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Structural bonding-breakage constitutive model for natural unsaturated clayey soils

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Acta Mechanica Sinica 2010年第6期26卷 931-939页

作者： Guo-Qing cai Cheng-Gang Zhao xiao-Ming Qin Department of Geotechnique.School of Civil Engineering and Architecture Beijing Jiaotong University Beijing 100044China Hydro China Zhongnan Engineering Corporation Changsha 410014China

The natural clayey soils are usually structural and unsaturated,which makes their mechanical properties quite different from the remolded saturated soils.A structural constitutive model is proposed to simulate the bonding-breakage *** this model,the unsaturated soil element is divided into a cementation element and a friction element according to the binary medium theory,and the stress-strain coordination for these two elements is obtained. The cementation element is regarded as elastic,whereas the friction element is regarded as elastoplastic which can be described with the Gallipoli＇s *** theoretical formulation is verified with the comparative experiments of isotropic compressions on the saturated and unsaturated structural *** analyses of the effects of damage variables on the model predictions are further carried out,which show that breakage deformation of natural clayey soils increases with the rising amount of initial defects.

关键词： Unsaturated clayey soils Structure Micro-mechanism of bonding-breakage Constitutive model

In situ growth of phosphorized ZIF-67-derived amorphous CoP/Cu_(2)O@CF electrocatalyst for efficient hydrogen evolution reaction

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Frontiers of Chemical Science and Engineering 2023年第10期17卷 1430-1439页

作者： Ruiwen Qi xiao Liu Hongkai bu Xueqing Niu xiaoyang Ji Junwei Ma Hongtao Gao Key Laboratory of Optic-Electric Sensing and Analytical Chemistry for Life Sciences MOECollege of Chemistry and Molecular EngineeringQingdao University of Science and TechnologyQingdao 266042China

Transition metal phosphides have been extensively studied for catalytic applications in water ***,we report an in situ phosphorization of zeolitic imidazole frameworks(ZIF-67)to generate amorphous cobalt phosphide/ZIF-67 heterojunction on a self-supporting copper foam(CF)substrate with excellent performance for hydrogen evolution reaction(HER).The needleleaf like copper hydroxide was anchored on CF surface,which acted as implantation to grow *** intermediate product was phosphorized to obtain final electrocatalyst(CoP/Cu_(2)O@CF)with uniform particle size,exhibiting a rhombic dodecahedron structure with wrinkles on the *** electrochemical measurement proved that CoP/Cu_(2)O@CF catalyst exhibited excellent HER activity and long-term stability in 1.0 mol·L^(–1)KOH *** overpotential was only 62 mV with the Tafel slope of 83 mV·dec^(–1)at a current density of 10 mA·cm^(–2),with a large electrochemical active surface *** also showed competitive performance at large current which indicated the potential application to industrial water electrolysis to produce ***-principle calculations illustrated that benefit from the construction of CoP/ZIF-67 heterojunction,the d-band center of CoP downshifted after bonding with ZIF-67 and the Gibbs free energy(ΔGH*)changed from–0.18 to–0.11 eV,confirming both decrease in overpotential and excellent HER *** work illustrates the efficient HER activity of CoP/Cu_(2)O@CF catalyst,which will act as a potential candidate for precious metal electrocatalysts.

关键词： CoP/Cu_(2)O@CF electrocatalyst phosphorization HER DFT

Highly active sites of low spin Fe^(Ⅱ)N_(4)species:The identification and the ORR performance

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Nano Research 2021年第1期14卷 122-130页

作者： Huizhu cai Bingbing Chen xiao Zhang Yuchen Deng Dequan xiao Ding Ma Chuan Shi State Key Laboratory of Fine Chemicals College of Chemical EngineeringDalian University of TechnologyDalian 116024China College of Chemistry and Molecular Engineering and College of Engineering Peking UniversityBeijing 100871China Center for Integrative Materials Discovery Department of Chemistry and Chemical EngineeringUniversity of New HavenCT 06516USA

Over recent years,catalytic materials of Fe-N-C species have been recognized being active for oxygen reduction reaction(ORR).However,the identification of active site remains challenging as it generally involves a pyrolysis process and mixed components being *** Fe_(3)C/C and Fe_(2)N/C samples were synthesized by temperature programmed reduction of Fe precursors in 15%CH_(4)/H_(2)and pure NH_(3),*** acid leaching of Fe_(2)N/C sample,only single sites of FeN_(4)species were presented,providing an ideal model for identification of catalytic functions of the single sites of FeN_(4)in ORR.A correlation was conducted between the concentration of Fe^(Ⅱ)N_(4)in low spin state by Mossbauer spectra and the kinetic current density at 0.8 V in alkaline media,and such a structure-performance correlation assures the catalytic roles of low spin Fe^(Ⅱ)N_(4) species as highly active sites for the ORR.

关键词： single sites of FeN_(4) oxygen reduction reaction structure-performance correlation electrocatalysis

Regression Analysis of Doubly Censored Data with a Cured Subgroup under a Class of Promotion Time Cure Models

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Acta Mathematica Sinica,English Series 2021年第6期37卷 835-853页

作者： Min cai Li Qun xiao Shu Wei LI School of Economics and Statistics Guangzhou UniversityGuangzhou 510006P.R.China

In some situations,the failure time of interest is defined as the gap time between two related events and the observations on both event times can suffer either right or interval *** data are usually referred to as doubly censored data and frequently encountered in many clinical and observational ***,there may also exist a cured subgroup in the whole population,which means that not every individual under study will experience the failure time of interest *** this paper,we consider regression analysis of doubly censored data with a cured subgroup under a wide class of flexible transformation cure ***,we consider marginal likelihood estimation and develop a two-step approach by combining the multiple imputation and a new expectation-maximization(EM)algorithm for its *** resulting estimators are shown to be consistent and asymptotically *** finite sample performance of the proposed method is investigated through simulation *** proposed method is also applied to a real dataset arising from an AIDS cohort study for illustration.

关键词： Doubly censored data marginal likelihood EM algorithm multiple imputation transformation cure models

Amphiphilic miktoarm star copolymers can self-assemble into micelle-like aggregates in nonselective solvents: a case study of polyoxometalate based miktoarm stars

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Science China Chemistry 2020年第6期63卷 792-801页

作者： Jie xiao Qun He Shengchao Qiu Haoquan Li Binghua Wang Bin Zhang Weifeng bu Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province State Key Laboratory of Applied Organic Chemistryand College of Chemistry and Chemical EngineeringLanzhou UniversityLanzhou 730000China State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical PhysicsChinese Academy of SciencesLanzhou 730000China School of Materials Science&Engineering Zhengzhou UniversityZhengzhou 450002China

It is well-known that amphiphilic star-shaped copolymers can self-assemble in selective solvents to form complicated micellar constructs as a synergistic result of both the topological constraints and relative volume fractions of the *** the association phenomena of amphiphilic stars have been observed in nonselective solvents,both the structural detail and formation mechanism of these associates are not clear ***,these experimental observations are controversial with respect to molecularly dispersed starlike copolymers in nonselective solvents as is popularly *** clarify these issues,we have synthesized a series of polyoxometalate-based polystyrene-poly(ethylene glycol)(PS-PEG)miktoarm star supramolecular copolymers(SEW-1–5)by coupling a Keggin-type polyoxometalate of K4[α-SiW12O40]with 1,2,3-triazolium bridged block copolymers of-PSn-b+-PEGmI-(n=17,26,39,57,81;m=45)through ionic exchange reactions,*** imaging,contact angle and 1H NMR studies reveal that SEW-2–5 self-assemble in chloroform,THF,and toluene to create micellelike aggregates ranging from cylinder to sphere with a PS corona and a PEG core,while for SEW-1,reverse bilayers are captured with a PEG corona and a PS *** these aggregates,the Keggin clusters of[α-SiW12O40]4-localize at the core-corona interfaces between PS and *** terms of solvent quality,chloroform,THF,and toluene are only slightly poorer for PEG than that for PS with a relative order of chloroform

关键词： miktoarm star copolymer self-assembly micellelike aggregate nonselective solvent polyoxometalate

Dielectric and ferroelectric characteristics of Ba(Ti_(0.25)Zr_(0.25)Hf_(0.25)Sn_(0.25))O_(3)high-entropy ceramics

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Journal of Materiomics 2023年第4期9卷 634-641页

作者： Rui Hu Mi bu Hang Chen xiao Li Zhu Xiang Ming Chen School of Materials Science and Engineering Zhejiang UniversityHangzhou310027China

Ba(Ti_(0.25)Zr_(0.25)Hf_(0.25)Sn_(0.25))O_(3)high-entropy ceramics were prepared by a standard solid state reaction process,and the dielectric and ferroelectric characteristics were investigated together with the *** X-ray diffraction(XRD)and energy dispersive spectroscopy(EDS)analysis demonstrated a single-phase perovskite structure in the present ceramics.A broad dielectric peak with strong frequency dispersion feature was determined,which indicated the typical relaxor nature originating from the nanoscale ferroelectric domain *** resulted from the structural distortion and chemical disorder due to high-entropy,where the long-range order of ferroelectric domains was *** homogeneous microstructure led to the reduced leakage current density and significantly improved dielectric strength,which was desired for the practical *** with the similar systems of Ba(Ti_(1-x)Zr_(x))O_(3)&Ba(Ti_(1-x)Sn_(x))O_(3),the present high-entropy ceramics indicated better relaxor ferroelectric characteristics.

关键词： High-entropy ceramic Microstructure Perovskite Relaxor ferroelectric

Ultra-high conductive 3D aluminum photonic crystal as sulfur immobilizer for high-performance lithium-sulfur batteries

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Nano Research 2021年第12期14卷 4776-4782页

作者： Jiajia xiao Shengxuan Lin Zihe cai Tahir Muhmood xiaobin Hu State Key Laboratory of Metal Matrix Composites School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghai200240China

The practical application of lithium-sulfur (Li-S) batteries is hampered by the insulative nature of sulfur, sluggish electrochemical kinetics, and large volume variation, which result in capacity-fading at a large current density and poor cycling stability. Herein, a three-dimensional (3D) aluminum photonic crystal encapsulating sulfur (APC@S) composite as a binder-free cathode for Li-S battery is reported. The 3D APC@S cathode can deliver a fantastic capacity of 1,517.8 mAh·g^(−1) at 0.5 C, and retains 712.7 mAh·g^(−1) after 1,500 cycles at 2 C with a decay rate of 0.02% per cycle. Even at a high rate of 5 C, the reversible capacity can still maintain at 680.7 mAh·g^(−1) after 1,000 cycles with a capacity retention of 74.8%. Furthermore, the assembled soft-packaged Li-S battery also exhibits high reversible capacity and stable cycling performance. The excellent electrochemical performance is attributed to the 3D hierarchical and continuously porous structure and high conductive aluminum-wall, which can effectively trap polysulfides, confine the volume expansion on cycling, and accelerate electron/ion transfer. It is expected that this high conductive metal cathode has a great future for the application of energy storage devices.

关键词： lithium-sulfur battery aluminum interconnected ordered high-conductivity photonic crystal

POD analysis on vortical structures in MVG wake by Liutex core line identification

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Journal of Hydrodynamics 2020年第3期32卷 497-509页

作者： Xiang-rui Dong xiao-shu cai Yinlin Dong Chaoqun Liu School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai 200093China Key Laboratory of Multiphase Flow and Heat Transfer in Shanghai Power Engineering Shanghai 200093China Department of Mathematics University of Central ArkansasConway 72035USA Department of Mathematics University of Texas at ArlingtonArlington 76019USA

The Liutex core line method, first combined with the snapshot proper orthogonal decomposition (POD), is utilized in a supersonic micro-vortex generator (MVG) wake flow at Ma = 2.5 and Reθ = 5 760 to reveal the physical significance of each POD mode of the flow field. Compared with other scalar-based vortex identification methods, the Liutex core line identification is verified to be the most appropriate approach that is threshold-free and provides full information of a fluid rotation motion. Meanwhile, the Liutex integration is employed to quantitatively track the evolution of the vortices in MVG wake and is applied to the determination of the effective control section of the MVG wake for the optimization study of MVG design. The physical mechanism of each POD mode for multi-scale and multi-frequency vortical structures is investigated by using Liutex core line identification to give some revelations. For the mean mode (mode 0) indicating the time-averaged velocity flowfield of the MVG wake flow, a pair of primary counter-rotating streamwise vortices and another pair of secondary vortices is uniquely identified by two pairs of Liutex core lines with Liutex magnitude. In contrast, mode 1 is featured by a fluctuated roll-up motion of streamwise vortex, and the streamwise component of the MVG wake is demonstrated to be dominant in terms of the total kinetic energy contribution. Meanwhile, a dominant shedding frequency of St = 0.072 is detected from the temporal behavior of mode 2, which has the organized arc-shaped vortex structures shedding from MVG induced by the K-H instability. Additionally, mode 4 subjects to low-frequency oscillations of the wall vortices and thus takes a relatively lower frequency of St = 0.044.

关键词： Proper orthogonal decomposition(POD) vortex identification Liutex vortex core lines micro-vortex generator(MVG)

Estimation of Fracture Toughness for A508-III Steel in Ductile-to-Brittle Transition Region Using a Strain-Energy–Density-Based Fracture Failure Model

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Acta Mechanica Solida Sinica 2022年第5期35卷 834-841页

作者： Yuanjun Wu Chen Bao Lixun cai Kaiqing Wang xiao Liu Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province School of Mechanics and Aerospace EngineeringSouthwest Jiaotong UniversityChengdu610031China Science and Technology on Reactor Fuel and Materials Laboratory Nuclear Power Institute of ChinaChengdu610213China

According to the assumption of intrinsic relationship between ultimate strain energy density and microcrack nucleation,this work developed a fracture failure model to estimate the fracture toughness of A508-III steel in the ductile-to-brittle transition *** fracture toughness and uniaxial tension tests at different temperatures were carried out to determine the relationship between nucleation parameter and ultimate strain energy density,from which the evolutions of fracture toughness of A508-III ferritic steel for different cumulative failure probabilities at different temperatures were *** fracture failure model can well describe the fracture toughness distribution of A508-III steel in the ductile-to-brittle transition *** with the master curve method,this model has better temperature *** is more convenient to calibrate the parameters of this model compared with the traditional Beremin model,and without complex finite element analysis.

关键词： Fracture toughness Cumulative failure probability A508-III steel Ductile-to-brittle transition region