices, etc.) that depend on the Reynolds numbers of both the inner and outer cylinders ($Re_i$ and $Re_o$). While extensive work has been done on (a) the effects of weak viscoelasticity on the first few transitions for $Re_o=0$ and (b) the effects of strong viscoelasticity in the limit of vanishing inertia ($Re_i$ and $Re_o$ both vanishing), the viscoelastic Taylor-Couette problem presents an enormous parameter space, much of which remains completely unexplored. Here we describe our recent experimental efforts to examine the effects of drag reducing polymers on the complete range of flow states observed in the Taylor-Couette problem. Of particular importance in the present work is 1) the rheological characterization of the test solutions via both shear and extensional (CaBER) rheometry, 2) the wide range of parameters examined, including $Re_i$, $Re_o$ and Elasticity number E1, and 3) the use of a consistent, conservative protocol for accessing flow states. We hope that by examining the stability changes for each flow state, we may gain insights into the importance of particular coherent structures in drag reduction, identify simple ways of screening new drag reducing additives, and improve our understanding of the mechanism of drag reduction.

여성건강을 위한 개념적 모형 (Conceptual Model for Women s Health)

  • 이경혜
    • 대한간호학회지
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    • 제27권4호
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    • pp.933-942
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    • 1997
  • There has recently been an increased interest in women's health from, various disciplines, with different perspectives presented according to each profession's academic background. This has led to many instances of incorrectly defining, or misinterpretation, of the issues even among professionals. Nurse scholars as well as practitioners who work in women's health care need to have a clear conceptual understanding of women's health in order to build a body of knowledge, delineate curricular activities, and set directions for professional nursing interventions. In addition, a conceptual model that may be directly utilized in practice is needed to maintain and promote women's health issues. The purpose of this study was to apply a Hybrid model, analyzing conceptual definitions and discussions related to women's health gathered from review of the literature. Further to compare analyticals the concepts and properties observed from field work, so as to present a final definition of women's health and, build a conceptual framework for a united comprehensive perspective on the concept as well as on nursing practice. Data collection and analysis consisted of a theoretical stage, field work stage, and final analysis. A heterogeneous group of professionals and lay persons, 39 in all, participated in the field work. Study findings Include several subconcepts under the concept of women's health : a woman's whole life, holistic health, quality of life, awareness of being a woman, individual nursing, self care ability, reproductive health, and family health. Thus, a comprehensive definition was built, 1. e., "Women's health care be defined as improvement in the quality of life of women through attainment of holistic health throughout the life span. With reproductive health at the core, the concept is directly related to family and national health, and includes taking care of one's own health based on awareness of being a woman and utilizing self care activities. Women's health care issues are unique and allow various responses, therefore women's health professionals need to apply individual approaches to reach solutions in attaining holistic health and improving quality of life." The constructual factors of women's health were found to be reproductive functions, diseases more common in woman, self actualization, mental health, women's health policies, sexuality, midlife changes, and marital relations, with each factor having more than three properties. Positive factors affecting women's health were found to be a normal childbearing process, a healthy lifestyle, active health management, health information, support, and resources, and interpersonal relationships. Negative factors were found to be overwhelming role stress, cultural oppression, gender inequality, distorted sexual identity, economic difficulties, misuse and/or abuse of substances, and stress. The model of women's health may be visualized as a balance scale set upon a woman's life, supporting 4 concentric circles. The innermost circle and second circle incorporate conceptual definitions of women's health, and the outer two circles represent the constructional factors and properties of women's health. Each circle has its own color that symbolizes the conceptual meaning. Positive and negative factors are represented as weights at either end of the scale, and are affected by nursing intervention, i. e., health and wellness increase when positive factors are stronger, whereas disease and illness increase when negative factors are stronger. This model is only a preliminary effort and requires much discussion and testing to be further developed. Continuous research is also required.

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수평식 이중원통형 ZrCo 용기 내 수소 흡탈장 및 열전달 모델링 (Hydrogen Absorption/Desorption and Heat Transfer Modeling in a Concentric Horizontal ZrCo Bed)

  • 박종철;이정민;구대서;윤세훈;백승우;정흥석
    • 한국수소및신에너지학회논문집
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    • 제24권4호
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    • pp.295-301
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    • 2013
  • Long-term global energy-demand growth is expected to increase driven by strong energy-demand growth from developing countries. Fusion power offers the prospect of an almost inexhaustible source of energy for future generations, even though it also presents so far insurmountable scientific and engineering challenges. One of the challenges is safe handling of hydrogen isotopes. Metal hydrides such as depleted uranium hydride or ZrCo hydride are used as a storage medium for hydrogen isotopes reversibly. The metal hydrides bind with hydrogen very strongly. In this paper, we carried out a modeling and simulation work for absorption/desorption of hydrogen by ZrCo in a horizontal annulus cylinder bed. A comprehensive mathematical description of a metal hydride hydrogen storage vessel was developed. This model was calibrated against experimental data obtained from our experimental system containing ZrCo metal hydride. The model was capable of predicting the performance of the bed for not only both the storage and delivery processes but also heat transfer operations. This model should thus be very useful for the design and development of the next generation of metal hydride hydrogen isotope storage systems.

A COMPREHENSIVE VIEW OF LARGE-SCALE MAGNETIC FIELDS, WITH EMPHASIS ON THE GALACTIC MAGNETIC FIELD NEAR THE SUN

  • HEILES CARL
    • 천문학회지
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    • 제29권spc1호
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    • pp.151-154
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    • 1996
  • We examine the observations of large-scale magnetic fields in the Universe. We begin at the largest scale with clusters of galaxies and work our way down through galaxies and finally to the Milky Way. on which we concentrate in detail. We examine the observations of the Galactic magnetic field, and their interpretation, under the philosophy that the Galactic magnetic field is like that in other spiral galaxies. We use pulsar data. diffuse Galactic synchrotron emission, and starlight polarization data to discuss the Galaxy's global magnetic configuration and the uniform ($B_u$), random ($B_r$), and total ($B_t$) components of the field strength. We find disagreement among conclusions derived from the various data sets and argue that the pulsar data are not the best indicator for large-scale Galactic field. Near the Solar circle, we find that the azimuthal average of $B_t$ is 4.2$\mu$G and we adopt $B_u\~$2.2 and $B_r\~3.6{\mu}G$. $B_t$ is higher in spiral arms, reaching $\~5.9{\mu}G$. $B_t$ is higher for smaller $R_{Gal}$, reaching $\~8.0{\mu}G$ for $R_{Gal}$ = 4.0 kpc. The pattern of field lines is not concentric circles but spirals. The inclination of the magnetic spiral may be smaller than that of the Galaxy's spiral arms if our sample, which refers primarily to the interarm region near the Sun, is representative. However, it is not inconceivable that the local field lines follow the Galaxy's spiral pattern, as is observed in external galaxies.

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