• 설비공학논문집
• /
• 제9권2호
• /
• pp.153-162
• /
• 1997

In this study, the wet surface heat transfer coefficients and friction factors of the heat exchanger with slit-wavy fin were measured. Four sample cores of two or three row with fins of 12 fpi or 16 fpi were tested. Tests were conducted in a closed loop wind tunnel, where the heat exchanger was mounted at 45 degree inclination angle. The wet surface heat transfer coefficient was reduced following the procedure given in ARI 420-81. During the course, new definitions of the $\varepsilon$-NTU applicable to enthalpy driving system were introduced. The wet surface heat transfer coefficients were approximately equal to the dry surface values. However, the friction factors were approximately 120% to 170% higher than those of the dry surface. Both the heat transfer coefficient and the friction factor of the wet surface increased as the relative humidity increased, fin pitch decreased, and the number of row decreased, although the difference was not large.

• 한국지반신소재학회논문집
• /
• 제16권4호
• /
• pp.191-210
• /
• 2017

The concern study, present the results of experimental study on the performance of deep excavation by using image processing technique particle image velocimetry (PIV). The purpose of present study is to check the application of PIV for the successive ground deformation during deep excavation. To meet the objectives of concern study, a series of reduce scale model test box experiments are performed by considering the wall stiffness, ground water table effect and ground relative density. The results are presented in form of contour and vector plots and further based on PIV analysis wall and ground displacement profile are drawn. The results of present study, indicate that, the PIV technique is useful to demonstrate the ground deformation zone during the successive ground excavation as the degree of accuracy in PIV analysis and measured results with LVDT are within 1%. Further the vector and contours plot effectively demonstrate the ground behavior under different conditions and the PIV analysis results fully support the measured results.

• 대한기계학회논문집A
• /
• 제30권4호
• /
• pp.357-363
• /
• 2006

According to the study of grasping of the human hand, it is noted that the metacarpal link of the thumb plays the key role in power grasping. Also the face of fingertip can be discriminated into five parts depending on the grasping modalities such as pinch grasp, fingertip grasp and power grasp. In this paper, the design of the anthropomorphic robot hand which has a thumb and three fingers is proposed. A difference of SKKU hand II from the previous gripperlike robot hand is that the metacarpal bone is connected between the thumb and the palm. This thumb mechanism is specially designed to get the degree of freedom which can realize flexible motions relative to objects. Based on the analysis, the hand mechanism is developed. Since the driving circuits for the hand are embedded in the hand, only the communication lines supporting CAN protocol with DC power cable are necessary as the input. A new robot is manufactured and feasibility of the hand is validated through preliminary experiments.

• 전기학회논문지
• /
• 제59권4호
• /
• pp.693-699
• /
• 2010

General transformer's life is known as paper insulation' life. If a transformer is degraded by these aging factors, it is known that electrical, mechanical and chemical characteristics for transformer's oil-paper are changed. When the kraft paper is aged, the cellulose polymer chains break down into shorter lengths. It causes decrease in both tensile strength and degree of polymerization of paper insulation. The paper breakdown is accompanied by an increase in the content of furanic compounds within the dielectric liquid. In this paper it is aimed at analysis on correlation between aging characteristics for insulating diagnosis of thermally aged paper. For investigating the accelerated aging process of oil-paper samples accelerating aging cell was manufactured for estimating variation of paper insulation during 500 hours at $140^{\circ}C$ temperature. To derive the results, it was performed analysis such as tensile strength(TS), depolymerization(DP), dielectric strength(DS), relative permittivity, water content(WC) and furan compound(FC) for aged paper. Also for analyzing correlation between insulating degradation characteristics, we used linear regression method. As as results of linear regression analysis, there was a close correlation between TS and DP. WC, FC. But dielectric strength was a weak correlation with aging time.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국제학술편); Seoul National University, Seoul; 20-22 Oct. 1993
• /
• pp.202-207
• /
• 1993

A theoretical and experimental study is presented for the force holding control of a miniature robotic ringer which is driven by a pair of piezoelectric unimorph cells. In the theoretical analysis, one finger is modeled as a flexible cantilever with a tactile force sensor at the tip and the mate of the finger is a solid beam supposed with sufficient stiffness. Further, the force sensor is modeled by a one-degree-of-freedom, mass-spring system and the output of sensor is then described by the sensor stiffness multiplied by the relative displacement. The problem investigated in this paper is that two typical holding tasks of the human finger are picked up and applied to the robotic finger. One is the work holding a stationary object with a prescribed, time-varying force and the other one is to keep the contacted force constant even if the object is in motion. The simple PID feedback control scheme is used to control the minute gripping force of order 0.01 Newton. It is shown both experimentally and theoretically that the artificial finger with the piezoelectric actuator works well in the minute force holding of the tiny object.

• Applied Biological Chemistry
• /
• 제35권3호
• /
• pp.196-201
• /
• 1992

분질 고구마인 수원 147과 점질인 황미로부터 전분을 분리하고 산가수분해 특성 및 X-ray 회절도를 통해 내부결합력 및 결정강도를 비교하였으며 겔크로마토그래피를 통해 산분해 잔사의 구조적 특성을 조사하였다. 수원 147이 황미보다 산가수분해에 강한 저항성을 보였으며 생전분의 결정화도와 산처리에 따른 전분들의 상대적 결정화도의 증가는 수원 147이 더 크게 나타났다. 산처리에 의하여 ${\beta}$-Amylolysis limit(%)는 점차 증가하였으며 겔크로마토그래피로 용출되는 분자크기가 크게 감소했다. 산분해 잔사는 중합도(DP) 25와 DP 15 부근의 2개의 peak로 분획되었다. Debranching 한 후의 분획은 DP 15부근의 단일 peak로 나타났고 peak의 DP에서 분질과 점질간 차이가 나타났다.

• Carbon letters
• /
• 제19권
• /
• pp.89-98
• /
• 2016

Taguchi’s experimental design was employed in the melt spinning of molten mesophase pitch to produce carbon fibers. The textures of the obtained carbon fibers were radial with varied crack angles, as observed by scanning electron microscopy and polarized optical imaging. The diameter, crack angle, preferred orientation, and tensile modulus of the produced samples were examined to investigate the influence of four spinning variables. The relative importance of the variables has been emphasized for each characteristic. The results show that thicker carbon fiber can be obtained with a smaller entry angle, a higher spinning temperature, a reduced winding speed, and an increased extrusion pressure. The winding speed was found to be the most significant factor in relation to the fiber diameter. While it was observed that thicker carbon fiber generally shows improved preferred orientation, the most important variable affecting the preferred orientation was found to be the entry angle. As the entry angle decreased from 120° to 60°, the shear flow was enhanced to induce more ordered radial alignment of crystallite planes so as to obtain carbon fibers with a higher degree of preferred orientation. As a consequence, the crack angle was increased, and the tensile modulus was improved.

• Journal of Oral Medicine and Pain
• /
• 제23권1호
• /
• pp.45-55
• /
• 1998

The author assessed the sagittal relationships between glenoid fossa of the temporal bone and mandibular condyle from lateral transcranial views of 74 TMJ with disc displacement and 16 TMJ with normal disc-condyle complex by the magnetic resonance image findings. All the subjects were female and also in their 3rd decades. The disc displacement group was subdivided into anterior disc displacement with reduction (ADWR) group and anterior disc displacement without reduction (ADWOR) group. The anterior, superior, and posterior joint spaces as well as anterior/posterior (A/P) ratio of the space at the closed jaw position and vertical and horizontal components of the condyle position relative to the articular eminence at the open jaw position were measured from all the subjects and the data were compared among groups. The result were as follows : 1. The mean posterior joint space of ADWR group was smaller than ADWOR group, but there were no significant differences in anterior and superior joint spaces between two groups. 2. There showed a tendency of higher A/P ratio in ADWR group which meant the condyle of ADWR was likely to take posteriorly displaced position. 3. There were higher proportion of neutral condylar position in glenoid fossa in normal group, but higher proportion of posterior condylar position in ADWR group. 4. There were no significant differences in the degree of condyle-fossa concentricity among groups.

• 천문학회지
• /
• 제44권2호
• /
• pp.59-65
• /
• 2011

A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles that are well-fitted by a relativistic accretion disk model. We develop a Monte Carlo code to compute the linear polarization of a double peaked broad emission line arising from Thomson scattering. A Keplerian accretion disk is adopted for the double peak emission line region and the geometry is assumed to be Schwarzschild. Far from the accretion disk where flat Minkowski geometry is appropriate, we place an azimuthally symmetric scattering region in the shape of a spherical shell sliced with ${\Delta}{\mu}=0.1$. Adopting a Monte Carlo method we generate line photons in the accretion disk in arbitrary directions in the local rest frame and follow the geodesic paths of the photons until they hit the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the degree of linear polarization also shows a double peak structure. Under favorable conditions we show that up to 0.6% linear polarization may be obtained. We conclude that spectropolarimetry can be a powerful probe to reveal much information regarding the accretion disk geometry of these active galactic nuclei.

• Asian-Australasian Journal of Animal Sciences
• /
• 제28권3호
• /
• pp.323-327
• /
• 2015

Wattle length, width, and area were measured to classify bilateral asymmetries in four lines of chickens. The lines were the S26 generation of White Leghorns selected for high (HAS) or low (LAS) response to sheep red blood cells and sublines in which selection had been relaxed for three generations (high antibody relaxed [HAR] and low antibody relaxed [LAR]). Antibody titers (AB) were greater for HAS than for HAR with both greater than for LAS and LAR which while different for males did not differ for females. The low antibody lines were heavier and reached sexual maturity at younger age than the high antibody lines. In general, wattle length, width, and area were greater in the low than high antibody lines. In 24 comparisons for bilaterality 18 exhibited fluctuating asymmetry and 6 exhibited directional asymmetry with 5 of the 6 being for wattle length. There was not a clear pattern for changes in degree of asymmetry when selection was relaxed for 3 generations. For females, the relative asymmetry (RA) of wattle area was larger ($p{\leq}0.05$) for HAR than for LAR and not different from the selected lines and relaxed lines. There were no differences among lines for RA of wattle length and width of females and wattle length, width, and area of males.