Influence of carbonitriding on microstructure, residual stress and mechanical properties of graded cemented carbides

Man Feng Gong,Jian Chen,Qiang Guo Jiang,Shang Hua Wu 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.3

The influences of carbonitriding treatment on the microstructure, residual stress and mechanical properties of Ti-containingcemented carbides are investigated. Three powder compacts of WC-7.0Co-2.0Ni-3.0Mo-0.5TiC cemented carbides were liquidphase sintered in vacuum at 1,300 oC for 1h. Three specimens with cobalt-enriched surface layers were obtained. They weresubsequently carbonized by a post-sintering heat treatment process in nitrogen. The carbonitriding treatment results in theformation of fine-grained TiN phases and N-diamond C phases in situ on their surfaces. X-ray diffraction spectrums revealtheir differences in the grain size and forming phases of the Ti-containing phases for cemented carbides before and aftercarbonitriding treatment. This method can reduce the grain size of Ti-containing hard phase and increase microstrains in it. To analyze the residual stress, the specimen before and after carbonitriding was measured by recording the peak positions foreach 2θ at five different tilt angles (ψ = 0 o,20.7 o, 30 o, 37.8 oand 45 o) by a X-ray diffractometer. The microstructure anddefects of cemented carbides were investigated by SEM before and after the carbonitriding treatment. It is concluded that:(1) high bond strength between the Ti-containing skin and the WC-Co substrate, (2) high wear resistance of the Ti-containing skinafter carbonitriding, (3) compression stress state existing in Ti-containing skin, (4) the technology of carbonitriding treatmentcontributes to form an aesthetic Ti-containing skin in the surface of cemented carbides and improve its wear resistance.

Dual-Responsive Shape Memory and Thermally Reconfigurable Reduced Graphene Oxide-Vitrimer Composites

Guo-kang Chen,Kun Wu,Qian Zhang,Yan-cen Shi,Man-geng Lu 한국고분자학회 2019 Macromolecular Research Vol.27 No.6

In this paper, we have prepared shape memory reduced graphene oxidevitrimer composites via in situ reduction of graphene oxide (GO) during the curing reaction. Because of good compatibility between GO and epoxy resin, reduced graphene oxide (rGO) has a good dispersion in the epoxy matrix. Conventional thermoset shape memory polymers can only maintain one permanent shape, while these obtained composites can be randomly reconfigured into other shapes via dynamic covalent transesterification reaction at 200 °C above transesterification temperature (TV). They can recover quickly from fixed shapes to their initial shapes with shape fixity ratio higher than 95% and shape recovery ratio higher than 97%. Besides, the rGO-vitrimers show good mechanical properties and thermal stabilities. In addition, sequent nearinfrared (NIR) irradiation can control the shape recovery, because rGO can serve as an energy convertor to convert NIR irradiation into thermal energy.

친환경 쇼핑 및 식당 환경을 위한 새로운 서비스 디자인 만기

Guo Haoyue,Cho Man Soo,Pan Younghwan 한국서비스디자인학회 2019 한국서비스디자인학회 학술대회자료집 Vol.2019 No.2

A new non-randomized multi-category response model for surveys with a single sensitive question: Design and analysis

Man-Lai Tang,Guo-Liang Tian,Nian-Sheng Tang,Zhenqiu Liu 한국통계학회 2009 Journal of the Korean Statistical Society Vol.38 No.4

In this article, we develop a non-randomized multi-category response model for a single sensitive survey question with multiple outcomes. Unlike existing randomized response models, our proposed model does not require any randomizing device and the respondents are merely asked to answer a non-sensitive question. It thus reduces cost, ensures reproducibility of respondents' answer (i.e., the same respondent gives the same answer if the survey is re-conducted under the non-randomized multi-category model), enhances respondents' trust on the privacy policy, and motivates respondents' cooperation. We show maximum likelihood estimates (MLEs) of cell probabilities can be obtained in closed- form. Bootstrap standard errors and confidence intervals (CIs) of the cell probabilities or their functions are then given. Bayesian estimation via the data augmentation algorithm is developed when prior information on the parameters of interest is available. Simulation studies are conducted to evaluate the performance of the MLEs and CI estimates. A real data set from a questionnaire on sexual activities in Korean adolescents is used to illustrate the proposed design and analysis methods.

Antagonism of PPAR-γ signaling expands human hematopoietic stem and progenitor cells by enhancing glycolysis

Guo, Bin,Huang, Xinxin,Lee, Man Ryul,Lee, Sang A,Broxmeyer, Hal E Nature Publishing Group 2018 Nature medicine Vol. No.

Hematopoietic stem cells (HSCs) quiescently reside in bone marrow niches and have the capacity to self-renew or differentiate to form all of the blood cells throughout the lifespan of an animal. Allogeneic HSC transplantation is a life-saving treatment for malignant and nonmalignant disorders. HSCs isolated from umbilical cord blood (CB) are used for hematopoietic cell transplantation (HCT), but due to the limited numbers of HSCs in single units of umbilical CB, a number of methods have been proposed for ex vivo expansion of human HSCs. We show here that antagonism of peroxisome proliferator-activated receptor (PPAR)-γ promotes ex vivo expansion of phenotypically and functionally defined subsets of human CB HSCs and hematopoietic progenitor cells (HSPCs). PPAR-γ antagonism in CB HSPCs strongly downregulated expression of several differentiation-associated genes, as well as fructose-bisphosphatase 1 (FBP1; which encodes a negative regulator of glycolysis), and enhanced glycolysis without compromising mitochondrial metabolism. The expansion of CB HSPCs by PPAR-γ antagonism was completely suppressed by removal of glucose or inhibition of glycolysis. Moreover, knockdown of FBP1 expression promoted glycolysis and ex vivo expansion of long-term repopulating CB HSPCs, whereas overexpression of FBP1 suppressed the expansion of CB HSPCs that was induced by PPAR-γ antagonism. Our study suggests the possibility for a new and simple means for metabolic reprogramming of CB HSPCs to improve the efficacy of HCT.

Strength and Mechanism of Carbonated Solidified Clay with Steel Slag Curing Agent

Man Li,Qiang Wang,Jingdong Yang,Xiaoliang Guo,Wenjun Zhou 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.3

Industrial wastes, such as steel slag and desulfurized gypsum, are piled up in large quantities and only a very small portion is recycled, adversely impacting natural ecosystems. Meanwhile, environmental problems caused by CO2 have increasingly received attention. Hence, this study introduces a novel environmentally friendly composite, formed by sodium hydroxide (used as an activator), desulfurized gypsum and steel slag (S-GS). The main objective of this study is to evaluate the potential use of S-GS for solidifying clay under the condition of carbonation curing. Besides, the samples’ characteristics are investigated according to the tests of unconfined compressive strength (UCS), pH, carbonation depth, quality loss and scanning electron microscope (SEM). It is found that the UCS of solidified clay decreases with the increasing water content while it increases first and then decreases with the increasing desulfurized gypsum content, reaching the maximum when the water content is 0.5 times the liquid limit and the content of desulfurized gypsum is 8%. Moreover, compared with the standard curing, carbonation curing can stimulate the activity of S-GS to improve the UCS of samples more effectively. With the increasing carbonation curing time, the mass loss rate and carbonation depth of samples increase while the pH value decreases. Additionally, based on the normalized analysis, the carbonation time has the most significant effect on the UCS. Furthermore, the SEM results indicate that formation of Calcium carbonate and Magnesium carbonate are primary reasons for improving the UCS of the stabilised clay during carbonization. This research promotes steel slag and desulfurized gypsum as green stabilisers for soil stabilization, and the method of carbonation curing contributes to the higher UCS, which also greatly shortens the curing time.

Nonlinear aerostatic stability analysis of Hutong cable-stayed rail-cum-road bridge

Man Xu,Weiwei Guo,He Xia,Kebing Li 한국풍공학회 2016 Wind and Structures, An International Journal (WAS Vol.23 No.6

To investigate the nonlinear aerostatic stability of the Hutong cable-stayed rail-cum-road bridge with ultra-kilometer main span, a FEM bridge model is established. The tri-component wind loads and geometric nonlinearity are taken into consideration and discussed for the influence of nonlinear parameters and factors on bridge resistant capacity of aerostatic instability. The results show that the effect of initial wind attack-angle is significant for the aerostatic stability analysis of the bridge. The geometric nonlinearities of the bridge are of considerable importance in the analysis, especially the effect of cable sag. The instable mechanism of the Hutong Bridge with a steel truss girder is the spatial combination of vertical bending and torsion with large lateral bending displacement. The design wind velocity is much lower than the static instability wind velocity, and the structural aerostatic resistance capacity can meet the requirement.

Experimental research on seismic behavior of a composite RCS frame

Jinjie Men,Yarong Zhang,Zhifeng Guo,Qingxuan Shi 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.4

To promote greater acceptance and use of composite RCS systems, a two-bay two-story frame specimen with improved composite RCS joint details was tested in the laboratory under reversed cyclic loading. The test revealed superior seismic performance with stable load versus story drift response and excellent deformation capacity for an inter-story drift ratio up to 1/25. It was found that the failure process of the frame meets the strong-column weak-beam criterion. Furthermore, cracking inter-story drift ratio and ultimate inter-story drift ratio both satisfy the limitation prescribed by the design code. Additionally, inter-story drift ratios at yielding and peak load stage provide reference data for Performance-Based Seismic Design (PBSD) approaches for composite RCS frames. An advantage over conventional reinforced concrete and steel moment frame systems is that the displacement ductility coefficient of the RCS frame system is much larger. To conclude, the test results prove that composite RCS frame systems perform satisfactorily under simulated earthquake action, which further validates the reliability of this innovative system. Based on the test result, some suggestions are presented for the design of composite RCS frame systems.

Experimental research on seismic behavior of novel composite RCS joints

Jinjie Men,Zhifeng Guo,Qingxuan Shi 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.1

Results from an experimental study on the seismic response of six composite reinforced concrete column-to-steel beam interior joints are presented. The primary variable investigated is the details in the joint. For the basic specimen, the main subassemblies of the beam and column are both continuous, and the steel beam flanges extended to the joint are partly cut off. Transverse beam, steel band plates, cove plates, X shape reinforcement bars and end plates are used in the other five specimens, respectively. After the joint steel panel yielded, two failure modes were observed during the test: local failure in Specimens 1, 2 and 4, shear failure in Specimens 3, 5 and 6. Specimens 6, 3, 5 and 4 have a better strength and deformation capacity than the other two specimens for the effectiveness of their subassemblies. For Specimens 2 and 4, though the performance of strength degradation and stiffness degradation are not as good as the other four specimens, they all have excellent energy dissipation capacity comparing to the RC joint, or the Steel Reinforced Concrete (SRC) joint. Based on the test result, some suggestions are presented for the design of composite RCS joint.

중국기업의 기업윤리가 경쟁우위에 미치는 영향에 관한 연구

장국위(Guo-Wei ZHANG),이상만(Sang-Man LEE) 전북대학교 산업경제연구소 2012 아태경상저널 Vol.4 No.1

본 연구는 중국 기업에 있어서 기업윤리가 기업의 경영성과에 미치는 영향 중 특별히 기업윤리의 수준이 비용우위와 차별화우위를 통한 경쟁우위의 수준에 미치는 영향을 확인하는데 목적을 두고 있다. 특히 기업윤리와 경쟁우위의 관계에서 기업규모가 조절효과를 가지는지를 분석하였다. 분석결과 첫째, 기업윤리의 결정요인들 중 기업경영자의 개인적 요인, 조직적 요인 및 사회적 요인 모두가 기업의 비용우위에 유의적인 정(+)의 영향을 미치는 것으로 확인되었다. 둘째, 기업윤리의 결정요인들 중기업경영자의 개인적 요인, 조직적 요인 및 사회요인은 기업의 차별화우위에 유의적인 정(+)의 영향을 미치는 것으로 확인되었다. 마지막으로 기업규모(대기업과 중소기업)는 기업윤리와 차별화우위의 관계에 대해서는 완전한 조절효과를 가지는 것으로 나타난 반면, 기업윤리와 비용우위간의 관계에 대해서는 부분적인 조절효과를 가지는 것으로 나타났다. 이러한 연구결과는 앞으로 중국기업들을 대상으로 한 연구에서 유용한 지침이 될 것으로 기대된다. The purpose of this study is to see if business ethics affects the competitive advantage of the firms. It distinguishes itself from most of the previous studies in that it focuses on Chinese businesses as units of analysis, rather than Korean businesses. Another distinction is it uses the competitive advantages of the firms as dependent variables instead of management performance. The results of the empirical research are as follows. All the three independent variables such as individual factors, organizational factors and social factors, which compose the dimension of business ethics, have significant effects both on cost advantages and differentiation advantages. In addition, the firm size has a moderating effect on the relationship between business ethics and cost advantages, while it has a moderating effect in part on the relationship between business ethics and differentiation advantages.