Influence of Cu Content on the Microstructure, Mechanical, and Tribological Properties of ZrN–Cu Films

Tong Chen,Lihua Yu,Hongbo Ju,Junhua Xu,Shinji Koyama 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2018 NANO Vol.13 No.4

A series of ZrN–Cu nano-composite films were deposited using the RF magnetron sputtering system. The microstructure, mechanical properties and tribological properties were investigated. The results showed that ZrN–Cu films were composed of face-centered cubice (fcc)-ZrN and face-centered cubic (fcc)-Cu. With the increase of Cu content, the hardness of ZrN–Cu composite film increased slowly first and then decreased rapidly. The maximum hardness value was 34.6 GPa at 16 at.% Cu. At room temperature, the coefficient of friction (Cof.) of ZrN–Cu films were lower than the ZrN film. When the content of Cu was lower than 39 at.%, the wear rate of ZrN–Cu films were lower than the ZrN film. When the temperature of tribological testing was between 200–700 ℃, the Cof. of ZrN–Cu films at 16 at.% Cu were lower than ZrN film, while the wear rates were higher than the ZrN film. In summary, the addition of Cu improved the hardness and tribological properties of the ZrN–Cu film at room temperature, and decreased the Cof. of the ZrN-Cu during 200–700 ℃.

Characterization of the dynamic change of microRNA expression in mice hypothalamus during the time of female puberty

Gideon Omariba,Li Tong,Maochun Wang,Kai Li,Yuxun Zhou,Junhua Xiao 한국유전학회 2018 Genes & Genomics Vol.40 No.3

Puberty onset is a milestone in sexual development. A tumor suppress gene (TSG) network had been reported to be involved in the regulation of female puberty onset. The observations in rodents and primates showed a potential link between microRNAs and puberty onset. To figure out what miRNAs play roles in this important biological process, profilings of microRNAs in the hypothalamus of female mice from three different pubertal stages, juvenile [postnatal day (P10)], early pubertal (P25) and pubertal (P30) were performed on the Affymetrix GeneChip miRNA 3.0 Arrays, the cerebral cortex (CTX) was used as a control tissue. 20 miRNAs were shown to be differentially expressed in hypothalamus (fold change > 1.5, P < 0.05), but not in CTX during the transition from juvenile to pubertal. Four of them were validated by real-time quantitative RT-PCR (qRTPCR) method. 1018 genes were predicted as the targets of these miRNAs. Further bioinformatics analysis suggested that these target genes were involved in many important signaling pathways, especially in the cancer related pathways. We also found that about 90% of these target genes were expressed in the hypothalamus, as well as in the immortalized GnRH-producing GT1-7 cells, which provided additional evidence that these miRNAs could be female puberty onset related. Here we present a novel comprehensive data set of miRNA gene expression during the puberty onset; and it provides an important recourse for the future functional characterization of individual miRNAs and their targets in mouse hypothalamus and in GT1-7 cells.

Tex3: An 2R1T Parallel Manipulator with Minimum DOF of Joints and Fixed Linear Actuators

Lingmin Xu,Qinchuan Li,Junhua Tong,Qiaohong Chen 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.2

A new 2R1T (R: rotation, T: translation) parallel manipulator (PM), called Tex3, is proposed. The Tex3 PM is a 2PUR-PRU PM consisting of 9 joints with 12 DOFs (degrees of freedom), and can be actuated by fixed linear actuators. Mobility analysis shows that it is an RPR-equivalent PM whose finite motion is the product of a rotation (R) followed by a translation (P) and another rotation (R). Inverse position and velocity analyses are discussed. Furthermore, the local transmission index and good transmission workspace are used to evaluate the motion/force transmissibility of the proposed PM. The singularity loci of the proposed PM are obtained according to the motion/force transmissibility, corresponding to the inverse, forward and combined kinematic singularity. The constraint singularity is also discussed. Finally, link parameters are optimized to obtain an improved good transmission workspace. Because of its minimum DOF of joints and fixed linear actuators, the Tex3 PM has good kinematic performance and is suited to the high-speed machining of workpieces with curved surfaces.

Elastostatic Stiffness Analysis of a 2PUR-PSR Overconstrained Parallel Mechanism

Chao Yang,Qiaohong Chen,Junhua Tong,Qinchuan Li 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.4

The elastostatic stiffness performance of a 2PUR-PSR (S: spherical joint; U: universal joint; R: revolute joint; P: prismatic pair) overconstrained parallel mechanism with two rotational and one translational (2R1T) degrees of freedom was studied based on screw theory and strain energy. First, the actuator and constraint wrenches of the mechanism were obtained based on screw theory. Second, by considering the space composite elastic deformation of the rod (including axial tension, and shear, torsional and bending deformation), compact limb stiffness matrixes were obtained in terms of strain energy and Castigliano’s second theorem. Finally, analytic expressions for the overall stiffness matrix of the mechanism and the amplitudes of the actuator and constrained wrenches were obtained based on the virtual-work principle and the balance equation for a moving platform. The relative error between results from the analytical model and the Workbench finite element model is approximately 1.3%, which validates the effectiveness of the proposed elastostatic stiffness model. Unlike traditional stiffness evaluation index, a regional stiffness index was proposed to measure the mechanism’s stiffness performance at various working heights. Using the index, it is possible to determine the optimum stiffness region of a moving platform with known external wrenches.

A Multiplex Sensitive Quantification of MicroRNAs Based on Competitive PCR

Maochun Wang,Li Tong,Sijia Wang,Kai Li,Junhua Xiao,Yuxun Zhou 한국생물공학회 2017 Biotechnology and Bioprocess Engineering Vol.22 No.1

MicroRNAs (miRNAs) are endogenous ~22 nt RNAs that play important regulatory roles in animals and plants by targeting mRNAs for cleavage or gene silencing. Although quantitative real-time PCR (qRT-PCR) had been widely used for miRNAs quantification, a multiplex quantification method is demanding. In this study, we successfully detected 2 miRNAs (miR-505-3p and miR- 21a-5p) and an internal control (miR-16-5p) with only one reaction based on competitive PCR (cPCR) with high sensitivity. For each miRNA, two stem-loop reverse transcription (RT) primers were designed to produce two different templates: the competitor cDNA and the target cDNA, which had similar sequences except for 3 nucleotides different in length. RNA from a control sample was reverse transcribed with the competitive RT primers of multiple genes. Samples for test were reverse transcribed with target RT primers to obtain target cDNAs. Target cDNA was mixed with competitor cDNA to be used as the template for a multiplex fluorescent cPCR reaction. The cPCR products were separated on polyacrylamide gel electrophoresis with ABI 377 DNA sequencer and each fluorescent peak was quantified by its intensity. In this method, we compared the expression level of miR-505-3p in two tissues (thalamus and tail) between C57BL/6J and C3H/HeJ mice. The results showed that in the thalamus, which had high abundance of miR-505-3p, both cPCR and SYBR Green based qRT-PCR provided a sensitive quantification outcome. However, in the tail, which had extremely low level of miR-505-3p, it could be steadily detected by cPCR even after 8 times dilution with a relatively high sensitivity, while qRT-PCR can’t detect any product only after 2 times dilution. The variation as low as 12.2% between samples could be clarified by cPCR, which could not be accomplished by qRT-PCR. This method enables multiplex, accurate and sensitive quantification of miRNAs with fewer precious RNA samples than qRT-PCR.