• 한국세라믹학회지
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• 제35권12호
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• pp.1274-1279
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• 1998

The glass forming ability of the PbO-B2O3-TiO3-BaO system was investigated in relation to transitieon tem-peratures and the atomic ratio between constituents. Glass forming tendency was improved as the tem-peratures and the atomic ratio between constituents. Glass forming tendency was improved as the tem-perature differences between liquidus temperature and crystallization(or glass transition) temperature de-creased and the temperature difference between crystallization and glass transition temperature increases. The atomic ratio could be used as a criterion to deign glass systems. The interposition of B and Ba atoms between Pb and Ti atoms was one of important factors in glass formation.

• 한국주조공학회지
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• 제20권3호
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• pp.197-207
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• 2000

Al-Si alloys were solidified in a rotating cylindrical mold by a vertical centrifugal casting process. Under a certain casting condition, there are four distinct zones such as the chill zone, the primary fine columnar zone, the equiaxed zone, and the secondary coarse columnar zone from the mold wall. The columnar-equiaxed transition (CET) and the equiaxed-columnar transition (ECT) were measured as functions of solute content, flow rate (mold velocity), pouring temperature and mold temperature. Within the critical value of solute content, as the flow rate increases, the columnar-equiaxed transition were found, but not the equiaxed-columnar transition. The aspect ratio of the primary columnar zone was more affected by the solute content than the flow rate. However the aspect ratio of the equiaxed zone was more affected by the flow rate than the solute content. The aspect ratio of the secondary columnar zone was affected by both the flow rate and the solute content.

• 한국수소및신에너지학회논문집
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• 제24권6호
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• pp.472-479
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• 2013

A free piston linear engine could be operated under HCCI combustion due to its variable compression ratios. To obtain HCCI combustion, the free piston linear engine needs a high compression ratio to achieve auto-ignition of the fuel/air mixture. In this study, an idea for obtaining a high compression ratio using the transition from SI combustion to HCCI combustion was proposed. The fuel used in this study is hydrogen, which is considered to be an environmentally friendly fuel. Besides, the effects of key parameters such as equivalence ratio (${\phi}$), load resistance ($R_L$) and intake temperature ($T_{in}$) on the SI-HCCI transition were numerically investigated. The simulation results show that the SI-HCCI transition is successful without any significant reduction of in-cylinder pressure as the intake temperature is increased from $T_{in}$=300K (SI mode) to $T_{in}$=450K (HCCI mode), while the load resistance and equivalence ratio are retained respectively at $R_L=120{\Omega}$ and ${\phi}$=0.6 in both SI mode and HCCI mode.

• 오토저널
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• 제15권3호
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• pp.81-88
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• 1993

This report describes the experimental research on the flow phenomena of the aq uaous polymer solution within the Cuette flow of the concentric, cylinders type with a wide circular gap. We have investigated the phenomena of the fluid flow through torque measuring in the system that the inner cylinder is stationary and the outer one is rotating. Geometrical parameters of the system are the gap ratio of t/R$_{0}$=0.2 and Aspect ratio of l/t=100. The torque increases considerably in about 420-480RPM, So, it is considered a turbulent transition boundary, the higher plymer concentration is, the lower torque value is and the higher transition Reynolds number is. In each of the polymer concentration, the unstable boundary of torque, that is, idiosyncrasies of torque is observed around 220-280RPM. and the boundary is looked upon as a resonant vibration which is caused by the inner cylinder and tortional vibration of torque sensor.r.

• 대한기계학회논문집A
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• 제25권5호
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• pp.816-822
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• 2001

The thermoforming process is widely used in the plastics industry to produce articles for the packaging, automotive, domestic construction and leisure industries. The microcellular foaming process appeared at M.I.T. in 1980s to save a quantity of polymer materials and increase their mechanical properties. The glass transition temperature of polymer materials is one of many important process variables in appling the microcellular foaming process to the conventional thermoforming process. The goal of this research is to evaluate the relation between gas absorption and glass transition temperature in batch process using microcellular foaming process. The weight gain ratio of polymer materials has a conception of gas absorption. Polymers such as acrylonitrile-butadiene-styrene(ABS), polystyrene(PS) have been used in this experiment. According to conventional Chows model and Cha-Yoon model, it was estimated with real experimental result to predict a change of glass transition temperature as a function of the weight gain ratio of polymer materials in batch process to gain microcellular foamed plastic products.

• 한국건설순환자원학회논문집
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• 제8권4호
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• pp.537-544
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• 2020

Interfacial transition zone (ITZ)은 골재-시멘트 복합체 사이의 영역으로써, 콘크리트에서 가장 취약한 영역으로 알려져 있으며, 이는 점진적으로 변화하는 불균질한 상으로 이루어져 있다. 경량 고강도 콘크리트 개발을 위해 물-바인더 비가 낮은 고강도 시멘트 복합체와 경량골재 사이의 Interfacial transition zone (ITZ)의 역학적 특성 평가는 필수적이다. 하지만 ITZ는 복잡하고 다공성 구조를 가지고 있기 때문에, 이의 역학적 특성은 아직 명확하지 않다. 또한, 경량골재 ITZ는 일반골재보다 다양한 변수 (물-바인더 비, 골재의 흡수율, 양생조건 등)에 의해 변화한다. 따라서 본 연구에서 골재의 종류 및 크기에 따른 ITZ의 역학적 특성을 분석하고자 한다. 이를 위해 나노 인덴테이션 기법을 이용하여 물-바인더 비가 0.2인 고강도 시멘트 복합체와 표준사 및 최대치수가 각각 2mm, 5mm인 경량골재 ITZ의 탄성계수를 측정하였다.

• 한국연소학회지
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• 제13권4호
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• pp.16-25
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• 2008

Experiments have been conducted to clarify impacts of curtain flow and velocity ratio on low strain rate flame extinction, and to further display transition of shrinking flame disk to flame-hole. Critical mole fractions at flame extinction are examined in terms of velocity ratio, global strain rate, and nitrogen curtain flow rate. It is shown that multi-dimensional effects at low strain rate flames through global strain rate, velocity ratio, and curtain flowrate dominantly contribute to flame extinction and transition of shrinking flame disk to flame hole. Our concerns are particularly focused on the dynamic behavior of an edge flame in shrinking flame disk.

• Journal of the Korean Statistical Society
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• 제35권4호
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• pp.355-376
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• 2006

To identify whether the sequence of observations follows a chain dependent process and whether the chain dependent or repeated observations follow stationary process or not, alternative procedures are suggested in this paper. These test procedures are formulated on the basis of logistic regression model under the likelihood ratio test criterion and applied to the daily rainfall occurrence data of Bangladesh for selected stations. These test procedures indicate that the daily rainfall occurrences follow a chain dependent process, and the different types of transition probabilities and overall transition probabilities of Markov chain for the occurrences of rainfall follow a stationary process in the Mymensingh and Rajshahi areas, and non-stationary process in the Chittagong, Faridpur and Satkhira areas.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.351-357
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• 2007

The transition zone between railway embankment and structures, or different track types is known to be an area in which problems often arise and where extra care needs to be taken with maintenance. Differences in track stiffness have dynamic effects and these increase the force in the track and the extent of deformation. In this study, the criteria for the change ratio of track stiffness along transition area, and proper transition length are presented through train/track interaction analyses. Those are derived on the basis of permissible limitations of train and track performances such as rail stress, uplift force of fastener, reduction of dynamic wheel force, and acceleration of car body. A feasible method of evaluation of track stiffness which is necessary when a designer reviews whether the criteria are satisfied or not is also presented.

• International Journal of Aeronautical and Space Sciences
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• 제6권2호
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• pp.84-96
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• 2005

Helical tip vortex is known as stable vortex structure, however the specific frequency component of far wake perturbation induces the vortex pairing in hover and axial flight. It is expected that the tip vortex pairing phenomena may happen in transition flight and very low advance ratio flight so that inflow may be most nonuniform in the low advance ratio flight. The objectives of this paper are that a tip-vortex instability during the transition from hover into very low advance ratio forward flight is numerically predicted to understand a physics by using a time-marching free-wake method. To achieve the objectives, numerical method is firstly validated in typical axial and forward flights cases. Present scheme with trim routine can predict airloads and inflow distribution of forward flight with good accuracy. Then, the transition flight condition is calculated. The rotor used in this wake calculation is a small-scale AH-1G model. By using a tip-vortex trajectory tracking method, the tip-vortex pairing process are clearly observed in transient flight($\mu$=0.03) and disappears at a slightly higher advance ratio($\mu$=0.05). According to the steady flight simulation at $\mu$=0.03, it is confirmed the tip-vortex pairing process is continued in the rear part of rotor disk and not occurs in the front part. Time averaged inflow in this case is predicted as smooth distribution.