• 한국방사선학회논문지
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• 제15권1호
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• pp.9-14
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• 2021

방사선에 의한 피폭 없이 대조도가 우수한 영상의 획득이 가능한 자기공명영상은 진단에 필수적이지만 영상에서의 노이즈 발생은 불가피한 요소이기 때문에 이를 보완하기 위해 자기공명영상장치의 변수들을 조절하여 우수한 특성을 가진 영상을 획득할 수 있다. 이 중, 여기횟수 (NEX; number of excitation)는 추가적인 영상 특성의 저하 없이 우수한 특성의 영상을 획득할 수 있지만 scan time이 증가하여 motion artifact를 발생시킬 수 있고, scan time의 증가에 비례하여 영상의 특성이 향상되지 않기 때문에 적절한 NEX의 설정이 필요하다. 따라서, 본 연구에서는 MRiLab simulation program을 통해 자기공명영상의 모든 변수들을 고정시킨 후, NEX만을 조절하여 획득한 뇌 T2 강조 영상의 정량적 평가를 통해 NEX 변화에 따른 영상 특성의 경향성을 평가하고자 하였다. 획득한 영상의 노이즈 레벨 및 유사도 평가를 하기 위해 신호 대 잡음비 (SNR; signal to noise ratio), 대조도 대 잡음비 (CNR; contrast to noise ratio), 평균 제곱근 오차 (RMSE; root mean square error) 그리고 최대 신호 대 잡음비 (PSNR; peak signal to noise ratio)를 계산하였다. 결과적으로, 노이즈 레벨 및 유사도 평가 인자 모두 NEX가 증가함에 따라 개선된 값을 보였으나, 점차 증가폭이 감소함을 보였다. 따라서, 과도하게 큰 NEX는 장시간의 scan에 따른 motion artifact를 발생시켜 영상 특성을 저하시킬 수 있으므로, 적절한 NEX의 설정이 중요함을 확인하였다.

• 대한치과보철학회지
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• 제28권1호
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• pp.137-163
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• 1990

The properties of a investment material can be described by the consistency at the slurry state, the setting time, the compressive strength and the thermal expansion during the casting. In this study the effect of the production parameters which are included the ratio of quartz and cristobalite, the content of binder, the water powder ratio and the content and concentration of additives on the Properties of the gypsum-bonded investments has been investigated with help of the consistency test, the vicat needle test, the compressive strength test, the thermal expansion test, x-ray diffraction and DTA thermal differential test. The experimental results showed that the constitution of a investment with W/P ratio of 0.34, 30% of gypsum, 0.8% aluminium sulfate, 2% magnesium sulfate, 0.6% sodium phosphate was adapted for the properties of the KDA Spec. No. 13 type I investment. The important experimental results are summarized as follows. 1. The consistency of the investment decreased with increasing amount of aluminium sulfate and decreasing amount of sodium phosphate. An addition of magnesium sulfate up to 2% an increase of the consistency was shown. But 3% magnesium sulfate in investment showed a decrease of the consistency. The consistency did not vary significantly with a variation of the content of gypsum and cristobalite and the W/P ratio. 2. Aluminium sulfate and the magnesium sulfate promoted the hardening and the aluminium phosphate delayed the hardening. The setting time increased with amount of gypsum. The effect of the matrix on the setting time was insignificant. With the W/P ratio of 0.34 the setting time was 14 min. 3. The compressive strength decreased with the amount of aluminium sulfate up to 0.25% and increased with the amount of aluminium sulfate greater than 3%. The compressive strength decreased as decreasing the amount of magnesium sulfate and gypsum and as increasing the W/P ratio. The effect of the refractory on the compressive strength was also not significant. With the W/P ratio of 0.34 the compressive strength was $34Kg/mm^2$. 4. The 1st thermal expansion was found at the temperature near and the steady state or the contraction stage was found at the temperature between $250^{\circ}C$ and $500^{\circ}C$. After this stage the 2nd thermal expansion took place at the temperature near $500^{\circ}C$. The amount of thermal expansion increased with decreasing the content of magnesium sulfate, aluminium sulfate and gypsum and the W/P ratio. And the amount of thermal expansion increased as the content of sodium phosphate and cristobalite. With the W/P ratio of 0.34 the amount of total expansion was 1.2%.

• 대한치과보철학회지
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• 제29권1호
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• pp.139-165
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• 1991

The properties of a investment material can be described by the consistency at the slurry state, the setting time, the compressive strength and the thermal expansion during the casting. In this study the effect of the production parameters which are included the ratio of quartz and cristobalite, the content of binder, the water powder ratio and the content and concentration of additives on the properties of the gypsum-bonded investments has been investigated with help of the consistency test, the vicat needle test, the compressive strength test, the thermal expansion test, x-ray diffraction and DTA thermal differential test. The experimental results showed that the constitution of a investment with W/P ratio of 0.34, 30% of gypsum, 0.8% aluminium sulfate, 2% magnesium sulfate, 0.6% sodium phosphate was adapted for the properties of the KDA Spec. No. 13 type I investment. The important experimental results are summarized as follows. 1. The consistency of the investment decreased with increasing amount of aluminium sulfate and decreasing amount of sodium phosphate. An addition of magnesium sulfate up to 2% an increase of the consistency was shown. But 3% magnesium sulfate in investment showed a decrease of consistency. The consistency did not vary significantly with a variation of the content of gypsum and cristobalite and the W/P ratio. 2. Aluminium sulfata and the magnesium sulfate promoted the hardening and the aluminium phoshpate delayed the hardening. The setting time increased with amount of gypsum. The effect of the matrix on the setting time was insignificant. With the W/P ratio of 0.34 the setting time was 14 min. 3. The compressive strength decreased with the amount of aluminium sulfate up to 0.25% and increased with the amount of aluminium sulfate greater than 3%. The compressive strength decreased as decreasing the amount of magnesium sulfate and gypsum and as increasing the W/P ratio. The effect fo the refractory on the compressive strength was also not significant. With the W/P ratio of 0.34 the compressive strength was $34Kg/mm^2$. 4. The 1st thermal expansion was found at the temperature near $250^{\circ}C$ and the steady state or the contraction stage was found at the temperature between $250^{\circ}C$ and $500^{\circ}C$. After this stage the 2nd thermal expansion took place at the temperature near $500^{\circ}C$. The amount of thermal expansion increased with decreasing the content of magnesium sulfate, aluminium sulfate and gypsum and the W/P ratio. And the amount of thermal expansion increased as the content of sodium phosphate ad cristobalite. With the W/P ratio of 0.34 the amount of total expansion was 1.2%.

• Interaction and multiscale mechanics
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• 제5권3호
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• pp.211-228
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• 2012

This paper reports the development of a generalized inverse analysis formulation for the parameter estimation of four-parameter Burger model. The analysis is carried out by formulating the problem as a mathematical programming formulation in terms of identification of the design vector, the objective function and the design constraints. Thereafter, the formulated constrained nonlinear multivariable problem is solved with the aid of fmincon: an in-built constrained optimization solver module available in MatLab. In order to gain experience, a synthetic case-study is considered wherein key issues such as the determination and setting up of variable bounds, global optimality of the solution and minimum number of data-points required for prediction of parameters is addressed. The results reveal that the developed technique is quite efficient in predicting the model parameters. The best result is obtained when the design variables are subjected to a lower bound without any upper bound. Global optimality of the solution is achieved using the developed technique. A minimum of 4-5 randomly selected data-points are required to achieve the optimal solution. The above technique has also been adopted for real-time settlement of four oil refineries with encouraging results.

• The Journal of Korean Physical Therapy
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• 제32권3호
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• pp.185-190
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• 2020

Purpose: Gait and cognitive impairment in stroke patients exacerbate fall risk and mobility difficulties during multi-task walking. Virtual reality can provide interesting and challenging training in a community setting. This study evaluated the effect of community-based virtual reality gait training (VRGT) using a 360-degree image on the gait ability of chronic stroke patients. Methods: Forty-five chronic stroke patients who were admitted to a rehabilitation hospital participated in this study. Patients meeting the selection criteria were randomly divided into a VRGT group (n=23) and a control group (n=22). Both these groups received general rehabilitation. The VRGT group was evaluated using a 360-degree image that was recorded for 50 minutes a day, 5 days per week for a total of 6 weeks after their training. The control group received general treadmill training for the same amount of time as that of the VRGT group. The improvement in the spatiotemporal parameters of gait was evaluated using a gait analyzer system before and after training. Results: The spatiotemporal gait parameters showed significant improvements in both groups compare with the baseline measurements (p<0.05), and the VRGT group showed more improvement than the control group (p<0.05). Conclusion: Community-based VRGT has been shown to improve the walking ability of chronic stroke patients and is expected to be used in rehabilitation of stroke patients in the future.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2178-2186
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• 2018

Online identification of load parameters is the premise of establishing a stable and highly-efficient ICPT (Inductive Coupled Power Transfer) system. However, compared with pure resistive load, precise identification of composite load, such as resistor-inductance load and resistance-capacitance load, is more difficult. This paper proposes a method for detecting the composite load parameters of ICPT system utilizing harmonics. In this system, the fundamental and harmonic wave channel are connected to the high frequency inverter jointly. The load parameter values can be obtained by setting the load equation based on the induced voltage of secondary-side network, the fundamental wave current, as well as the third harmonic current effective value received by the secondary-side current via Fourier decomposition. This method can achieve precise identification of all kinds of load types without interfering the normal energy transmission and it can not only increase the output power, but also obtain higher efficiency compared with the fundamental wave channel alone. The experimental results with the full-bridge LCCL-S type voltage-fed ICPT system have shown that this method is accurate and reliable.

• Environmental Engineering Research
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• 제23권2호
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• pp.175-180
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• 2018

Box-Behnken Design (BBD) under response surface methodology (RSM) was implemented to optimization the operating parameters and assess the removal and recovery efficiencies of crude oil from contaminated soil using subcritical water extraction. The effects of temperature, extraction time and water flow rate were explored, and the results indicate that temperature has a great impact on crude oil removal and recovery. The correlation coefficients for oil removal ($R^2=0.74$) and recovery ($R^2=0.98$) suggest that the proposed quadratic model is useful. When setting the target removal and recovery (>99%), BBD-RSM determined the optimum condition to be a temperature of $250^{\circ}C$, extraction time of 120 min, and water flow rate of 1 mL/min. An experiment was carried out to confirm the results, with removal and recovery efficiencies of 99.69% and 87.33%, respectively. This result indicates that BBD is a suitable method to optimize the process variables for crude oil removal and recovery from contaminated soil.

• 대한산업공학회지
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• 제39권5호
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• pp.361-366
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• 2013

Prediction of process parameters is very important in parameter design. If predictions are fairly accurate, the quality improvement process will be useful to save time and reduce cost. The concept of dual response approach based on response surface methodology has widely been investigated. Dual response approach may take advantages of optimization modeling for finding optimum setting of input factor by separately modeling mean and variance responses. This study proposes an alternative dual response approach based on machine learning techniques instead of statistical analysis tools. A hybrid neural network-genetic algorithm has been proposed for the purpose of parameter design. A neural network is first constructed to model the relationship between responses and input factors. Mean and variance responses correspond to output nodes while input factors are used for input nodes. Using empirical process data, process parameters can be predicted without performing real experimentations. A genetic algorithm is then applied to find the optimum settings of input factors, where the neural network is used to evaluate the mean and variance response. A drug formulation example from pharmaceutical industry has been studied to demonstrate the procedures and applicability of the proposed approach.

• Smart Structures and Systems
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• 제14권5호
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• pp.831-845
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• 2014

This paper proposed a discrete wavelet transform based method for time-varying physical parameter identification of shear type structures. The time-varying physical parameters are dispersed and expanded at multi-scale as profile and detail signal using discrete wavelet basis. To reduce the number of unknown quantity, the wavelet coefficients that reflect the detail signal are ignored by setting as zero value. Consequently, the time-varying parameter can be approximately estimated only using the scale coefficients that reflect the profile signal, and the identification task is transformed to an equivalent time-invariant scale coefficient estimation. The time-invariant scale coefficients can be simply estimated using regular least-squares methods, and then the original time-varying physical parameters can be reconstructed by using the identified time-invariant scale coefficients. To reduce the influence of the ill-posed problem of equation resolving caused by noise, the Tikhonov regularization method instead of regular least-squares method is used in the paper to estimate the scale coefficients. A two-story shear type frame structure with time-varying stiffness and damping are simulated to validate the effectiveness and accuracy of the proposed method. It is demonstrated that the identified time-varying stiffness is with a good accuracy, while the identified damping is sensitive to noise.

• Journal of information and communication convergence engineering
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• 제15권2호
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• pp.97-103
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• 2017

Implementation of faster pairing calculation is the basis of efficient pairing-based cryptographic protocol implementation. Generally, pairing is a costly operation carried out over the extension field of degree $k{\geq}12$. But the twist property of the pairing friendly curve allows us to calculate pairing over the sub-field twisted curve, where the extension degree becomes k/d and twist degree d = 2, 3, 4, 6. The calculation cost is reduced substantially by twisting but it makes the discrete logarithm problem easier if the curve parameters are not carefully chosen. Therefore, this paper considers the most recent parameters setting presented by Barbulescu and Duquesne [1] for pairing-based cryptography; that are secure enough for 128-bit security level; to explicitly show the quartic twist (d = 4) and sextic twist (d = 6) mapping between the isomorphic rational point groups for KSS (Kachisa-Schaefer-Scott) curve of embedding degree k = 16 and k = 18, receptively. This paper also evaluates the performance enhancement of the obtained twisted mapping by comparing the elliptic curve scalar multiplications.