• Tuberculosis and Respiratory Diseases
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• 제85권2호
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• pp.122-136
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• 2022

Although chronic obstructive pulmonary disease (COPD) and interstitial lung disease (ILD) have distinct clinical features, both diseases may coexist in a patient because they share similar risk factors such as smoking, male sex, and old age. Patients with both emphysema in upper lung fields and diffuse ILD are diagnosed with combined pulmonary fibrosis and emphysema (CPFE), which causes substantial clinical deterioration. Patients with CPFE have higher mortality compared with patients who have COPD alone, but results have been inconclusive compared with patients who have idiopathic pulmonary fibrosis (IPF). Poor prognostic factors for CPFE include exacerbation, lung cancer, and pulmonary hypertension. The presence of interstitial lung abnormalities, which may be an early or mild form of ILD, is notable among patients with COPD, and is associated with poor prognosis. Various theories have been proposed regarding the pathophysiology of CPFE. Biomarker analyses have implied that this pathophysiology may be more closely associated with IPF development, rather than COPD or emphysema. Patients with CPFE should be advised to quit smoking and undergo routine lung function tests, and pulmonary rehabilitation may be helpful. Various pharmacologic agents and surgical approaches may be beneficial in patients with CPFE, but further studies are needed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2744-2749
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• 2008

Numerical calculations are carried out for the natural convection induced by temperature difference between a cold outer square cylinder and a hot inner circular cylinder for Rayleigh number of $Ra=10^7$. This study investigates the effect of the inner cylinder location on the heat transfer and fluid flow. The location of inner circular cylinder ($\delta$) is changed vertically along the center-line of square enclosure. The natural convection bifurcates from unsteady to steady state according to $\delta$. Two critical positions of ${\delta}_{C,L}$ and ${\delta}_{C,U}$ as a lower bound and an upper bound are ${\delta}_{C,L}=0.05$ and ${\delta}_{C,U}=0.18$, respectively. Within the defined bounds, the thermal and flow fields are steady state. When the inner cylinder locates at ${\delta}{\geq}{\delta}_{C,U}$, the space between the upper surface of inner cylinder and the top surface of the enclosure forms a relatively shallow layer where the natural convection characterized as the pure Rayleigh-Benard convection forms alternately the upwelling and downwelling plums, as a result that a series of cells known as Benard cells is derived.

• Korean Chemical Engineering Research
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• 제52권2호
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• pp.199-204
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• 2014

2성분 응고계에서 다공성 mush 층에서의 조성 대류는 생성되는 제품의 질에 영향을 준다. 본 연구에서는 일정한 속도로 응고되는 mush 층을 고려하였다. 선형 안정성 이론을 사용하여 mush 층에 대한 교란방정식을 유도하였고, 기본상태 온도장과 mush 층에서 기공률의 분포를 수치해법으로 조사하였다. 과열량이 클 때 mush 층의 두께는 열경계층의 두께에 비해 상대적으로 작았다. 과열량이 감소함에 따라 mush 층의 두께를 기준으로 한 Rayleigh 수는 증가하였고, mush 층은 조성 대류에 대해 안정해졌다. mush 층의 윗면에 등온조건을 적용한 경우보다 온도 및 열속의 연속조건을 액체-mush 계면에 적용한 경우에 임계 Rayleigh 수가 더 작게 얻어졌다.

• 한국초전도ㆍ저온공학회논문지
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• 제16권3호
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• pp.7-9
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• 2014

Single-crystal like $MgB_2$ thin film was grown on (000l) $Al_2O_3$ substrate by using hybrid physical-chemical vapor deposition (HPCVD) system. Single crystal properties were studied by X-ray diffraction (XRD) and the full width at half maximum (FWHM) of the (0001) $MgB_2$ peak is $15^{\circ}$, which is very close to that has been reported for $MgB_2$ single-crystal. It indicates that the crystalline quality of thin film is good. Temperature dependence on resistivity was investigated by physical property measurement system (PPMS) in various applied fields from 0 to 9 T. The upper critical field ($H_{c2}$) and irreversibility field ($H_{irr}$) were determined from PPMS data, and the estimated values are comparable with that of $MgB_2$ single-crystals. The thin film shows a high critical temperature ($T_c$) of 40.4 K with a sharp superconducting transition width of 0.2 K, and a high residual resistivity ratio (RRR=21), it reflects that $MgB_2$ thin film has a pure phase structure.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
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• pp.248-251
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• 2000

The fabrication and characteristics of HTS race-track type field coil for generators was carried out. Field coils are composed of 3 pancake coils wound by 37-filamental Bi-2223/Ag-alloy tapes. The winding machine is horizontal type. The critical currents (I$_c$) of the superconducting tapes were measured with variation of bending strain and external magnetic fields. I$_c$ of both whole field coils and 3 pancake coils were measured as a function of temperature. At 77K under the self-field, I$_c$ of whole field coils was 12A, while in the case of middle pancake coil, I$_c$ was 15A. The distribution of magnetic field B was obtained, using 3-D FEM. Our simulation showed that maximums of B${\bot}$A in x-y plane were locally distributed in both the upper and the lower coils. In addition, the fabrication processes and the characteristics of field coil are described.

• 대한기계학회논문집
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• 제14권1호
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• pp.1-12
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• 1990

본 연구에서는 자유단조용 프레서를 이용하여 돌출부가 있는 비대칭 중공형단 조 제품을 생산할 수 있도록 금형장치를 설계.제작하고, Fig.1에서 보는 바와 같이 경 사진 돌출부가 있는 비축대칭 복합단조에 UBET를 적용하여 해석하였다. 단조시편은 원주형태를 가지도록 하였다. 즉 원주형 소재가 요구되는 비축대칭 단조제품으로 변 형되는 과정에서 단조하중, 재료가 돌출부를 충만하도록 하는 유동특성, 재료가 돌출 부로 차들어가는 속도 등에 영향을 주는 인자(예:펀치 직경의 크기, 금형 상하면의 각 도)의 특성을 이론적으로 해석하고 실험으로 확인하였다.

• 농촌계획
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• 제7권1호
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• pp.37-48
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• 2001

The purpose of this study is to suggest the landscape potential index for visualizing landscape information in the conservation of hilly landscape in urban fringe. For the visual and quantitative approach to topological landscape assessment, numerical entity data of DEM(digital elevation model) were processed with CAD-based utilities that we developed and were mainly focused on analysis of visibility and visual sensitivity. Some results, with reference in assessing greenbelt area of Eodeung Mt. in Gwangju, proved to be considerable in the landscape assessment of suburban hilly landscapes. 1) Since the viewpoints and viewpoint fields were critical to landscape structure, randomized 194 points(spatially 500m interval) were applied to assessing the generalized visual sensitivity, we called. Because there were similar patterns of distribution comparing to those by 56 points and 18 Points given appropriately, it could be more efficient by a few viewpoints which located widely. 2) Regressional function was derived to represent the relationships between probabilities of visibility frequency and the topological factors(topological dominance, landform complexity and relational aspect) of target field. 3) Visibility scores of each viewpoint were be calculated by summing the visual sensitivity indices within a scene. The scores to the upper part including ridge line have been more representative to overall distributions of visual sensitivities. Also, with sum of deviations of sensitivity indices from each single point's specific index to the weighting values of view points could be estimated rotationally. 4) The deviational distributions of visual sensitivity classes in the topological unit of target field were proved to represent the visual vulnerability of the landform. 5) Landscape potential indices combined with the visual sensitivity and the DGN(degree of green naturality) were proposed as visualized landscape information distributed by topological unit.

• 대한기계학회논문집B
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• 제34권8호
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• pp.739-747
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• 2010

고온의 내부 원형 실린더가 존재하는 저온의 사각 밀폐계 사이의 온도차이에 의해 발생하는 자연대류에 관해 수치해석을 수행하였다. 본 연구는 내부의 원형 실린더를 표현하기 위해 유한 체적법에 기초한 가상 경계법을 사용하여 Ra = $10^7$ 에서 2 차원 비정상상태의 자연대류 현상에 대한 해를 얻었다. 더욱이 밀폐계의 수직 중심선에 따른 내부 원형 실린더의 위치 변화에 의한 열전달과 유동에 관한 영향을 연구하였다. 내부원형 실린더의 위치 변화에 따라 자연대류 현상은 비정상상태에서 정상상태로 변화 되었다. 연구 결과 두가지의 임계 위치를 얻을 수 있었다. 하부 경계는 0.05 인 지점이고 상부경계는 0.18 인 지점이다. 하부 경계와 상부 경계의 사이의 위치에서는 열 및 유동장이 정상상태임을 알 수 있었다.

• 태양에너지
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• 제19권3호
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• pp.29-41
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• 1999

본 연구에서는 돌출된 단일 모듈이 부착된 수직 채널내의 3차원 자연대류 특성을 실험적으로 조사하였으며, 특히 모듈로부터 대류에 의한 열에너지 제거에 초점을 두었다. 채널내의 유동장은 smoke-method를 이용하여 가시화 하였다. 또한 채널내부, 수직벽면 및 모듈표면의 국소온도를 열전대와 열플럭스 센서를 이용하여 측정하여 복사와 전도에의한 열손실량을 계산하였다. 실험결과 대류열전달은 모듈 하부의 모서리 부근에서 가장 활발히 일어나고, 모듈 상부에서의 재순환영역은 열전달을 감소시킴을 알 수 있으며 임계 채널간격비를 예측할 수 있는 상관식을 레일리히수의 함수로 구하였다. 또한 $8.28{\times}10^3<Ra^*_c<3.48{\times}10^6$의 범위에서 수정 채널 레일리히수의 함수로써 평균 누셀트수와의 상관식을 구하였다.

• Steel and Composite Structures
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• 제46권4호
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• pp.471-483
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• 2023

This paper presents an analytical hyperbolic theory based on the refined shear deformation theory for mechanical stability analysis of the simply supported advanced composites plates (exponentially, sigmoidal and power-law graded) under triangular, trapezoidal and uniform uniaxial and biaxial loading. The developed model ensures the boundary condition of the zero transverse stresses at the top and bottom surfaces without using the correction factor as first order shear deformation theory. The mathematical formulation of displacement contains only four unknowns in which the transverse deflection is divided to shear and bending components. The current study includes the effect of the geometric imperfection of the material. The modeling of the micro-void presence in the structure is based on the both true and apparent density formulas in which the porosity will be dense in the mid-plane and zero in the upper and lower surfaces (free surface) according to a logarithmic function. The analytical solutions of the uniaxial and biaxial critical buckling load are determined by solving the differential equilibrium equations of the system with the help of the Navier's method. The correctness and the effectiveness of the proposed HyRPT is confirmed by comparing the results with those found in the open literature which shows the high performance of this model to predict the stability characteristics of the FG structures employed in various fields. Several parametric analyses are performed to extract the most influenced parameters on the mechanical stability of this type of advanced composites plates.