ON THE (n, d)th f-IDEALS

Jin Guo,Tongsuo Wu 대한수학회 2015 대한수학회지 Vol.52 No.4

For a field K, a square-free monomial ideal I of K[x1, . . . , xn] is called an f-ideal, if both its facet complex and Stanley-Reisner complex have the same f-vector. Furthermore, for an f-ideal I, if all monomials in the minimal generating set G(I) have the same degree d, then I is called an (n, d)th f-ideal. In this paper, we prove the existence of (n, d)th f-ideal for d ≥ 2 and n ≥ d + 2, and we also give some algorithms to construct (n, d)th f-ideals.

Parameter identification of the phenomenological model for magnetorheological fluid dampers using hierarchic enhanced particle swarm optimization

Jin Guo,Zhendong Li,Mengxuan Zhang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.3

The magnetorheological (MR) fluid damper, as a new generation of highperformance and intelligent vibration damping devices for engineering structures, has broad application prospects in structural vibration reduction. Nonlinear hysteresis is a complex phenomenon of MR dampers. In this paper, the phenomenological model is used to simulate the dynamics of MR dampers. To accurately and efficiently identify the parameters of the phenomenological model, the hierarchical enhanced particle swarm optimization (HEPSO) algorithm is proposed. This algorithm applies a hierarchical optimization mechanism and introduces media particles to the enhanced PSO (EPSO) algorithm to improve the optimization process of parameter identification and enhance the performance of the PSO algorithm without reducing the possibility of finding the optimal solution. Compared with the standard PSO (SPSO) algorithm and the EPSO algorithm, the HEPSO algorithm has a higher efficiency, accuracy and robustness in identifying a highly nonlinear hysteretic system problem.

문법성 판단 테스트를 통해 본 중국인 학습자의 부사격 조사 ‘에’의 습득 양상

Jin Guo,김영주 서울대학교 국어교육연구소 2016 국어교육연구 Vol.37 No.-

본 연구는 중국인 중‧고급 학습자를 대상으로 부사격 조사 '에'의 습득 양상을 조사하는 것을 목적으로 한다. 이를 위해 문법성 판단 테스트를 개발하여 3∼6급의 학습자 각 30명씩 총 120명과 비교 대상으로 한국어 모어 화자 20명에게 실험을 실시하였다. 본 연구 결과, (1) 전체 중국인 학습자 집단은 매우 낮은 정답률을 보여 한국어 모어 화자와 유의미한 차이를 보였다. 이는 중국인 학습자가 부사격 조사 ‘에’의 습득에서 어려움을 겪고 있음을 나타낸다. (2) 중국인 학습자들은 ‘에의 활용’에서 가장 높은 정답률을 그리고 , ‘자격, 신분’에서 가장 낮은 정답률을 보였다. (3) 숙달도별 집단 간 조사에서 3급과 4, 5, 6급간에서 유의미한 차이가 발견되었으나 4급, 5급, 6급들 간에는 유의미한 차이가 발견되지 않았다. 이는 숙달도가 향상되어도 부사격 조사 ‘에’의 습득에 지속적인 교육적 관심이 필요함을 보여주는 결과이다. IIn this study, we carried out grammaticality judgment test of “ey,” an adverb case marker in Korean, with 120 Chinese Korean learners in the intermediate or advanced levels (level 3 to 6, 30 learners in each level) of TOPIK test, with the comparison group consisting of 20 Korean native speakers, in order to figure out acquisition aspects. In the results of the study, (1) intermediate or advanced Chinese Korean learners were able to arrive at low percentage of correct answers compared to Korean native speakers and the difference was significant in the acquisition aspects of ”ey.” (2) Acquisition aspects of “ey” were shown in the order as below. “application,” “purpose,” “recognition,” “emotion,” “arrival place,” “time,” “condition,” “situation," “price,” “setting the price,” “object,” “reason,” “cause,” “criteria for comparison,” “means,” “method,” “addition,” “place,” “location,” “qualification,” and “position.” (3) For learners among 4-6 levels in TOPIK, as their proficiency improved, no significant improvement was seen in the acquisition of “ey”; however, the only significant discrepancy was found between level 3 learners and level 4-6 learners. These results proved that instructional intervention is still necessary.

Weibull parameter estimation and reliability analysis with small samples based on successive approximation method

Jin Guo,Xiangwei Kong,Ningxiang Wu,Liyang Xie 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.11

Only few failure data can be collected because of increasing costs and reliability. Therefore, improving the estimation accuracy of Weibull distribution with small samples has become an urgent problem. In this study, a method for estimating the Weibull parameter and analyzing reliability is proposed based on the successive approximation method. In this method, the effect of sample size on the location parameter is considered to establish an iterative model of the location parameter. The iterative equations of scale and shape parameters are constructed based on the location parameter and failure data. Then, an extensive MonteCarlo simulation study is conducted to compare the performance of the proposed method with the existing methods. Simulation results show that the proposed method is superior for estimating Weibull parameters and reliability in terms of precision, robustness, and efficiency. Finally, two real examples are analyzed to illustrate the application of the proposed method.

Numerical study of rock-breaking performance of cutters in heterogeneous sand cobble ground

Jin Guo,Xiangwei Kong,Liu Cheng,Xueyi Li 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.6

Further research into tunneling performance in heterogeneous sand cobble ground demands an accurate numerical model of actual formation. In this paper, the ground model composed of spherical sand and ellipsoidal cobble was constructed to study the rockbreaking performance by using the discrete element method. The shape and physical parameters of sand and cobble were obtained on the basis of field test data. Then, the ground model was constructed to simulate the rock-breaking process of the cutterhead. The results show that the center cutter has a high flat wear percentage. With the decrease in cobble content (CC), the cracks between cutters are not connected effectively, thereby resulting in lower rock-breaking quantity. Finally, the influences of CC on the optimal parameters and crack propagation were analyzed. The results indicate that the rock-breaking performance in the ground with a low CC can be improved by increasing penetration and reducing cutter spacing.

Strong shellability of simplicial complexes

Jin Guo,Yi-Huang Shen,Tongsuo Wu 대한수학회 2019 대한수학회지 Vol.56 No.6

Imposing a strong condition on the linear order of shellable complexes, we introduce strong shellability. Basic properties, including the existence of dimension-decreasing strong shelling orders, are developed with respect to nonpure strongly shellable complexes. Meanwhile, pure strongly shellable complexes can be characterized by the corresponding codimension one graphs. In addition, we show that the facet ideals of pure strongly shellable complexes have linear quotients.

On rings whose annihilating-ideal graphs are blow-ups of a class of Boolean graphs

Jin Guo,Tongsuo Wu,Houyi Yu 대한수학회 2017 대한수학회지 Vol.54 No.3

For a finite or an infinite set $X$, let $2^X$ be the power set of $X$. A class of simple graph, called strong Boolean graph, is defined on the vertex set $2^X\setminus \{X,\,\eset\}$, with $M$ adjacent to $N$ if $M\cap N=\eset.$ In this paper, we characterize the annihilating-ideal graphs $\mathbb{AG}(R) $ that are blow-ups of strong Boolean graphs, complemented graphs and pre-atomic graphs respectively. In particular, for a commutative ring $R$ such that $\mathbb{AG}(R)$ has a maximum clique $S$ with $3\le |V(S)| \leq \infty$, we prove that $\mathbb{AG}(R)$ is a blow-up of a strong Boolean graph if and only if it is a complemented graph, if and only if $R$ is a reduced ring. If assume further that $R$ is decomposable, then we prove that $\mathbb{AG}(R)$ is a blow-up of a strong Boolean graph if and only if it is a blow-up of a pre-atomic graph. We also study the clique number and chromatic number of the graph $\mathbb{AG}(R)$.

The finite element analysis of machining characteristics of titanium alloy in ultrasonic vibration assisted machining

Dexiong Chen,Jinguo Chen,Huasen Zhou 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.8

Titanium alloy Ti6Al4V, an alpha-beta alloy, possesses many advantageous properties, such as high special strength, good resilience and resistance to high temperature and corrosion, fracture resistant characteristics and so on, being widely used in aerospace, biomedical and chemical industry. However, its machinability is still a challenge due to its low thermal conductivity, low elastic modulus and high chemical reactivity. As a novel and effective machining method, ultrasonic vibration assisted machining (UVAM) can effectively improve the machining performance of workpieces, which is widely used in the field of titanium alloy machining. A two-dimensional cutting finite element modeling methodology for orthogonal cutting titanium alloy Ti6Al4V was established to analyze the comparisons between conventional machining (CM) and ultrasonic vibration assisted machining and the effects of frequency and amplitude. The simulation results showed that (1) UVAM more easily formed serrated chip than that of CM. The chip segmentation coefficient G S which could quantitatively characterize the segmentation degree of chip showed an increasing trend with the increase of amplitude. (2) The cutting force curve of UVAM had periodic pulse fluctuation due to the effects of vibration in x-direction and y-direction. The main cutting force and the thrust force of UVAM showed the further decrease trend with the increase of frequency and x-direction amplitude. However, the y-direction amplitude made the contrary trend for the cutting force. (3) Meanwhile, with the increase of y-direction amplitude, the plastic and friction dissipation energies increased obviously. The introduction of ultrasonic vibration results in complex changes in the tool-chip contact, mechanical and temperature characteristics of the workpiece. Choosing the suitable vibration parameters will contribute to improving the machinability of titanium alloys.

Attitude Control for Astronaut Assisted Robot in the Space Station

Yangmin Li,Jinguo Liu,Qing Gao,Zhiwei Liu 제어·로봇·시스템학회 2016 International Journal of Control, Automation, and Vol.14 No.4

Because of the limited working hours of astronauts in the space station, the in-cabin robot has high valuein the technological validation and scientific research. Based on this requirement, we proposed and designed an AstronautAssisted Robot(AAR) working in the space station. It can float in the space station cabin, fly autonomously,and hold a fixed position and/or posture. In addition, it also possesses environmental awareness capabilities andintelligence. Thus the AAR can assist astronauts to complete some special scientific experiments or technical tests. In this paper, the system architecture and experimental equipment of the AAR are designed firstly depending on thecharacteristics of space microgravity environment and the requirements of assisting astronauts missions. And then,the motion principles of the AAR are analyzed and the robot’s dynamic model is established by using the Newton- Euler algorithm. Since the attitude control of the robot is the basis for its free movement, the PID Neural Network(PIDNN) algorithm, which is a kind of intelligent control algorithm, is used to design the attitude controller ofthe AAR. Finally, the reasonability of the robot’s structural design and the availability of its attitude controllers areverified through the simulation experiments.

Distance Measurement of Zooming Image for a Mobile Robot

Hongwei Gao,Jinguo Liu,Yang Yu,Yangmin Li 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.4

Aiming at the application of zooming image distance measurement to mobile robot, the related key technologies are investigated in detail in this paper. Firstly, camera parameter calibration is conducted. The camera focus, optical center displacement between two foci, principal point and aberration coefficients are calculated accurately. Then, robust feature matching based on SIFT is realized by the geometrical constraint of a zooming image. Finally, the 3D reconstruction model of zooming image is established. The experimental results based on real sample images validate the practicability of the related algorithms.