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A refined design method for precoolers with consideration of multi-parameter variations based on low-dimensional analysis

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Chinese Journal of Aeronautics 2022年第3期35卷 329-344页

作者： Hui LI Zhengping ZOU yumin liu National Key Laboratory of Science and Technology on Aero-Engine Aero-thermodynamics School of Energy&Power Engineering Beihang University Beijing 100083China Advanced Jet Propulsion Creativity Center AEACBeijing 101304China Research Institute of Aero-Engine Beihang University Beijing 100083China International School Beihang University Beijing 100083China

The precooler is a distinctive component of precooled air-breathing engines but constitutes a challenge to conventional thermal design *** latter are based upon assumptions that often reveal to be limited for precooler *** this paper,a refined design method considering the variations of fluid thermophysical properties,flow area and thermal parameters distortion,was proposed to remediate their ***,the precooler was discretized into a fixed number of sub-microtubes based on a new discretization ***,in-house one-dimensional(1D)and two-dimensional(2D)segmented models were established for rapid thermal design and precooler rating with non-uniform airflow,*** heat transfer experimental studies of supercritical hydrocarbon fuel were performed to verify the Jackson correlation for precooler design and the in-house models were validated against the reported data from open *** this basis,the proposed method was employed for the design analysis of hydrocarbon fuel precoolers for precooled-Turbine Based Combined Cycle(TBCC)*** results show that the local performance of precoolers is intrinsically impacted by the aforementioned three *** the case study,the local heat transfer performance is drastically affected by coolant flow *** the circumferential temperature distortion of airflow is weakened by heat *** consideration of additional parameter variations,this novel method improves design accuracy and shortens the design time.

关键词： Compact heat exchangers Heat exchanger design Low-dimensional segmented model Non-uniform inflow Precooled engine Thermophysical properties variation

Dependence of elastic strain field on the self-organized ordering of quantum dot superlattices

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Journal of University of Science and Technology Beijing 2007年第5期14卷 477-481页

作者： yumin liu Zhongyuan Yu Yongzhen Huang School of Science Beijing University of Posts and Telecommunications Beijing 100876 China Key Laboratory of the Ministry of Education of China for Optical Communication and Lightwave Technologies Beijing 100876 China State Key Laboratory on Integrated Optoelectronics Institute of Semiconductors Chinese Academy of Science Beijing 100083 China

A systematic investigation of the strain distribution of self-organized, lens-shaped quantum dot in the case of groffth direction on （001） substrate was presented. The three-dimensional finite element analysis for an array of dots was used for the strain calculation. The dependence of the strain energy density distribution on the thickness of the capping layer was investigated in detail when the elastic characteristics of the matrix material were anisotropic. It is shown that the elastic anisotropic greatly influences the stress, strain, and strain energy density in the quantum dot structures. The anisotropic ratio of the matrix material and the combination with different thicknesses of the capping layer, may lead to different strain energy density minimum locations on the capping layer surface, which can result in various vertical ordering phenomena for the next layer of quantum dots, i.e. partial alignment, random alignment, and complete alignment.

关键词： quantum dot self-organization elastic strain field superlattice

A New Task Scheduling Scheme Based on Genetic Algorithm for Edge Computing

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Computers, Materials & Continua 2022年第4期71卷 843-854页

作者： Zhang Nan Li Wenjing liu Zhu Li Zhi liu yumin Nurun Nahar State Grid Information&Telecommunication Group Co. LtdBeijing102200China University of Chittagong(CU) ChittagongBangladesh

With the continuous evolution of smart grid and global energy interconnection technology,amount of intelligent terminals have been connected to power grid,which can be used for providing resource services as edge *** cloud computing can be used to provide storage services and task computing services in the power grid,but it faces challenges such as resource bottlenecks,time delays,and limited network bandwidth *** computing is an effective supplement for cloud computing,because it can provide users with local computing services with lower ***,because the resources in a single edge node are limited,resource-intensive tasks need to be divided into many subtasks and then assigned to different edge nodes by resource *** task scheduling more efficient is an important *** this paper,a two-layer resource management scheme is proposed based on the concept of edge *** addition,a new task scheduling algorithm named GA-EC(Genetic Algorithm for Edge Computing)is put forth,based on a genetic algorithm,that can dynamically schedule tasks according to different scheduling *** simulation shows that the proposed algorithm has a beneficial effect on energy consumption and load balancing,and reduces time delay.

关键词： Smart grid energy consumption task scheduling resource management

Insight into the degradation mechanism of cefixime under crystallization condition

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Chinese Journal of Chemical Engineering 2018年第7期26卷 1458-1467页

作者： Lingyu Wang Xiaona Li yumin liu DANDan Han Shiyuan liu Teng Zhang Bo Yu Junbo Gong School of Chemical Engineering and Technology Tianjin University

The chemical stability of cefixime was determined by high-performance liquid chromatography （HPLC） under different conditions, including factors such as pH, solvents, initial concentration, temperature and additives. The degradation process follows the first-order kinetics. A pH-rate profile exhibits the U-shape and shows the maximum stability of cefixime at pH = 6. The stability in different pure solvents is ranked as acetone 〉 ethanol 〉 methanol 〉 water, while the degradation rate of cefixime exists a maximum at the ratio of 0.6 in water ＋ methanol mixtures. In addition, the degradation rate increases with the temperature increasing and the activation energy of degradation was found to be 27.078 kJ. mol- 1 in acetone ＋ water mixed solvents. The addition of different additives was proven to either inhibit or accelerate the degradation. The degradation products were analyzed using HPLC, LC-MS and infrared spectroscopy, and the possible degradation pathways in acid as well as alkaline environment were proposed to help us understand the degradation behavior of cefixime.

关键词： Chemical stability Degradation kinetics Degradation Mechanism Cefixime Additives

Breathable,stretchable and adhesive nanofibrous hydrogels as wound dressing materials

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Engineered Regeneration 2021年第1期2卷 63-69页

作者： Xueting liu yumin liu Jingtao Du Xiaoran Li Jianyong Yu Bin Ding State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of TextilesDonghua UniversityShanghai 201620China Innovation Center for Textile Science and Technology Donghua UniversityShanghai 200051China

In spite of the great progress of wound healing materials,the development of dressing with moisture permeabil-ity,stretchable capability,and adhesive performance remains a huge *** this study,gelatin-dopamine(GT-DA)nanofiber membrane was prepared by introducing dopamine(DA)into gelatin(GT)via electrospinning followed by in-situ *** effects of DA dosage,crosslinking condition and crosslinking time on the mechanical properties of the fiber membrane were studied *** resultant GT-DA nanofibrous hydrogels exhibited integrated stress strength of 1.96 MPa,good water absorption of 700%,and water vapor transmission(WVT:4.3 kg m^(-2)d^(-1)),which were superior than those of Mepiform■,a commercial adhesive silicone *** addition,Fe^(3+)were introduced into one side of the nanofiber membrane.A stronger adhesion strength of 2.5 KPa on the porcine skin,which was 1.6 times higher than that of Mepiform■was *** research showed that the prepared nanofibrous hydrogel has potential as wound dressing and could be used in post-traumatic tissue healing *** work presented a type of breathable,stretchable and adhesive nanofibrous hydrogels,which would ensure the stable attachment on wounds during movement as a wound healing material.

关键词： Nanofibrous hydrogels Dopamine Tissue adhesion Stretchable properties Wound dressing materials

Biodegradation of occluded hydrocarbons and kerogen macromolecules of the Permian Lucaogou shales,Junggar Basin,NW China

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Energy Geoscience 2023年第1期4卷 179-184页

作者： Yan'e Chen Longlong Li Zhirong Zhang Paul F.Greenwood yumin liu Wuxi Branch of SINOPEC Petroleum Exploration and Development Research Institute WuxiJiangsu214126China SINOPEC Key Laboratory of Petroleum Accumulation Mechanisms WuxiJiangsu214126China Hubei Key Laboratory of Petroleum Geochemistry and Environment Yangtze UniversityWuhanHubei430100China School of Earth Sciences University of Western AustraliaCrawleyWA6009Australia Western Australia Organic and Isotope Geochemistry Centre School of Earth and Planetary SciencesCurtin UniversityGPO Box U1987PerthWA6845Australia Hubei Key Laboratory of Petroleum Geochemistry and Environment(Yangtze University) Yangtze UniversityWuhan430100China

Three kerogen samples(JJZG-1,JJZG-2 and JJZG-3)isolated from the Permian Lucaogou shales of varying biodegradation levels(BLs≈0,3 and 7,respectively)were subjected to sequential stepwise pyrolysis combined with on-line detection of gas chromatography-mass spectrometry(GC-MS).Occluded fractions(bitumenⅡ)released at low-temperature steps(≥410℃)show consistent biodegradative signatures with that reported for solvent-extracted fractions(bitumenⅠ)of the original shales,e.g.,broad range of abundant n-alkanes,isoprenoids and regular hopanes for the non-biodegraded JJZG-1;trace n-alkanes and abundant hopanes for the moderately biodegraded JJZG-2;and no n-alkanes but still prominent hopanes including the microbially produced 25-nohopanes for the severely biodegraded *** consistency between bitumenⅡand bitumenⅠfractions indicates the biodegradability of the kerogenoccluded bitumenⅡwith limited protection from host kerogen.A minor level of protection was suggested by the trace distribution of n-alkanes in the bitumenⅡof JJZG-2,whereas the bitumenⅠhad no *** kerogen itself was more resistant to biodegradation as reflected by the persistence of high abundances of both n-alkanes and hopanes in the high temperature(≥460℃)products of all three kerogen ***,the relative abundances of these product groups did show some evidence of biodegradation alteration,e.g.,ratios of n-C_(15)alkene/C_(27)hop-17(21)-ene at 510℃pyrolysis decreased by order of magnitude from the non-biodegraded(JJZG-1=27.4)to highly biodegraded(0.3 for JJZG-3)*** reduced biodegradation impact on the kerogen fraction(*** fractions)was also evident by the absence of 25-norhopanes in the high-temperature analysis of the JJZG-3 kerogen.

关键词： Biodegradation Stepwise pyrolysis Occluded hydrocarbon BitumenⅡ Kerogen Source rock Permian Lucaogou shale Junggar Basin

Weak External Bisection of Some Graphs

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Journal of Applied Mathematics and Physics 2024年第1期12卷 91-97页

作者： yumin liu Department of Mathematics Zhejiang Sci-Tech University Hangzhou China Department of Mathematics Lishui University Lishui China

Let G be a graph. A bipartition of G is a bipartition of V (G) with V (G) = V1 ∪ V2 and V1 ∩ V2 = ∅. If a bipartition satisfies ∥V1∣ - ∣V2∥ ≤ 1, we call it a bisection. The research in this paper is mainly based on a conjecture proposed by Bollobás and Scott. The conjecture is that every graph G has a bisection (V1, V2) such that ∀v ∈ V1, at least half minuses one of the neighbors of v are in the V2;∀v ∈ V2, at least half minuses one of the neighbors of v are in the V1. In this paper, we confirm this conjecture for some bipartite graphs, crown graphs and windmill graphs.

关键词： Weak External Bisection Bipartite Graph Windmill Graph

An experiment-library least-squares method on on-line coal element contents analysis

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Science China(Physics,Mechanics & Astronomy) 2012年第11期55卷 2062-2069页

作者： WANG HuiDong LU JingBin LU YuPing YANG Dong MA KeYan YANG Kang liu yumin CHENG DaoWen College of Physics Jilin University Changchun 130012 China Shenzhen National-Power Equipment Ltd. Nanjing 210009 China School of Basic Sciences Changchun University of Technology Changchun 130012 China

A new experiment-library least-squares(experiment-LLs) method used in the neutron inelastic-scattering and thermal-capture analysis(NITA) technique for on-line coal analysis was developed,which has significantly decreased the non-linear radiation *** this method,sixty samples with preset elemental contents were made,from whose experimental spectra twenty single-element spectrum libraries corresponding to twenty kinds of coal were built using the least-squares *** spectrum of the unknown sample was analyzed based on these twenty libraries to estimate its element *** the initial estimated result,the procedure of developing library and analysis was iterated to build a new library with the closest element contents to the unknown *** the experiment-LLs method can reduce non-linear radiation *** experiment-LLs method was performed on an improved coal analysis system which was equipped with a long-life 14 MeV pulsed-neutron generator,a bulk BGO detector with a temperature controller,a moisture meter and coal-smoothing *** precisions of this system for ash content,water content,volatile content and calorific value have reached 1.0wt%,0.5wt%,1.0wt%,350 kJ/kg,respectively.

关键词： on-line coal analysis neutron activation analysis library least-squares

Bulk growth and separation of single-walled carbon nanotubes from rhenium catalyst

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Nano Research 2022年第7期15卷 5775-5780页

作者： Chen Ma yumin liu Lili Zhang liu Qian Yiming Zhao Ying Tian Qianru Wu Dong Li Nan Zhao Xueting Zhang Liantao Xin Huaping liu Pengxiang Hou Chang liu Maoshuai He Jin Zhang State Key Laboratory of Eco-Chemical Engineering Ministry of EducationTaishan Scholar Advantage and Characteristic Discipline Team of EcoChemical Process and TechnologyCollege of Chemistry and Molecular EngineeringQingdao University of Science and TechnologyQingdao 266042China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Center for Nanochemistry Beijing Science and Engineering Center for NanocarbonsBeijing National Laboratory for Molecular SciencesCollege of Chemistry and Molecular EngineeringPeking UniversityBeijing 100871China School of Science Dalian Maritime UniversityDalian 116026China

Bulk synthesis of single-walled carbon nanotubes(SWNTs)using solid catalyst has been challenging,despite of recent breakthrough in the chirality-specific growth on the flat substrate *** this work,we propose a porous magnesia support rhenium catalyst for bulk synthesis of *** is found that the well-dispersed catalyst with a high melting point and the optimal chemical vapor deposition reaction conditions account for the growth of *** characterizations reveal the produced SWNTs are dominant in(n,n−1)and(n,n−2)***,by using a multicolumn chromatography post-growth separation method,SWNTs with three defined diameter ranges were *** work guides the design of porous oxide supported catalyst for bulk synthesis and diameter-dependent sorting of SWNTs,which will ultimately help harness the extraordinary properties of SWNTs.

关键词： single-walled carbon nanotube rhenium catalyst bulk growth gel chromatography diameter separation