Observation of temperature-dependent kinetics for catalytic CO oxidation over TiO₂-supported Pt catalysts

Yu, Xiaomei,Wang, Yunfei,Kim, Ansoon,Kim, Yu Kwon Elsevier 2017 Chemical physics letters Vol.685 No.-

<P>TiO2-supported Pt catalysts were prepared for the study of CO oxidation kinetics at reaction conditions of pressures (1-100 Torr) and temperatures (300-500 K). We find two distinct temperature ranges with different reaction kinetics distinguished by an abrupt slope change at around 380 K in the Arrhenius plot only with the excess O-2, not with the stoichiometric O-2/CO ratio. We propose that Pt oxides are formed during the catalytic reactions with increasing temperatures under the oxidizing condition and the origin of the slope change is due to the changes in the reaction pathways of CO oxidation due to the Pt oxide formation. (C) 2017 Elsevier B.V. All rights reserved.</P>

Impressive Photocatalytic Performance of 2D Orthorhombic SnS/FTO Thin Layers in Photoelectrocatalytic Hydrogen Production

Xiaomei Yu,Yunfei Wang,Malkeshkumar Patel,Joondong Kim,Yu Kwon Kim 한국에너지기후변화학회 2017 한국에너지기후변화학회 학술대회 Vol.2017 No.5

Electrical and Mechanical Properties of Epoxy Composites Reinforced with Kaolin-Coated Basalt Fibers

He-Chen Liu,Yu Sun,Mingjia Zhang,Yun-Peng Liu,Yunfei Yu,Hong Yu 한국섬유공학회 2023 Fibers and polymers Vol.24 No.1

Basalt fiber (BF) is appropriately used for manufacturing insulating rods because of its excellent aging resistance, hightemperature resistance, electrical insulation, and mechanical strength. However, due to the inert structure on the surface ofthe fiber, the close bonding between the fiber and the resin is hindered. The low bonding strength of the fiber/resin interfacewill significantly reduce the mechanical and insulation properties of the composite, which limits its application in electricalequipment such as insulating rods and insulators. Therefore, this paper attempts to improve the surface roughness of BF byusing Kaolin to strengthen the bonding strength between BF and matrix resin, and analyze and study the mechanical and insulationproperties of the composites before and after modification. The Kaolin content coated on BF ranged from 0.5 to 2 wt%,and the composites modified by 1.5wt%Kaolin (1.5-wt%-K-BFRP) exhibited excellent electrical insulation and mechanicalperformance. Compared with untreated BFRP, the electrical breakdown strength and flashover voltage of 1.5-wt%-K-BFRPincreased by 18.49% and 10.69%, elevated to the 20.57 kV/mm and 13.04 kV, respectively, and the dielectric loss decreasedby 49%, down to 0.83%. The above results indicate that modified BFRP has excellent insulation strength and is suitable forthe manufacture of insulating devices. Furthermore, the bending strength, bending modulus, tensile strength, and interlayershear strength of 1.5-wt%-K-BFRP increased by 67.59%, 21%, 14.56%, and 103.7%, respectively, compared with untreatedBFRP, reach to 465.17 MPa, 31.49 GPa, 562.3 MPa, 26.44 MPa.

g-C₃N₄/TiO₂ nanotubes composite materials for photocatalytic H₂ evolution under visible light irradiation

Yunfei Wang,Yoo Kwan Kim,Yu Kwon Kim 한국에너지기후변화학회 2017 한국에너지기후변화학회 학술대회 Vol.2017 No.11

Sensitivity Analysis of Laser Quenching Parameters of ASTM 1045 of Disk Laser Based on Response Surface Method

Zhibin Yu,Chang Li,Zhengwei Chen,Yunfei Li,Xing Han 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

Laser hardening is an important branch of laser surface hardening technology, which is widely used in metallurgy, transportation,machinery manufacturing, aerospace and other fields. At present, relying entirely on experience or process trial-anderrormethod, it can not effectively reveal the transient mechanism of laser quenching of disk laser, which is not conduciveto shortening the research and development cycle and saving costs. The numerical simulation provides an effective way toobtain the dynamic evolution law of multi-field coupling in laser quenching process. In this paper, a thermo-mechanicalcoupling model of ASTM 1045 laser quenching process by disk laser is established. In the model, the temperature-dependentphysical parameters were calculated by CALPHAD method. The transient law of temperature and microstructural transformationduring quenching was obtained by solving the model. The formation and transformation degree of martensite werecharacterized by the dynamic changes of the depth and width of quenched transformation layer. The quenching structure andtransformation hardening law were observed by Axioskop 2 SEM and Zeiss-IGMA HD FE-SEM to verify the accuracy ofthe simulation results. On this basis, the process parameters of laser quenching were sampled by Monte-Carlo method basedon response surface methodology. The sensitivity effects of different process parameters on the temperature field and phasechange field of laser quenching were analyzed, which laid a theoretical foundation for the optimization of process parameters.

The role of active species in the N₂ and N₂-H₂ RF afterglows on selective surface nitriding of ALD-grown TiO₂ films

Wang, Yunfei,Ricard, Andre,Sarrette, Jean-Philippe,Kim, Ansoon,Kim, Yu Kwon Elsevier Sequoia 2017 Surface & coatings technology Vol.324 No.-

<P><B>Abstract</B></P> <P>We find that surface modification characteristics of TiO<SUB>2</SUB> using N<SUB>2</SUB> RF plasma are strongly dependent on the detailed composition of active species in the plasma and the afterglows. The surface nitriding of ALD-grown TiO<SUB>2</SUB> films in pure N<SUB>2</SUB> RF afterglows at room temperature (RT) is found to be more effective in the late afterglows than in the early afterglows. Adding a small fraction of H<SUB>2</SUB> in N<SUB>2</SUB> results in suppression of surface nitriding, suggesting that the change in the composition of the active species in the afterglows by H<SUB>2</SUB> is the origin to the suppressed nitriding performance. Here, we present our analysis on the surface chemical composition after the plasma modification as well as the densities of excited species such as N atoms, N<SUB>2</SUB>(A) and N<SUB>2</SUB>(X, <I>v</I>) metastable molecules and N<SUB>2</SUB> <SUP>+</SUP> ions in the afterglows of RF N<SUB>2</SUB> and N<SUB>2</SUB>–H<SUB>2</SUB> (<5%) at different positions along the downstream by emission spectroscopy. The early afterglow of N<SUB>2</SUB> changes from a pink to a late afterglow where the N+N recombination is the dominant process with the introduction of H<SUB>2</SUB>. The roles of active species such as N–atoms and N<SUB>2</SUB> <SUP>+</SUP> ions on TiO<SUB>2</SUB> surface nitriding are found to oppose to each other. We find that N atoms enhance the surface nitriding, while N<SUB>2</SUB> <SUP>+</SUP> ions are likely to deplete the surface-bound N species.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Surface nitriding of TiO<SUB>2</SUB> in the N<SUB>2</SUB> RF afterglow at RT is strongly dependent on the active species densities. </LI> <LI> High density of neutral N atoms plays a beneficial role in the surface nitriding of TiO<SUB>2</SUB>. </LI> <LI> The vibrationally excited N<SUB>2</SUB> and N<SUB>2</SUB> <SUP>+</SUP> species play a negative role in the surface nitriding performance. </LI> </UL> </P>

Visual Attention Servo Control for Task-specific Robotic Applications

Dong Liu,Ming Cong,Yu Du,Yunfei Zhang,Clarence W. de Silva 제어·로봇·시스템학회 2013 International Journal of Control, Automation, and Vol.11 No.6

This paper proposes a visual attention servo control (VASC) method which uses the Gaussian mixture model (GMM) for task-specific applications of mobile robots. In particular, low dimensional bias feature template is obtained using GMM to get an efficient attention process. An image-based visual servo (IBVS) controller is used to search for a desired object in a scene through an attention system which forms a task-specific state representation of the environment. First, task definition and object representation in semantic memory (SM) are proposed, and bias feature template is obtained using GMM deduction for features from high dimension to low dimension. Second, the features intensity, color, size and orientation are extracted to build the feature set. Mean shift method is used to segment the visual scene into discrete proto-objects. Given a task-specific object, top-down bias attention is evaluated to generate the saliency map by combining with the bottom-up saliency-based attention. Third, a visual attention servo controller is developed to integrate the IBVS controller and the attention system for robotic cognitive control. A rule-based arbitrator is proposed to switch between the episodic memory (EM)-based controller and the IBVS controller depending on whether the robot obtains the desired attention point on the image. Finally, the proposed method is evaluated on task-specific object detection under different conditions and visual attention servo tasks. The obtained results validate the applicability and usefulness of the developed method for robotics.

Real-time detection of the nanoparticle induced phytotoxicity in rice root tip through the visible red emissions of Eu³⁺ ions

Du, Peng,Wu, Yunfei,Yu, Jae Su The Royal Society of Chemistry 2018 PHOTOCHEMICAL AND PHOTOBIOLOGICAL SCIENCES Vol.17 No.4

<P>Phytotoxicity is one of the most important factors involved in the reduction of crop production. With the introduction of NaBiF4 nanoparticles, the effect of the particle size (>50 nm) on rice development was systematically studied. Through the exogenous treatment of multiple concentrations of nanoparticles, the primary root length, lateral root number, and lateral root length were significantly inhibited under higher content of nanoparticles, but more crown root formation was induced, which might be due to phytotoxicity. With the help of the red emission of the Eu<SUP>3+</SUP>-activated NaBiF4 nanoparticles, we could infer that the nanoparticles were accumulated in the root tip cells in the division and elongation zone but not in the mature region. Additionally, the investigation on the influence of the studied nanoparticles on the gene level and the expression of phytotoxicity related genes was performed to further identify the effect of the nanoparticles on the rice root development. These results potentially explain the effect of larger nanoparticles on phytotoxicity in the plant roots.</P>

Study of Proteolysis, Lipolysis, and Volatile Compounds of a Camembert-type Cheese Manufactured Using a Freeze-dried Tibetan Kefir Co-culture during Ripening

Jun Mei,Qizhen Guo,Yan Wu,Yunfei Li,Huaning Yu 한국식품과학회 2015 Food Science and Biotechnology Vol.24 No.2

The use of a freeze-dried Tibetan kefir coculture as a starter for production of Camembert-type cheese was investigated. Maturation of produced cheese was monitored for 35 days and the chemical composition, proteolysis, lipolysis, and volatile compounds were studied. The cheese underwent proteolysis. The content of pH 4.6- soluble nitrogen, 12% trichloroacetic acid-soluble nitrogen, and the total free amino acid content increased while the total nitrogen content decreased. Palmitic, myristic, oleic, and capric acid were the representative free fatty acids, which increased in amount during ripening. A total of 45 compounds were detected, including 16 acids, 8 ketones, 6 alcohols, 7 esters, and 8 unclassified compounds. Volatile carboxylic acids were abundant in the headspace of the cheese.

Formation of Protein Bodies and the Response to Nitrogen in Different Positions During Wheat Endosperm Development

Yang Yang,Xinyu Chen,Liping Ran,Yunfei Wu,Xurun Yu,Zhaodi Dong,Fei Xiong 한국식물학회 2019 Journal of Plant Biology Vol.62 No.4

The development of protein bodies (PBs) determinesthe processing properties of wheat (Triticum aestivum L.). Ithas been known that nitrogen uptake has a strong impact ongrain protein concentration. However, the differences of theformation of PB in different developmental stages anddifferent positions in wheat endosperm are still controversial. To solve these issues, PBs formation in different wheatendosperm parts and the response to nitrogen were investigatedusing light, transmission electron microscopes in presentstudy. The main results were as follows. (1) Proteins mainlyformed PBs via the Golgi apparatus in the vacuole at theearly stage of wheat endosperm development. After 7 dayspost anthesis, most proteins were derived from the roughendoplasmic reticulum. (2) The morphology of PBs was diverseamong different endosperm parts. Compared with the centralendosperm, the PBs in sub-aleurone cells were abundant andlarge. (3) More abundant endoplasmic reticulum, Golgi andmitochondrion were observed at the early stage after nitrogentreatment. Nitrogen also increased the accumulation of PBsat the later stage. (4) The sub-aleurone region cells of theendosperm presented more significant responses to nitrogenthan the central endosperm.