Characterization of Hot Deformation Behavior and Processing Map of As‑Cast H13 Hot Work Die Steel

Yahui Han,Changsheng Li,Jinyi Ren,Chunlin Qiu,En LI,Shuaishuai Chen 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.9

The hot-working behavior of as-cast H13 hot work die steel was investigated in the method of isothermal compression testinvolving the wide deformation temperatures of 900–1150 °C and strain rates of 0.01–10 s−1, with the true strain to 0.8, onthe MMS-200 thermo-mechanical simulator. Two characteristic parameters involving the critical strain for DRX initiation(c ) and the strain for peak stress (p ) were identified. The ratio of critical strain to peak strain ranged from 0.26 to 0.6, whichdecreased with the increase in temperature and decrease in strain rate. Processing maps were established using dynamicmaterial model at strains of 0.2, 0.4, 0.6, 0.8. The power dissipation maps were not significantly affected by the strain, whilethe instability maps were sensitivity with the strain when it was over 0.4. The area of instability domain at strain of 0.8 wasthe largest. The instable characteristics contained the mixed grain structure, adiabatic shear band, intense deformation inserious deformation area and brittle elemental segregation area. The chief effect on the power dissipation was the strain rate,the optimum hot working parameters at strain of 0.8 (910–985 °C, 1010–1150 °C and 0.01–0.05 s−1) were determined. Inthis filed, the original coarse as-cast grains were gradually refined by dynamic recrystallization mechanism and the DRXgrain numbers had a significant increase with the increase of power dissipation efficiency.

Fault diagnosis method of belt conveyor idler based on sound signal

Yahui Zhang,Siyan Li,Aimin Li,Gaoxiang Zhang,Mingzhuang Wu 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.1

Damage to a belt conveyor idler will increase the downtime and maintenance cost, so it is very important to diagnose its fault. At present, the fault diagnosis of the idler of a belt conveyor is mostly based on vibration and temperature signal. However, contact fault diagnosis approaches are severely limited when sensors are inconvenient to install or when vibration and temperature signals cannot be returned. In this special case, the non-contact fault diagnosis method, represented by measuring acoustic signals, becomes a necessary means. To effectively extract mechanical state information from sound signals of belt conveyors and identify typical mechanical faults, we propose a fault detection method based on sample center distance weighted (support vector data description (SVDD)) and multi-frame fusion (Melfrequency cepstral coefficient (MFCC)) features. Aiming at the disadvantage that single frame MFCC features and traditional SVDD are susceptible to noise, multi-frame fusion MFCC optimization features are used as samples, and the weighted SVDD model based on sample center distance is used for fault detection. Finally, the overall recognition accuracy of the experiment is greatly improved. It is proved that MFCC features of multi-frame fusion sound signal and weighted SVDD fault detection based on sample center distance can effectively determine whether there is a fault in the of belt conveyor idler.

Achieving High Yield of Lactic Acid for Antimicrobial Characterization in Cephalosporin-Resistant Lactobacillus by the Co-Expression of the Phosphofructokinase and Glucokinase

( Yahui Gong ),( Tiyuan Li ),( Shiyu Li ),( Zhenyou Jiang ),( Yan Yang ),( Junli Huang ),( Zhaobing Liu ),( Hanxiao Sun ) 한국미생물 · 생명공학회 2016 Journal of microbiology and biotechnology Vol.26 No.6

Lactobacilli are universally recognized as probiotics that are widely used in the adjuvant treatment of inflammatory diseases, such as vaginitis and enteritis. With the overuse of antibiotics in recent years, the lactobacilli in the human body are killed, which could disrupt the microecological balance in the human body and affect health adversely. In this work, cephalosporin-resistant Lactobacillus casei RL20 was obtained successfully from the feces of healthy volunteers, which possessed a stable genetic set. However, the shortage of lactic acid (72.0 g/l at 48 h) by fermentation did not meet the requirement for its use in medicine. To increase the production of lactic acid, the functional genes pfk and glk were introduced into the wild strain. A yield of 144.2 g/l lactic acid was obtained in the transgenic L. casei RL20-2 after fermentation for 48 h in 1 L of basic fermentation medium with an initial glucose concentration of 100 g/l and increasing antibacterial activity. These data suggested that L. casei RL20-2 that exhibited a high yield of lactic acid may be a potential probiotic to inhibit the spread of bacterial infectious diseases and may be used for vaginitis therapy.

Optimal Control Of Two-Hop Routing In Dtns With Time-Varying Selfish Behavior

( Yahui Wu ),( Su Deng ),( Hongbin Huang ) 한국인터넷정보학회 2012 KSII Transactions on Internet and Information Syst Vol.6 No.9

The transmission opportunities between nodes in Delay Tolerant Network (DTNs) are uncertain, and routing algorithms in DTNs often need nodes serving as relays for others to carry and forward messages. Due to selfishness, nodes may ask the source to pay a certain reward, and the reward may be varying with time. Moreover, the reward that the source obtains from the destination may also be varying with time. For example, the sooner the destination gets the message, the more rewards the source may obtain. The goal of this paper is to explore efficient ways for the source to maximize its total reward in such complex applications when it uses the probabilistic two-hop routing policy. We first propose a theoretical framework, which can be used to evaluate the total reward that the source can obtain. Then based on the model, we prove that the optimal forwarding policy confirms to the threshold form by the Pontryagin`s Maximum Principle. Simulations based on both synthetic and real motion traces show the accuracy of our theoretical framework. Furthermore, we demonstrate that the performance of the optimal forwarding policy with threshold form is better through extensive numerical results, which conforms to the result obtained by the Maximum Principle.

Energy-efficient Joint Control of Epidemic Routing in Delay Tolerant Networks

( Yahui Wu ),( Su Deng ),( Hongbin Huang ) 한국인터넷정보학회 2013 KSII Transactions on Internet and Information Syst Vol.7 No.2

Due to the uncertain of connections in Delay Tolerant Networks (DTNs), most routing algorithms in DTNs need nodes to forward the message to others based on the opportunistic contact. The contact is related with the beaconing rate. In particular, nodes have more chances to encounter with each other with bigger beaconing rate, but more energy will be used. On the other hand, if the nodes forward the message to every node all the time, the efficiency of the routing algorithm is better, but it needs more energy, too. This paper tries to exploit the optimal beaconing rate and forwarding rate when the total energy is constraint. First, a theoretical framework is proposed, which can be used to evaluate the performance with different forwarding rate and beaconing rate. Then, this paper formulates a joint optimization problem based on the framework. Through Pontryagin`s Maximal Principle, this paper obtains the optimal policy and proves that both the optimal forwarding and beaconing rates conform to threshold form. Simulation results show the accuracy of the theoretical framework. Extensive numerical results show that the optimal policy obtained in this paper is the best.

QoE-driven Joint Resource Allocation and User-paring in Virtual MIMO SC-FDMA Systems

( Yahui Hu ),( Song Ci ) 한국인터넷정보학회 2015 KSII Transactions on Internet and Information Syst Vol.9 No.10

This paper is concerned with the problem of joint resource allocation and user-pairing in virtual MIMO SC-FDMA systems to improve service quality of experience (QoE). No-reference logarithmic model is introduced to quantify service experience for each user and the objective is to maximize sum of all user`s mean of score (MOS). We firstly formulate the optimal problem into an S-dimensional (S-D) assignment problem. Then, to solve this problem, the modified Lagrangian relaxation algorithm is deduced to obtain the suboptimal result of joint user-paring and subchannel allocation. The merits of this solution are as follows. First, the gap between its results and the global optimal one can be quantified and controlled by balancing the complexity and accuracy, which merit the other suboptimal algorithms do not have. Secondly, it has the polynomial computational complexity and the worst case complexity is O(3LN³), where L is the maximum iteration time and N is the number of subchannels. Simulations also prove that our proposed algorithm can effectively improve quality of experience and the gap between our proposed and the optimal algorithms can be controlled below 8%.

Dynamic intelligent control of composite buildings by using M-TMD and evolutionary algorithm

Yahui Meng,Z.Y. Chen,Ruei-Yuan Wang,Sheng-Hsiang Peng,Yaoke Yang,Timothy Chen 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.5

The article deals with the possibilities of vibration stimulation. Based on the stability analysis, a multi-scale approach with a modified whole-building model is implemented. The motion equation is configured for a controlled bridge with a MDOF (multiple dynamic degrees of freedom) Tuned Mass Damper (M-TMD) system, and a combination of welding, excitation, and control effects is used with its advanced packages and commercial software submodel. Because the design of high-performance and efficient structural systems has been of interest to practical engineers, systematic methods of structural and functional synthesis of control systems must be used in many applications. The smart method can be stabilized by properly controlling the high frequency injection limits. The simulation results illustrate that the multiple modeling method used is consistent with the accuracy and high computational efficiency. The M-TMD system, even with moderate reductions in critical pressure, can significantly suppress overall feedback on an unregulated design.

Effect of Homogenisation Temperature on the Microstructure and Microhardness of As-Cast H13 Steel

Yahui Han,Changsheng Li,Shuai He,Cairu Gao,Shuaishuai Chen,En Li 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.3

This study determined that the homogenisation temperature range of experimental as-cast H13 steel was from 1150 to1230 °C, whilst the effect of homogenisation temperature range on the microstructural evolution and microhardness wastested. The enrichment of alloying elements in the dendrite segregation region decreased the solidus temperature of matrix,whose total content determined the maximum homogenisation temperature. The secondary dendrite branches were mostdissolved at 1150 °C, and overheating appeared at 1230 °C in the segregation region. Moreover, the primary carbidesunderwent shrinking, passivation, fragmentation and dissolution. The secondary carbides M23C6and M6Cwere formed atthe interfaces of MC/γ and M7C3/γ, respectively. As the homogenisation temperature increased from 1150 to 1230 °C, thevalue of microhardness gradually decreased from 771 to 740 HV. Nevertheless, the standard deviation value decreased firstand then increased, which reached the minimum 32 HV at 1200 °C, indicating that the hardness homogeneity was the best.

Photoelectrochemical Properties and Photocatalytic Activity of Fluorine-Doped Plate-Like WO3 from Hydrothermal Radio-Frequency (RF) Sputtered Tungsten Thin Films

Yahui Yang,GuanHua Jin,Hang Li 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.4

Fluorine-doped tungsten oxide (WO3) plate-like films were synthesized by hydrothermal radiofrequency (RF) sputtered tungsten (W) thin films in HF solution. The crystal structure, composition and morphology of nitrogen fluorine (F) doped WO3 were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectra (DRS) techniques. The results indicate that fluorine can be doped successfully into WO3 plate-like films by hydrothermal synthesis in hydrofluoric acid (HF) solution. The F-doped WO3 samples show stronger absorption in the UVVis range and a red shift in the band gap transition. Incident photon to current efficiency (IPCE) measurements carried out on photoelectrochemical cell with F-doped WO3 plate-like films as anodes demonstrate a significant increase of photoresponse in the visible region compared with undoped WO3. The photocatalytic activity under visible light irradiation for newly synthesized F-doped WO3 plate-like films was investigated by degradation of methyl orange. The photocatalytic activity of F-doped WO3 plate-like films was 3-fold enhancement compared with pure WO3 samples.

Secure Message Distribution Scheme with Configurable Privacy in Heterogeneous Wireless Sensor Networks

LI, YaHui,MA, JianFeng,MOON, SangJae The Institute of Electronics, Information and Comm 2010 IEICE transactions on information and systems Vol.93 No.3

<P>Security and privacy of wireless sensor networks are key research issues recently. Most existing researches regarding wireless sensor networks security consider homogenous sensor networks. To achieve better security and performance, we adopt a heterogeneous wireless sensor network (HWSN) model that consists of physically different types of sensor nodes. This paper presents a secure message distribution scheme with configurable privacy for HWSNs, which takes advantage of powerful high-end sensor nodes. The scheme establishes a message distribution topology in an efficient and secure manner. The sensor node only need generate one signature for all the messages for all the users, which can greatly save the communication and computation cost of the sensor node. On the other hand, the user can only know the messages that let him know based on a pre-set policy, which can meet the requirement of the privacy. We show that the scheme has small bandwidth requirements and it is resilient against the node compromise attack.</P>