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Energy conversion characteristics of reciprocating piston quasi- isothermal compression systems using water sprays

Science China(Technological Sciences) 2018年第2期61卷 285-298页

作者： jia guanwei cai maolin xu weiqing shi yan school of automation science and electrical engineering beihang universityBeijing 100191China pneumatic and thermodynamic energy storage and supply beijing key laboratory beihang universityBeijing 100191China

Air compressors are vital and have numerous industrial applications. Approximately 8% of the annual operating electricity consumption in industrial countries is constituted by due to the use of air compressors. Because the poor heat transfer to the environment in the rapid compression process, the compression is non-isothermal, the efficiency of compressors is restricted. To improve their efficiency and achieve isothermal compression, this study proposes energy conversion reciprocating piston quasiisothermal compression using a water spray. First, a mathematical model of a reciprocating piston compressor with water sprays was established. Through experimental investigation and simulations, the mathematical model was validated. The energy conversion characteristics of the reciprocating piston compressor were then studied. To reduce compression power and enhance compression efficiency, it was first discovered that the critical parameters were the input pressure of the driving chamber, water spray mass, and compression volume ratio, which were then evaluated thoroughly. The higher the inlet pressure of the driving chamber, the faster the air compression velocity. Additionally, the compression efficiency was elevated as the water spray mass was gradually increased for a given compression volume ratio. When the compression volume ratio was increased from 2 to 3,the compression power increased from 172.7 J/stroke to 294.2 J/stroke and the compression efficiency was enhanced from 37.3%(adiabatic) to 80.6%. This research and its performance analysis can be referred to during the parameter design optimisation of reciprocating piston quasi-isothermal compression systems using water sprays.

关键词： water spray cooling quasi-isothermal compression compression power compression efficiency

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Evaluating Breakthrough Pressure in Gas Diffusion Layers of Proton Exchange Membrane Fuel Cells

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Journal of Thermal Science 2010年第5期19卷 459-464页

作者： Ma Yue jia Li Zhang Zhuqian Wang xia School of Mechanical and Electroriic Control Engineering Beijing Jiaotong University Beijing 100044 China Department of Mechanical Engineering Oakland University Rochester MI 48309 USA

This paper studied the breakthrough pressure for liquid water to penetrate the gas diffusion layer(GDL) of a proton exchange membrane fuel cell(PEMFC).An ex-situ testing was conducted on a transparent test cell to visualize the water droplet formation and detachment on the surface of different types of GDLs through a CCD *** breakthrough pressure,at which the liquid water penetrates the GDL and starts to form a droplet,was *** breakthrough pressure was found to be different for the GDLs with different porosities and *** equilibrium pressure,which is defined as the minimum pressure required maintaining a constant flow through the GDL,was also *** equilibrium pressure was found to be much lower than the breakthrough pressure for the same type of GDL.A pore network model was modified to further study the relationship between the breakthrough pressure and the GDL properties and *** breakthrough pressure increases for the thick GDL with smaller micro-pore size.

关键词： PEMFC Gas diffusion layer Visualization Network model

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Factors influencing water quality indices in a typical urban river originated with reclaimed water

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Frontiers of Environmental Science & Engineering 2017年第4期11卷 73-82页

作者： jiao Zhang Zhen Wei Haifeng jia xia Huang State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment Tsinghua University Beijing 100084 China

The water quality in a typical urban river segment originated with reclaimed water in Beijing was monitored for two years to investigate the evolution of water quality along the rivcr, and statistical analysis was applied to determine factors influencing water quality of such river recharged by reclaimed water. It was found that no significant change in pollutant concentrations （including COD, NH4＋-N, TN and TP） was observed during this time, and their average values were close to those of the original reclaimed water. However, turbidity and algal contents fluctuated temporally in the direction of river flow. Statistical analysis showed that turbidity was strongly positively correlated with algal contents for flow rate 〈 0.1 m.s-1. whereas it was strongly positively correlated with both algalcontents and TOC for flow rate 〉 0. 1m. s-1. It was observed that diatom was the absolute predominant phyla with Melosira as the major species. In terms of algal bloom control, the specific growth rate of algae was strongly correlated to temperature, and was influenced by flow rate as well. Compared with two other rivers originated with reclaimed water and one originated with natural water, the Shannon Wiener index in the objective river was the lowest, with values between 0.7 and 1.6, indicating a high risk for algal bloom. Statistics showed that Shannon Wiener index was strongly negatively correlated to nutrient salts and cations.

关键词： Reclaimed water Urban river Turbidity Algae Flow rate

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Resource allocation in OFDMA heterogeneous networks for maximizing weighted sum energy efficiency

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Science China(Information Sciences) 2017年第6期60卷 200-211页

作者： xiaoming WANG Fuchun ZHENG xia jia xiaohu YOU School of Telecommunication and Information Engineering Nanjing University of Posts and Telecommunications National Mobile Communications Research Laboratory Southeast University School of Systems Engineering University of Reading Tongda College of Nanjing University of Posts and Telecommunications

In this paper, a resource allocation algorithm for maximizing the weighted sum energy efficiency(EE) is investigated in orthogonal frequency division multiple access(OFDMA) heterogeneous networks(HetNets). We aim to balance the EE of macro cell and low power nodes by subchannel and power allocations. We formulate the problem as a nonlinear sum-of-ratios programming issue, and guarantee data rate requirements of users by using minimum rate constraints. Due to the nonconvexity of the problem, we develop a heuristic subchannel assignment algorithm, and then solve the power allocation problem by parameterized transformations and a first-order approximation based on an iterative algorithm. Numerical results illustrate the convergence and the effectiveness of the proposed algorithm.

关键词： resource allocation energy efficiency OFDMA heterogeneous network interference management

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Origin of High Elastic Recovery of Hard-elastic Polypropylene Film at Room Temperature: the Mixed Contribution of Energy Elasticity and Entropy Elasticity

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Chinese Journal of Polymer Science 2020年第12期38卷 1325-1334页

作者： jia-Yi Xie Rui-Jie Xu cai-Hong Lei Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter Guangdong Provincial Engineering Laboratory of Energy Storage Materials and DevicesSchool of Materials and EnergyGuangdong University of TechnologyGuangzhou 510006China

The crystalline and amorphous regions were alternately arranged in the hard elastic polypropylene(PP)films with row-nucleated *** this work,their structure evolution during stretching and recovery at room temperature was followed and the elastic recovery mechanism was discussed by twice cyclic tensile *** the first stretching to 100%,the lamellae crystals are parallel separated and the intercrystallite crazing is formed at the first yield *** nano-cavities within the intercrystallite crazing appear when the strain reaches 20%.The strain-hardening process accompanies with the lamellae long period increasing and the intercrystallite crazing *** the secondary yield point,the lamellae cluster is further separated and more nano-cavities *** first and second recovery processes are complete *** recovery,firstly,the energy elasticity provided by nano-cavities surface tension drives the shrinkage of material,and then the entropy elasticity related to amorphous chain relaxation plays a leading role when the strain is smaller than the secondary yield *** elastic recovery process of hard elastic material is the co-contribution of energy elasticity and entropy *** work gives a clearer recognition about the source of hard elastic property and the role of amorphous region in material's deformation.

关键词： Hard-elastic material Elastic recovery Entropy elasticity Energy elasticity

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Plasmonic nanostructures acting as a light-driven O_(2)-sensitive nitroreductase mimic for enhanced photochemical oxidation of para-aminothiophenol

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Nano Research 2023年第11期16卷 12697-12705页

作者： Xinshuang Gao jia-jia Zheng Hanbo Li Rui cai Xingfa Gao xiaochun Wu CAS Key Laboratory of Standardization and Measurement for Nanotechnology National Center for Nanoscience and TechnologyBeijing 100190China Laboratory of Theoretical and Computational Nanoscience National Center for Nanoscience and TechnologyBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China

Nanozymes,as a novel form of enzyme mimics,have garnered considerable *** overcoming the main disadvantages of their natural analogs,they still face challenges such as restricted mimic types and low substrate ***,we introduce a reactive ligand modification strategy to diversify enzyme mimic ***,we have utilized helical plasmonic nanorods(HPNRs)modified with para-nitrothiophenol(4-NTP)to create an oxygen-sensitive nitroreductase(NTR)with *** act as a light-adjustable source of nicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide phosphate(NAD(P)H),providing photon-generated energetic electrons to adsorbed 4-NTP *** the presence of O_(2),the activated 4-NTP transfers the captured electron to the adsorbed O_(2),mimicking the electron transfer process in its natural *** enhanced O_(2)activation notably boosts the oxidative coupling of para-aminothiophenol(4-ATP).Density functional theory(DFT)calculations reveal that hot electrons injected into the lowest unoccupied molecular orbital(LUMO)energy level of 4-NTP can be transferred to that of molecular *** conclusion,our findings underline the potential of the reactive ligand modification strategy in developing new types of enzyme reactions,which opens up promising avenues for the enhancement and diversification of nanozyme functionalities.

关键词： plasmonic nanostructure nanozyme nitroreductase para-nitrothiolphenol hot electron injection para-aminothiolphenol

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Selective interfacial bonding and thermal conductivity of diamond/Cu-alloy composites prepared by HPHT technique

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International Journal of Minerals,Metallurgy and Materials 2012年第4期19卷 364-371页

作者： Hui Chen Cheng-chang jia Shang-jie Li xian jia xia Yang School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China Shenzhen Haimingrun Industrial Co. Ltd. Shenzhen 518126 China

Cu-based and Cu-alloy-based diamond composites were made by high-pressure-high-temperature （HPHT） sintering with the aim of maximizing the thermal conductivity of the composites. Improvements in interfacial bonding strength and thermo-physical properties of the composites were achieved using an atomized copper alloy with minor additions of Co, Cr, 13, and Ti. The thermal conductivity （TC） oh- mined exhibited as high as 688 W.m-1.K-1, but also as low as 325 W.m-1.K-l. A large variation in TC can be rationalized by the discrepancy of diamond-matrix interfacial bonding. It was found from fractography that preferential bonding between diamond and the Cu-alloy matrix occurred only on the diamond {100} faces. EDS analysis and Raman spectra suggested that selective interfacial bonding may be attributed to amorphous carbon increasing the wettability between diamond and the Cu-alloy matrix. Amorphous carbon was found to significantly affect the TC of the composite by interface modification.

关键词： metallic matrix composites diamonds copper alloys interfacial bonding thermal conductivity

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Relationship between granitic soil particle-size distribution and shrinkage properties based on multifractal method

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Pedosphere 2020年第6期30卷 853-862页

作者： Yujie WEI Xinliang WU Jinwen xia Chongfa cai Soil and Water Conservation Research Centre College of Resources and EnvironmentHuazhong Agricultural UniversityWuhan 430070China National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and ManagementGuangdong Institute of Eco-environmental Science&TechnologyGuangdong Academy of SciencesGuangzhou 510650China

The mechanical properties of granitic residual soils vary with depth due to changes in soil type and heterogeneity caused by *** purpose of this study was to relate the spatial variation of particle-size distribution(PSD)of granitic soils with soil shrinkage parameters using multifractal *** heterogeneity of PSD and pedogenic processes were depicted in detail by multifractal *** PSD generally increased with the increase of profile depth in accordance with the variation of single fractal dimension(D)ranging from 2.45 to *** shrinkage limit was greatly influenced by the multifractal dimension parameters,including information dimension(D1)and capacity dimension(D0)(Adjusted R2=0.998,P0.97,root sum of squares<0.1),and the water variation corresponding to the maximum change rate of linear extensibility was determined by the silt content(R2=0.81,P<0.01).Overall,the shrinkage of granitic soils was primarily influenced by PSD and soil compactness.

关键词： bulk density fractal dimension multifractal characteristics shrinkage characteristics soil compactness

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Congruences for finite triple harmonic sums

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第6期8卷 946-948页

作者： FU Xu-dan ZHOU xia cai Tian-xin Department of Mathematics Zhejiang University Hangzhou 310028 China Hangzhou Foreign Language School Hangzhou 310023 China

Zhao （2003a） first established a congruence for any odd prime p〉3, S（1,1,1 ;p）=-2Bp-3 （mod p）, which holds when p=3 evidently. In this paper, we consider finite triple harmonic sum S（α,β, γ,ρ）（modp） is considered for all positive integers α,β, γ. We refer to w=α＋β＋ γ as the weight of the sum, and show that if w is even, S（α,β, γ,ρ）=0 （mod p） for p≥w＋3; if w is odd, S（α,β, γ,ρ）=-rBp-w （mod p） for p≥w, here r is an explicit rational number independent ofp. A congruence of Catalan number is obtained as a special case.

关键词： Finite triple harmonic sums Recursive relation Bernoulli numbers Catalan numbers

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Fluvial sediments in the Alagxa Plateau as a dust source: iron mineralogical and geochemical evidence

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Journal of Arid Land 2019年第2期11卷 217-227页

作者： WANG Youjun jia jia LU Hao LU caichen xia Dunsheng College of Tourism and Environmental Resource Zaozhuang University College of Geography and Environmental Sciences Zhejiang Normal University College of Earth and Environmental Sciences Lanzhou University

The Alagxa Plateau, in the margin of the northeastern Tibetan Plateau, is one of the most important dust source areas in East Asia, and the widespread sandy desert in the area is important both as a reservoir and a source of eolian silty. The northeastern margin of the Tibetan Plateau is one of the most actively-growing mountain belt on earth, and has large amounts of debris, with masses of fine grained material, which were continuously mobilized and deposited in the Alagxa Plateau by rivers, forming broad alluvial fans. It is possible that the role of fluvial sediments as a source of silty dust in the Alagxa Plateau has been underestimated. In this study, we test this hypothesis by investigating the iron mineralogical and geochemical characteristics of the fluvial sediments and the surface material of the sandy desert in the Alagxa Plateau, and comparing them with paleo-eolian dust deposits(loess) in the adjacent Chinese Loess Plateau(CLP) to investigate the possible linkages among the fluvial sediments, sandy desert and the last glacial loess of the CLP. The results show that sandy desert typically have high contents of goethite, and high ratios of goethite to hematite, similar to the fluvial sediments in the Alagxa Plateau. Based on the major element characteristics, field investigations and the results of previous studies, we found a genetic link between the silt component of the fluvial sediments and the sandy desert in the Alagxa Plateau with high value of Gt(goethite) and similarity of the Gt/(Hm(hematite)+Gt) ratio. But the silt component of the sandy desert main come from the adjacent fluvial sediments. The iron mineralogical characteristics(χ(magnetic susceptibility), χARM(anhysteretic susceptibility), SIRM(saturation isothermal remanent magnetization) and SIRM_(AF100 mT)(SIRM demagnetized at 100 mT)) of the CLP samples overlap with those of the fluvial sediments in the Alagxa Plateau, but there is a mismatch with the sandy desert samples. This suggests th

关键词： fluvial sediments silty dust sandy dust iron mineralogical and geochemical characteristic Alagxa Plateau

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