Mathematical modeling of torque for single screw expanders

Yuting Wu,Ruiping Zhi,Wei Wang,Lili Shen,Yeqiang Zhang,Biao Lei,Jingfu Wang,Chongfang Ma 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.1

This paper presents a mathematical model of torque for Single screw expanders (SSEs). Instantaneous torque and torque ratio were analyzed and discussed. The periodic variation of instantaneous torque is the same for different inlet pressure levels. The torque ratio, with its value close to 1, is independent of the inlet pressure of SSE. An experimental system was established to measure the torque, power and shaft efficiency of the self-developed SSE prototype, and results were used to validate the model. Comparison shows that the difference between calculated and experimental torque values is small (6.58 N.m to 7.55 N.m). The calculated and experimental output power is similar, with a difference of 2.07 kW to 2.37 kW. Therefore, the proposed model can be used to estimate the torque and output power of SSEs.

Microstructure and electrical properties of La_2O_3-doped Bi_0.5(Na_0.68K_0.22Li_0.1)_0.5TiO_3 lead-free piezoelectric ceramics

Hong Pan,Yuting Hou,Xiaolian Chao,Lingling Wei,Zupei Yang 한국물리학회 2011 Current Applied Physics Vol.11 No.3

La_2O_3-doped Bi_0.5(Na_0.68K_0.22Li_0.1)_0.5TiO_3 lead-free piezoelectric ceramics have been successfully prepared by conventional solid state method and the effects of La_2O_3 doping on microstructure and electrical properties of the ceramics were investigated. The X-ray diffraction patterns demonstrated all ceramics possessed pure perovskite structure with rhombohedral symmetry. The temperature dependence of dielectric constant and dielectric loss revealed two abnormal dielectric peaks of T_d and T_m,which implied that from room temperature to 500 ℃ all ceramics underwent two phase transitions which were from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric, respectively. It was also found that the transition temperature T_d decreased with the addition of La_2O_3. Diffuse phase transition and frequency dispersion of the dielectric constant were observed in all ceramics. Dielectric relaxor behavior obeyed the modified Curie―Weiss law. The results revealed that all samples had relaxor characteristics. In addition, for the ceramics with 0.1 wt.% La_2O_3, optimized electrical properties were obtained, which were as follows: ε_r = 1254 (1 kHz), tan δ = 0.0483, d_33 = 192 pC/N, K_p = 0.27,P_r = 29.1 μC/cm^2, and E_c = 29.0 kV/cm.

Study on Calculation Model for Compressive Strength of Water Saturated Recycled Aggregate Concrete

Pei Ge,Wei Huang,Hao Zhang,Wenli Quan,Yuting Guo 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.1

It has been proved that the compressive strength of water saturated concrete is lower than that of air dry concrete. Due to the water absorption of recycled aggregate (RA) is noticeably higher than that of natural aggregate (NA), the mechanical properties of water saturated recycled aggregate concrete (RAC) are quite different from those of water saturated natural aggregate concrete (NAC). At the same time, the calculation of concrete compressive strength is the first step of concrete mix proportion design. Therefore, it is essential to investigate the compressive strength of RAC in water saturated state. In this study, firstly, the water content and effective water absorption of NA, recycled brick aggregate (RBA) and recycled concrete aggregate (RCA), as well as the water content and effective water absorption of concrete specimen were tested; secondly, the effects of water/cement ratio, water saturation and coarse aggregate types on the compressive strength of water saturated concrete were studied; finally, the calculation model for compressive strength of water saturated concrete was proposed. The test results show that: Within 120 hours, the maximum effective water absorption of NA, RCA and RBA is 0.32%, 0.61% and 8.18%, respectively. Within 240 hour, the maximum effective water absorption of NAC, recycled concrete aggregate concrete (RCAC) and recycled brick aggregate concrete (RBAC) is 0.73%, 0.81% and 1.89%, respectively. In air dry and water saturated state, the descending order of compressive strength of concrete is: NAC > RCAC > RBAC. The average relative error of the calculation model for compressive strength of water saturated concrete is 7.1%. In the calculation model, water/cement ratio, effective water absorption, water saturation and coarse aggregate types are considered. The results of this study have great significance for the mix proportion design of water saturated concrete.

Study on the internal irreversible losses and process exponent of single screw expanders

Lili Shen,Yuting Wu,Wei Wang,Biao Lei,Wei Duan,Ruiping Zhi 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.3

The irreversible losses including intake pressure, leakage, heat transfer, friction and over-expansion losses have great influence on the expander performance. In this paper, a thermodynamic model is presented to predict the real expansion process exponent and analyze the under-expansion or over-expansion under designed and off-designed operation conditions. The model verified by experimental results has a good agreement. Results showed that the real expansion process exponent of air is higher than the ideal adiabatic index of 1.4 and decreases from 1.716 to 1.644 with the internal volume ratio changing from 1.8 to 6.5. The real expansion process exponent of R123 is close to 1.00 under different internal volume ratio. Compared to the intake pressure, the variation of back pressure has greater influence on the large internal volume ratio than the small one. Thus, to adjust the back pressure is more effective to match the designed condition for the expander with a large internal volume ratio.

Novel design method for constrained conjugate contact curves of line gears based on rolling-up of pitch pattern

Jiang Ding,Yuting Wei,Liwei Liu,Ting Geng 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.9

The line gear is an innovative gear transmission usually manufactured for mini gear boxes in small machines, which is designed according to the meshing theory of threedimensional conjugate contact curves. In a line gear pair, the rotation of driving and driven contact curves will form a couple of virtual revolving bodies, which are defined as pitch patterns. The shapes of pitch patterns indicate the working space of the line gear pair, and different kinds of driving and driven contact curves will commonly lead to diverse pitch patterns. In this paper, the shapes of the pitch patterns are as given constraints to design the line gears applied in confining space. Several types of two-dimensional curves (straight line, sine curve and logarithmic curve) are rolled up to form varying three-dimensional contact curves, which can occupy the same working space accordingly. To further indicate the features of the obtained contact curves, the pressure angles and the strength of line gears are calculated and compared concurrently with an experiment pertaining to their transmission errors. The test results show that the transmission errors of all the line gear pairs are below 3 %, indicating that the design theory proposed in this paper can efficiently deduce contact curves for the line gear in constrained spaces and consequently extend the application of the line gear in industrial use.

Improved design method for line gear pair based on screw theory

Jiang Ding,Liwei Liu,Yuting Wei,Aiping Deng 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.4

The line gear (LG) is a novel gear mechanism based on conjugate space curve meshing theory. It is suitable for micro-mechanical systems due to its small size, light weight, and large transmission ratio. Since its invention, the LG pair has been studied from the perspective of differential geometry. To simplify the design process of the LG pair, we studied the LG pair from the innovative perspective of screw algebra. A unified screw coordinate was created for the LG pair, and velocity screws were established to derive its meshing equations. Moreover, the design equations of the center curves and contact curves were calculated for the driving line teeth and the driven line teeth, respectively. Finally, examples of LG pairs were fabricated for the kinematic performance tests, which indicated that the LG pairs designed according to screw theory were capable of performing a stable transmission.

Well-dispersed graphene toward robust lubrication via reorganization of sliding interface

Zhuang Zhao,Xiaoqiang Fan,Yuting Li,Zihan Zeng,Xiaofeng Wei,Kaiyue Lin,Minhao Zhu 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.119 No.-

Excellent lubrication performance of graphene lubricant is mostly attributed to the dispersion of graphene and forming of tribo-film. Herein, diethylene glycol dodecyl ether (E2C12) functionalized graphene oxide (E2C12-GO) was successfully prepared by simple esterification. The physicochemical properties of as-prepared samples were characterized by a series of characterization methods. E2C12-GO with flat edge and high-level spacing possesses high dispersion stability in PAO 20 base oil. Compared with base oil, 0.08 wt% E2C12-GO could achieve the reduction of average friction coefficient and wear rate by 30 % and 57 % at 150 N, respectively. Even with each long-term friction, E2C12-GO could still maintain the state of robust low friction coefficient. Meanwhile, the addition of E2C12-GO can significantly improve the loadbearing capacity (PB value and PD value) of base oil. The excellent tribological properties of E2C12-GO were attributed to high dispersion and high layer spacing, as well as the reorganization of sliding interface. Prospectively, the E2C12-GO shows promising potential as a multi-functional oil-based lubricating additive in industrial applications.

Histone Demethylase Expression Enhances Human Somatic Cell Nuclear Transfer Efficiency and Promotes Derivation of Pluripotent Stem Cells

Chung, Young Gie,Matoba, Shogo,Liu, Yuting,Eum, Jin Hee,Lu, Falong,Jiang, Wei,Lee, Jeoung Eun,Sepilian, Vicken,Cha, Kwang Yul,Lee, Dong Ryul,Zhang, Yi Elsevier 2015 Cell stem cell Vol.17 No.6

<P><B>Summary</B></P> <P>The extremely low efficiency of human embryonic stem cell (hESC) derivation using somatic cell nuclear transfer (SCNT) limits its potential application. Blastocyst formation from human SCNT embryos occurs at a low rate and with only some oocyte donors. We previously showed in mice that reduction of histone H3 lysine 9 trimethylation (H3K9me3) through ectopic expression of the H3K9me3 demethylase Kdm4d greatly improves SCNT embryo development. Here we show that overexpression of a related H3K9me3 demethylase KDM4A improves human SCNT, and that, as in mice, H3K9me3 in the human somatic cell genome is an SCNT reprogramming barrier. Overexpression of KDM4A significantly improves the blastocyst formation rate in human SCNT embryos by facilitating transcriptional reprogramming, allowing efficient derivation of SCNT-derived ESCs using adult Age-related Macular Degeneration (AMD) patient somatic nuclei donors. This conserved mechanistic insight has potential applications for improving SCNT in a variety of contexts, including regenerative medicine.</P> <P><B>Highlights</B></P> <P> <UL> <LI> H3K9me3 is a barrier for human SCNT reprogramming as in mouse </LI> <LI> Injection of human KDM4A mRNA improves SCNT success in mouse oocytes </LI> <LI> KDM4A also improves human SCNT blastocyst formation and NT-ESC derivation </LI> <LI> H3K9me3 removal facilitates zygotic genome activation in human SCNT embryos </LI> </UL> </P> <P><B>Graphical Abstract</B></P> <P>[DISPLAY OMISSION]</P>

Status and Policies of ICT Integration in Higher Education in Southeast Asian Countries

고장완(Ko, Jang Wan),위옥정(Wei, Yuting),김은진(Kim, Eun Jin) 한국비교교육학회 2020 比較敎育硏究 Vol.30 No.5

[연구목적] 본 연구는 최근 주목을 받고 있는 동남아시아 국가들의 고등교육에서의 ICT 활용과 정책을 살펴보고 관련 쟁점과 도전과제들을 분석하여 고등교육에서의 효과적 ICT 활용 방안을 모색하고자 하였다. 본 연구에서는 특히 아세안 국가이면서 정부차원에서 대학에서의 ICT 활용 시스템 구축에 많은 노력을 기울여 온 말레이시아와 필리핀, 그리고 전반적인 ICT 인프라는 다른 국가들에 비해 상대적으로 부족하지만 최근에 적극적인 노력을 하고 있는 인도네시아를 중심으로 분석하였다. [연구방법] 본 연구는 문헌연구를 중심으로 하였으며, 특히 다양한 정부 보고서 및 발전계획, 정부의 관련 규정, 고등교육기관에서 추진사항을 보고한 대학 보고서, 그리고 관련 컨퍼런스에서 발표한 자료 등을 분석하였다. [연구결과] 본 연구 결과, 연구대상인 말레이시아와 인도네시아, 그리고 필리핀은 고등교육에서의 ICT 활용에 있어서 공통적으로 MOOC를 강조하고 있으며 이러한 특징은 최근의 새로운 경향을 반영한 것으로 보인다. 충분하지 못한 MOOC 인프라와 상대적으로 낮은 수준의 디지털 문해력, 교수와 학생들의 ICT 관련 역량 부족은 세 국가가 공통적으로 겪고 있는 문제점으로 나타났다. [결론] 결론적으로 말레이시아와 인도네시아, 그리고 필리핀은 국가차원에서 ICT 시스템 구축 및 활용에 대한 정부 차원의 노력과 관련 정책을 추진하여 왔으며, 세 국가의 이러한 노력은 앞으로도 지속될 것으로 예상되어 향후 고등교육 발전에 기여할 것으로 보인다. Purposes: The purposes of this study were to examine the current situation of the national policies on ICT for higher education in Southeast Asian countries, especially focusing on Malaysia, Indonesia, and Philippines, to identify the pertinent issues and challenges, and to provide insights for a more effective implementation of ICT into higher education. Methods: Documentary analysis was used in this study. We analyzed official documents including government reports, national strategic plans and government regulations, reports from the HEIs implementing ICT programs, conference proceedings and presentation papers delivered by experts who have been involved in the national initiatives. Results: As a new trend that presents much potential in addressing the various challenges faced by developing countries, MOOC has found its way into all three countries with the involvement of universities in recent years. Insufficient ICT infrastructure, relatively low level of digital literacy and lack of competency and culture in using ICT among instructors and students were identified as some of the common challenges faced by all three countries. Conclusion: The governments in Malaysia, Indonesia and Philippines have shown serious commitment to ICT integration in higher education, and initiated various national educational policies. With the rapid development of new technologies, ICT will continue to have a considerable impact on HEIs in these countries.

Removal of Microcystis aeruginosa and control of algal organic matters by potassium ferrate(VI) pre-oxidation enhanced Fe(II) coagulation

Jihao Zhou,Zhiwei Zhao,Jie Liu,Wei Peng,Xia Peng,Yuting Han,Ping Xiao 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.10

The problem of cyanobacteria blooms during potable water production has generated wide concern. Ferrate( VI) serving as a pre-oxidation tactic was first applied to enhance conventional Fe(II) coagulation for Microcystis aeruginosa-laden water treatment at lab scale. Results demonstrated that ferrate(VI) pre-oxidation could successfully destabilize algae cells through destroying the protective organic layer. The residual ferrate(VI) together with post-added Fe(II) could provoke a comproportionation reaction, where large amounts of Fe hydrolyzates [Fe(OH)3] are formed. The in-situ Fe(OH)3 with abundant reactive surface is responsible for the promotion of flocs growth by facilitating the clustering and cross-linking of algal organic matters (AOM) and cyanobacteria cells, simultaneously resulting in satisfactory reductions in OD680, turbidity and UV254. Overdose of ferrate(VI) could cause severe cell destruction along with the release of intracellular organic matter (IOM), which may impair the water quality by increasing the concentration of dissolved organic carbon (DOC) and the disinfection by-products formation potential (DBPFP). Meanwhile, considering the Fe residual in settled water, the optimal ferrate(VI) dose (20 μM) and Fe(II) dose (80 μM) were proposed. Besides, the synergistic effect of both the degradation by ferrate(VI) and the adsorption by in-situ Fe(OH)3 contributed to the removal of DOC and Microcystin-LR. This study suggests that ferrate(VI) might be a potential candidate for pre-treatment to assist Fe(II) coagulation when addressing algae-laden water.