• Progress in Superconductivity and Cryogenics
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• v.6 no.1
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• pp.12-17
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• 2004

High critical current density. $J_c$ over $1MA/cm^2$ at 77 K in a self field was successfully achieved from the YBCO film prepared on (100) $SrTiO_3$ single-crystal substrates by the TFA-MOD process. Unlike a normal TFA-MOD process, we prepared the TFA precursor solution by dissolving YBCO powder into the trifluoroacetic acid. A significant amount of the second phases, including $BaF_2$, was observed in the films fired at $700-725^{\circ}C$ for 2 h under $P(O_2)=10^{-3}$ atm and $P(H_2O)=4.2%$, most probably due to an insufficient reaction time, and hence $T_c$ was greatly degraded. However the films fired at $750-800^{\circ}C$ for 2 h were composed of strongly c-axis oriented YBCO grams without any second phases. and exhibited the $T_c$ values of 89.5 ~ 91 K with a sharp transition. With increasing the firing temperature from 750 to $800^{\circ}C$ average grain size of YBCO was increased and grain connectivity was enhanced. The highest $J_c$ value of $1.1MA/cm^2$ was obtained from the YBCO film fired at $800^{\circ}C$.

• Earthquakes and Structures
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• v.26 no.5
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• pp.349-361
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• 2024

Excessive torsional behaviour is one of the major reasons for failure of buildings, as inferred from past earthquakes. Numerous seismic codes across the world specify a displacement-based or drift-based criterion for classifying buildings as torsionally irregular. In recent years, quite a few researchers have pointed out some of the inherent deficiencies associated with the current codal guidelines on torsional irregularity. This short communication paper aims to envisage the need for a revision of the displacement-based guidelines on torsional irregularity, and further highlight the appropriateness of a rotation-based criterion. A set of 6 reinforced concrete building models with asymmetric shear walls are analysed using ETABS v18.0.2, by varying the number of stories from 1 to 9, and the torsional irregularity coefficient of various stories is calculated using the displacement-based formula. Since rotation about the vertical axis is a direct indication of the twist experienced by a building, the calculated torsional irregularity coefficients of all stories are compared with the corresponding floor rotations. The conflicting results obtained for the torsional irregularity coefficients are projected through five categories, namely mismatch with floor rotations, inconsistency in trend, lack of clarity in incorporation of negative values, sensitivity to low values of displacement and error conceived in the mathematical formulation. The findings indicate that the irregularity coefficient does not accurately represent the torsional behaviour of buildings in a realistic sense. The Indian seismic code-based values of 1.2 and 1.4, which are used to characterize buildings as torsionally irregular are observed to be highly sensitive to the numerical values of displacements, rather than the actual degree of rotation. The study thus emphasizes the revision of current guidelines based on a more relevant rotation-based or eccentricity-based approach.

• Corrosion Science and Technology
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• v.4 no.4
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• pp.147-154
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• 2005

The creep resistance of geogrids is one of the most significant long-term safety characteristics used as the reinforcement in slopes and embankments. The failure of geogrids is defined as creep strain greater than 10%. In this study, the accelerated creep tests were applied to polyester geogrids at various loading levels of 30, 50% of the yield strengths and temperatures using newly designed test equipment. Also, the new test equipment permitted the creep testing at or above glass transition temperature($T_g$) of 75, 80, $85^{\circ}C$. The time-dependent creep behaviors were observed at various temperatures and loading levels. And then the creep curves were shifted and superposed in the time axis by applying time-temperature supposition principles. The shifting factors(AFs) were obtained using WLF equation. In predicting the lifetimes of geogrids, the underlying distribution for failure times were determined based on identification of the failure mechanism. The results confirmed that the failure distribution of geogrids followed Weibull distribution with increasing failure rate and the lifetimes of geogrids were close to 100 years which was required service life in the field with 1.75 of reduction factor of safety. Using the newly designed equipment, the creep test of geogrids was found to be highly accelerated. Furthermore, the time-temperature superposition with the newly designed test equipment was shown to be effective in predicting the lifetimes of geogrids with shorter test times and can be applied to the other geosynthetics.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.1
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• pp.1-9
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• 2013

This paper presents a new control algorithm for dynamic control of a unicycle robot. The unicycle robot motion consists of a pitch that is controlled by an in-wheel motor and a roll that is controlled by a reaction wheel pendulum. The unicycle robot doesn't have any actuator for a yaw axis control, which makes the derivation of the dynamics relatively simple. The Euler-Lagrange equation is applied to derive the dynamic equations of the unicycle robot to implement the dynamic speed control of the unicycle robot. To achieve the real time speed control of the unicycle robot, the sliding mode control and LQ regulator are utilized to guarantee the stability while maintaining the desired speed tracking performance. In the roll controller, the sigmoid-function based sliding mode controller has been adopted to minimize the chattering by the switching function. The LQR controller has been implemented for the pitch control to drive the unicycle robot to follow the desired velocity trajectory in real time using the state variables of pitch angle, angular velocity, angle and angular velocity of the wheel. The control performance of the two control systems form a single dynamic model has been demonstrated by the real experiments.

• Steel and Composite Structures
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• v.23 no.5
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• pp.597-610
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• 2017

This paper presents a mathematical model for fixed-end moments of I-sections with straight haunches for the general case (symmetrical and/or non-symmetrical) subjected to a concentrated load localized anywhere on beam taking into account the bending deformations and shear, which is the novelty of this research. The properties of the cross section of the beam vary along its axis "x", i.e., the flange width "b", the flange thickness "t", the web thickness "e" are constant and the height "d" varies along of the beam, this variation is linear type. The compatibility equations and equilibrium are used to solve such problems, and the deformations anywhere of beam are found by the virtual work principle through exact integrations using the software "Derive" to obtain some results. The traditional model takes into account only bending deformations, and others authors present tables considering the bending deformations and shear, but are restricted. A comparison between the traditional model and the proposed model is made to observe differences, and an example of structural analysis of a continuous highway bridge under live load is resolved. Besides the effectiveness and accuracy of the developed models, a significant advantage is that fixed-end moments are calculated for any cross section of the beam "I" using the mathematical formulas.

• The Korean Journal of Ecology
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• v.8 no.1
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• pp.1-5
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• 1985

The plastochron index (PI) provides possibility on studies of the effects of various environmental factors on morphological and physiological development of plants. The PI of Erickson and Michemlini(1957) could be used merely when leaf n is longer an leaf n+1 is smaller than the references length at any time. If both the lengths of leaf n and n+1 are smaller or longer than the reference length, it could not estimated. In this study, the PI of Erickson and Michelini was complemented and the linear patterns according to leaf arrangement was represented, PI is n-(lnLR-lnLn)/(lnLn-lnLn+1). And when both the lengths of leaf n and n+1 are longer than the length of reference, PI is n+1+(ln Ln+1-lnLR)/(lnLn-lnLn+1). The linear model of PI is changed by the various environmental factors and the linear patterns are different according to leaf arrangement. According to leaf arrangement, the equation of the general regression lines is Yin-(i-j)=a-(n-1)(q1+...+qi-1)-(q1+...+qj-1)+rt+$\varepsilon$. Where Y:the logarithmic of the leaf length in question, i:leaf number hang on the one node, n:the number counting from base, q:spacing on the Y-axis, j:0, 1, 2, ..., r:slope, t:time, $\varepsilon$:error.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.825-830
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• 2001

A numerical study on a quantitative analogy of the fully developed flow between in a straight square duct rotating about an axis perpendicular to that of the duct and a stationary curved duct of square cross-section is carried out. In order to clarify the similarity of two turbulent flows, the dimensionless parameters $K_{TR} = Re^{1/4}/\sqrt{Ro}$ and the Rossby number, Ro, in a rotating straight duct flow were used as a set corresponding to $K_{TC} = Re^{1/4}/\sqrt{{\lambda}}$ and curvature ratio, ${\lambda}$, in a stationary curved duct flow so that they have the same dynamical meaning as $K_{LR} = Re/\sqrt{Ro}$ and $K_{LC} = Re/\sqrt{{\lambda}}$ of the fully developed laminar flows. For the large values of Ro or A, it is shown that the flow field satisfies the asymptotic invariance property: there are strong quantitative similarities between the two flows such as flow patterns and friction factors for the same values of $K_L$ and $K_T$.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.307-309
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• 2004

In this study, we have evaluated and classified arthritic pathology using the auscultation of knee joint sound. Six normal persons and 11 patients with knee problem were enrolled. Six patients of Group 1 needed an orthopeadic surgery because of the ruptured wounds of meniscus or ACL(Anterior Cruciate Ligament) and 5 patients of Group 2 diagnosed as osteoarthritis. Subjects were taken knee flexion and extension being seated in a chair for 20 seconds which repeated 3 times. Also subjects stood up and sit down repeatedly in the same way. After the movement of knee was divided into 18 degrees, the pitch perturbation according to partial degrees was analyzed and the DTW(Dynamic Time Warping) method was applied for normalizing a time-axis and unpaired t-test was used for statistic results among groups. As a result, the amplitude and frequency perturbations of group 2 was higher than group 1(p<0.05) and showed a characteristic 'w-shape' in angle-amplitude graph. These results suggest that the analysis of knee joint sound might assist in early diagnosis of knee joint disease.

• Journal of the Korea Concrete Institute
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• v.12 no.2
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• pp.3-11
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• 2000

There is a possibility of poor-state concrete filling condition due to segregation and interlocking of aggregate and paste when a high performance concrete is used at reinforced concrete structure without compaction. This study was conducted to evaluate the flexural behavior of high performance concrete beams with design parameters such as c, t and different concrete filling conditions. Different concrete filling conditions were intentionally made such that the first type specimen was soundly cast to obtain the perfect concrete filling condition. Second type was cast in such a way that up to the longitudinal tensile reinforcement from the top, good concrete was filled while poor concrete was poured for the bottom part to simulate the poor strength, workability and unsatisfactory compaction. Third type was cast in such a was that up to the neutral axis of the beam section from the top, good concrete was filled while so did for the bottom part as the second type. The test results were analyzed in terms of load-displacement response, failure pattern, crack width and crack spacing. The test results indicate that have no effect of concrete filling conditions on the yielding strength of structures. But, have a grate influence on the stiffness and ductility of structures.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.336-339
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• 2003

A digital data logging system has been developed for the purpose of a compact offline Ocean Bottom Seismometer(OBS). The Digital Data Logger(DDL) consists of A/D system, Micom with storage memory and firmware managing data files. The A/D system acquires data of 16bit/4ch with sampling rate of 250Hz per channel. The Micom, a micro controller board with T33521 processor of 8051 class, was equipped with 8 flash memories of 128MB for data storage capacity of 1GB. The firmware stores the acquiring data in form of binary files. The DDL was designated to be compact and light and to consume low energy as possible. The DDL is to interface with PC through USB(Universal Serial Bus). The performance of the DDL has been validated through tests with respect to a 3-axis seismometer.