The Faceted Discrete Growth and Phase Differentiation During the Directional Solidification of 20SiMnMo5 Steel

Xiaoping Ma,Dianzhong Li 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.4

The microstructures, segregation and cooling curve were investigated in the directional Solidification of 20SiMnMo5 steel. The typical characteristic of faceted growth is identifi ed. The microstructures within the single cellular and within the singledendritic arm, together with the contradictive segregation distribution against the cooling curve, verify the discrete crystalgrowth in multi-scales. Not only the single cellular/dendritic arm but also the single martensite zone within the single cellular/dendritic arm is produced by the discrete growth. In the viewpoint of segregation, the basic domain following continuousgrowth has not been revealed. Along with the multi-scale faceted discrete growth, the phase Differentiation happens forboth the solid and liquid. The Differentiated liquid phases appear and evolve with Different sizes, positions, compositionsand durations. The physical mechanism for the faceted discrete growth is qualitatively established based on the nucleationof new faceted steps induced by the composition gradient and temperature gradient.

Congestion Control for Internet of Things Based on Priority

Lujuan Ma,Huanqing Wang,Yucheng Zhou,Xiaoping Deng,Xiaoping Liu 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.4

5th generation mobile networks (5G) provides better support for Internet of Things (IoT). However, heavy IoT traffic flowing into the Internet causes network congestion, which significantly degrades network performance and quality of service (QoS). In this paper, the congestion problem in IoT is formulated as a control problem. And then adaptive backstepping is applied to resolve the congestion control problem and a new congestion control mechanism called Congestion Control Based on Priority (CCBP) is proposed. CCBP is aware of the packet loss ratios in the access network by estimation. Besides, priority parameters can be adjusted according to the priority of different applications to achieve different congestion control in CCBP. Simulation results clarify that the convergence time of CCBP is 5% of BARED and the packet loss ratio of CCBP is 4 orders of magnitude lower than BARED. And the throughput of CCBP is 4 times that of BARED. Different throughputs and queue packet loss ratios are achieved by adjusting parameters. Besides, when network parameters such as RTT and packet loss ratio in access network change, CCBP also has satisfactory performance.

Microwave-Assisted Hydrothermal Preparation of SnO2/MoS2 Composites and Their Electrochemical Performance

Lin Ma,Xiaoping Zhou,Limei Xu,Xuyao Xu,Lingling Zhang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.2

We introduce a two-step hydrothermal and microwave method to prepare novel SnO2/MoS2 composites. The as-prepared samples are well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The experimental results indicate that the SnO2/MoS2 composites are composed of MoS2 nanosheets and ultrafine SnO2 nanoparticles with mean size of 3–4 nm which are well-distributed and anchored on the surface of MoS2 nanosheets. The resultant composites demonstrate prominently improved electrochemical performances, which could be attributed to the unique and robust microstructures and synergetic effect between MoS2 and SnO2.

Urinary Hypoxia-Inducible Factor-1alpha Levels Are Associated with Histologic Chronicity Changes and Renal Function in Patients with Lupus Nephritis

Chunyang Ma,Zhuori Li,Jiali Wei,Feng Zhan,Ru Wang,Keying Fu,Xiaoping Wan 연세대학교의과대학 2012 Yonsei medical journal Vol.53 No.3

Purpose: Tubulointerstitial hypoxia in the kidney is considered a hallmark of injury and a mediator of the progression of tubulointerstitial fibrosis. Hypoxia-inducible factor-1alpha (HIF-1alpha), a master transcription factor in cellular adaptation to hypoxia,regulates a wide variety of genes, some of which are closely associated with tissue fibrosis. The present study set out to characterize urinary HIF-1alpha expressions in patients with lupus nephritis (LN) and to explore whether urinary HIF-1alpha expressions are associated with histologic chronicity changes and renal function. Materials and Methods: Urinary HIF-1alpha levels were measured by enzyme-linked immunosorbent assays in 42 patients with LN and in 30 healthy controls. Activity and chronicity indexes as well as tubular HIF-1alpha expressions were analyzed for each specimen. Results: Urinary HIF-1alpha levels were higher in LN patients than in healthy controls (3.977±1.696 vs. 2.153±0.554 ng/mL, p<0.001) and were associated with histologic chronicity indexes (r=0.463, p<0.01) and eGFR (r=-0.324, p<0.05). However, urinary HIF-1alpha levels showed no correlation with histologic activity indexes, anti-dsDNA, ANA, complement 3 and 4 levels, proteinuria, systemic lupus erythematosis disease activity index, and WHO pathological classification (p>0.05). Conclusion: Urinary HIF-1alpha levels were elevated in LN patients and were associated with histologic chronicity changes and renal function, indicating that HIF-1alpha might contribute to histologic chronicity in LN.

Congestion Tracking Control for Wireless TCP/AQM Network Based on Adaptive Integral Backstepping

Lujuan Ma,Xiaoping Liu,Huanqing Wang,Yucheng Zhou 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.9

This paper extends the backstepping control strategy to wireless Transmission Control Protocol (TCP) network to solve the Active Queue Management (AQM) problem. Different from the wired network, the uplink and downlink of the wireless network are asymmetric and the packet loss may be caused by congestion and may occurs during the transmission over wireless links. Inspired by the existing backstepping design idea for a wired network model, an adaptive tracking controller is proposed to deal with the congestion problem in wireless network. The uplink and downlink packet losses are estimated by adaptive update laws. The presented method provides satisfactory tracking performance in the network. Meanwhile, the packet loss is small. The simulation results show the feasibility of the proposed method.

Sensitivity of Tropical Cyclone Intensity and Structure to Vertical Resolution in WRF

Zhanhong Ma,Jianfang Fei,Xiaogang Huang,Xiaoping Cheng 한국기상학회 2012 Asia-Pacific Journal of Atmospheric Sciences Vol.48 No.1

In this paper the impacts of vertical resolution on the simulations of Typhoon Talim (2005) are examined using the Weather Research and Forecasting (WRF) model, with cumulus parameterization scheme representing the cumulus convection implicitly. It is shown that the tropical cyclone (TC) track has little sensitivity to vertical resolution, whereas the TC intensity and structure are highly sensitive to vertical resolution. It is partly determined by the sensitivity of the planetary boundary layer (and the surface layer) and the cumulus convection processes to vertical resolution. Increasing vertical resolution in the lower layer could strengthen the TC effectively. Increasing vertical resolution in the upper layer is also beneficial for the storm intensification, but to a lesser degree. In contrast, improving the midlevel resolution may cause the convergence of environmental air,which inhibits the TC intensification. The results also show that the impacts of vertical resolution on features of the TC structure, such as the tangential winds, secondary circulations and the evolution of the warm-core structure, are consistent with the impacts on the TC intensity. It is suggested that in the simulations of TCs, the vertical levels should be distributed properly rather than the more the better,with higher vertical resolution being expected both in the lower and upper layer, while the middle layer should not hold too many levels.

One-Pot Hydrothermal Synthesis of Sulfur-Doped SnO2 Nanoparticles and their Enhanced Photocatalytic Properties

Lin Ma,Limei Xu,Xuyao Xu,Xiaoping Zhou,Lingling Zhang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.3

Sulfur-doped SnO2 nanoparticles with ultrafine sizes have been successfully prepared by a one-pot hydrothermal method. The obtained samples are characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), thermogravimetric (TG), analyzer UV-Vis spectroscopy, photoluminescence (PL) and electrochemical impedance spectroscopy (EIS). The experimental results indicate that the doping level of sulfur element as well as the bandgaps of SnO2 can be controlled to a certain extent by varying the amount of L-cysteine (L-cys). When evaluated as photocatalysts in the degradation of rhodamine B (RhB) and reduction of Cr(VI) under visible light region, the resultant sulfur-doped SnO2 nanoparticles demonstrate obviously enhanced photocatalytic activities due to the markedly improved visible light response and effective separation of the photo-generated electron–hole pairs.

Numerical Simulation of Tensile Behavior of 3D Orthogonal Woven Composites

Xiaori Yang,Xiaoping Gao,Yayun Ma 한국섬유공학회 2018 Fibers and polymers Vol.19 No.3

In this paper, the composite reinforced with three dimensional orthogonal woven fabric/epoxy resin was fabricated with vacuum assisted resin transfer model. The tensile behavior in 0 o and 90 o directions were experimentally executed. The tensile behavior of 3D orthogonal woven composite was numerical simulated based on the unit cell model and compared with the experimental result, the influence of crack damage and stress on fiber, resin and fiber/resin interface was analyzed. The maximum differences between experimental and simulated results are 3.23 % and 7.94 %. The verified model can be used to simulate the other static and dynamic mechanical properties and analyze the influence of the behavior of component material on the mechanical material properties of 3DOWC.

Investigation on characteristics of pressure fluctuation in a centrifugal pump with clearance flow

Lulu Zheng,Xiaoping Chen,Wei Zhang,Zu-chao Zhu,Jinglei Qu,Mengmeng Wang,Xiaojie Ma,Xueli Cheng 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.9

Clearance flow has great impact on pressure fluctuation of centrifugal pumps. Numerical calculations are performed to study the pressure fluctuation characteristics of centrifugal pump with wear ring clearance, especially in the regions of interaction between main flow and clearance flow (IMC) and clearance. The accuracy of numerical calculations is illustrated by comparing the experiments of performance and pressure fluctuation. Results show that, in clearance region the pressure fluctuation is still governed by blade passing frequency (f BPF ). Its amplitude of dominate frequency of pressure fluctuation becomes larger as the probe approaches the impeller exit. In IMC region, the pressure fluctuation at impeller outlet is dominated by f BPF . However, the dominate frequency at the entrance of impeller is less than f BPF . In addition, as the flow rate increased, the amplitude of dominate frequency of pressure fluctuation increases at impeller entrance, whereas an inverse trend is observed at wear ring clearance region.

Joint Beamforming for Secure Communication in RIS-Assisted Cognitive Radio Networks

Xuewen Wu,Jingxiao Ma,Xiaoping Xue 한국통신학회 2022 Journal of communications and networks Vol.24 No.5

This paper studies the security and communication efficiency problem of a reconfigurable intelligent surface (RIS) assisted cognitive radio network, in which we proposed a scheme where secrecy rate (SR) and transmission rate are jointly considered. In specific, with the help of RIS, we exploit the green interference caused by the secondary network to ensure the physical layer security of the primary network. By taking the mutual interference between these two networks into account, we establish a problem to minimize the total transmit power subject to the quality-of-service requirement of secondary user (SU), SR requirement of the primary users (PUs) and limited interference temperature of PUs. In our proposed iterative algorithm, the transmit and reflect beamforming are alternatively optimized by transforming PUs’ SR constraint into a second order cone (SOC) form, and the optimal transmit and reflect beamforming are achieved based on the iterative penalty function. Simulation results show the superiority of our proposed algorithm in terms of the total transmit power requirement compared with other benchmarks, and the total transmit power of our proposed algorithm is not very susceptible to the number of eavesdroppers and PUs, which is conducive to serving multiple users in the wireless communication system.