Multicomponent(Hf-Zr-Ta)B_(2)potentially provides improved ablation resistance compared with silicon-based ceramics.Here we deposited(Hf_(0.5-x/2)Zr_(0.5-x/2)Ta_(x))B_(2)(x=0,0.1,and 0.2)coatings onto C/C com-posites,...Multicomponent(Hf-Zr-Ta)B_(2)potentially provides improved ablation resistance compared with silicon-based ceramics.Here we deposited(Hf_(0.5-x/2)Zr_(0.5-x/2)Ta_(x))B_(2)(x=0,0.1,and 0.2)coatings onto C/C com-posites,and investigated their ablation behaviors under an oxyacetylene torch with a heat flux of 2.4 MW m^(-2).It was observed that the x=0.1 oxide scale bulged but was denser,and the x=0.2 oxide scale was blown away due to the formation of excessive liquid.Based on these findings,we further de-veloped a duplex(Hf-Zr-Ta)B_(2)coating that showed a linear recession rate close to zero(0.11μm s^(-1))after two 120-s ablation cycles.It is identified that the resulting oxide scale is mainly composed of(Hf,Zr)_(6)Ta_(2)O_(17)and(Hf,Zr,Ta)O_(2)by performing aberration-corrected(scanning)transmission electron microscopy.The protective mechanism is related to the peritectic transformation of orthorhombic-(Hf,Zr)_(6)Ta_(2)O_(17)to tetragonal-(Hf,Zr,Ta)O_(2)plus Ta-dominated liquid.This study contributes to the develop-ment of Ta-containing multicomponent UHTC bulk and coatings for ultra-high temperature applications.展开更多
Inhibiting the “shuttle effect” of soluble polysulfides and improving reaction kinetics are the key factors necessary for further exploration of high-performance Li-S batteries. Herein, an effective interface engine...Inhibiting the “shuttle effect” of soluble polysulfides and improving reaction kinetics are the key factors necessary for further exploration of high-performance Li-S batteries. Herein, an effective interface engineering strategy is reported, wherein nitriding of an Ni-based precursor is controlled to enhance Li-S cell regulation. The resulting in-situ formed NiO-Ni_(3)N heterostructure interface not only has a stronger polysulfide adsorption effect than that of monomeric NiO or Ni_(3)N but also has a faster Li ion diffusion ability than a simple physical mixture. More importantly, this approach couples the respective advantages of NiO and Ni_(3)N to reduce polarization and facilitate electron transfer during polysulfide reactions and synergistically catalyze polysulfide conversion. In addition, ultrafine nanoparticles are thought to effectively improve the use of additive materials. In summary, Li-S batteries based on this NiO-Ni_(3)N heterostructure have the features of long cycle stability, rapid charging-discharging, and good performance under high sulfur loading.展开更多
Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality...Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.展开更多
A series of Ti_(56.25-x)Zr_(x)Ni_(25)Cu1_(8.75)(x=0–25,at.%) filler metals were designed based on a cluster-plus-glue-atom model to vacuum braze TiAl intermetallic to K4169 alloy. The impact of Zr content on the inte...A series of Ti_(56.25-x)Zr_(x)Ni_(25)Cu1_(8.75)(x=0–25,at.%) filler metals were designed based on a cluster-plus-glue-atom model to vacuum braze TiAl intermetallic to K4169 alloy. The impact of Zr content on the interfacial microstructure and shear strength of joints was examined. And the relationship between the interfacial lattice structure and the fracture behavior of the joint was investigated. The findings reveal a sectionalized characteristic with three reaction zones (Zone I, Zone II and Zone III) in the microstructure of the TiAl intermetallic to K4169 alloy joint. As the Zr content in filler metals increased, the diffusion of Ti transitioned from long-distance to short-distance in Zone I, changing the initial composition from TiNi_(3) /TiNi/NiNb/(Cr, Fe, Ni)SS to NiCrFe/(Cr, Fe, Ni)SS /TiNi. In Zone II, the initial composition altered from TiNi_(3) /TiNi to TiNi/Ti_(2) Ni/TiNi_(3) /TiCu/TiNi. The interface between Zones II and III altered from a non-coherent and semi-coherent interface of TiNi/TiAl/Ti_(3) Al with significant residual stress to a semi-coherent interface of TiNi/TiNi_(3) /TiAl_(2) /Ti_(3) Al with a gradient distribution. The shear strength of the joint initially decreased and then increased. When the Zr content of filler metal was 25 at.%, the shear strength of the joint reached 288 MPa. The crack initiation position changed from non-coherent TiNi/TiAl interface with high angle grain boundaries (HAGBs) and lattice mismatch of 65.86 at.% to a semi-coherent Ti3 Al/TiAl2 interface with a lattice mismatch of 20.07 at.% when the Zr content increased. The brittle fracture was present on the fracture surfaces of all brazed joints.展开更多
Carbon material is an important additive in energetic materials.Graphene is a monolayer carbon material in which carbon atoms are arranged in two-dimensional honeycomb structure,who has special optical,electrical,and ...Carbon material is an important additive in energetic materials.Graphene is a monolayer carbon material in which carbon atoms are arranged in two-dimensional honeycomb structure,who has special optical,electrical,and mechanical properties.Recently,the application of graphene-based composites in energetic materials has received extensive attention.This review mainly summarizes the applications of graphene and graphene-based nanomaterials in energetic materials.The effects of these materials on the thermal stability,sensitivity,mechanical property,ignition and combustion of energetic materials were discussed.Furthermore,the progress of functionalized modification of graphene has been summarized,including covalent bonding modification and doping modification.These studies show that graphenebased materials exhibit excellent performances and might emerge as promising candidate for energetic materials.展开更多
TiAl intermetallic could be used to replace Ni-based alloy in assemblies to generate excellent specific strength.A(Ti,Zr)-Ni-based amorphous filler metal Ti_(21.25)Zr_(25)Ni_(25)Cu_(18.75)(at.%)was designed using a cl...TiAl intermetallic could be used to replace Ni-based alloy in assemblies to generate excellent specific strength.A(Ti,Zr)-Ni-based amorphous filler metal Ti_(21.25)Zr_(25)Ni_(25)Cu_(18.75)(at.%)was designed using a cluster-plus-glue-atom model to successfully vacuum braze K4169 and TiAl bimetallic assemblies.At various brazing temperatures and holding time,the quantitative relationships between lattice distortion,grain boundary,dislocation density,and hardness,elastic modulus,shear strength of the joints were investigated.Meanwhile,the fracture mechanism of the joints was revealed.The brazed seam mainly consisted of solid diffusion reaction layers(ZonesⅠandⅢ)and filler metal residue zone(ZoneⅡ).When the brazing temperature increased to 1030℃,grain refinement occurred in the brazed seam.ZoneⅠwas primarily composed of(Ni)ss[0-11]+TiNi[011]/(Cr,Fe,Ni)ss[0-11]/(Ti,Zr)Ni[0-1-1]+(Cr,Fe,Ni)ss[0-11].The(Ti,Zr)(Ni,Cu)[001]and(Ti,Zr)(Ni,Cu)[101]intermetallic compound-based solid solutions were formed in ZoneⅡ.And the lattice distortion of(Ti,Zr)(Ni,Cu)[101]and(Ti,Zr)(Ni,Cu)[001]was 32.05%and 14.82%,respectively.As a result,the proportion of low angle grain boundaries(LAGBs)and deformed grains in ZoneⅡrose to 38.6%and 38.7%.In ZonesⅠandⅢ,the proportion of LAGBs reduced to 8%and 3.4%,respectively.As the holding time increased,the long-range diffusion of Al in ZoneⅡcaused the(Ti,Zr)(Ni,Cu)[001]with cubic structure to transform into(Ti,Zr)(Ni,Cu,Al)[00-1]with hexagonal crystal system structure,where the lattice distortion was 4.42%and 10.49%for a and c.At 1030℃/10 min,the average geometrically nec-essary dislocation densities(GNDs)in ZonesⅠ,ⅡandⅢwere 9.87×10^(14)m^(-2),8.55×10^(14)m^(-2)and 11.4×10^(14)m^(-2),respectively.Therefore,the shear strength of joints reached 322 MPa due to the lattice distortion,dislocation strengthening and fine grain strengthening.Meanwhile,the plastic and brittle hard phases were generated in ZoneⅡand displayed a mechanical interlocking structure that contributed to the performance of the joint.Both(Ti,Zr)(Ni,Cu)[001]and(Ti,Zr)(Ni,Cu)[101]in ZoneⅡformed along differ-ent low-index cleavage planes during transgranular fracture.The cracks initiated in this region extended to the interface between Zones I andⅡand exhibited bimodal grain characteristics.展开更多
Because of global warming,people have paid more attention to greenhouse gas emitted by vehicles.To quantify the impact of temperature on vehicle CO_(2)emissions,this study was conducted using the world light vehicle t...Because of global warming,people have paid more attention to greenhouse gas emitted by vehicles.To quantify the impact of temperature on vehicle CO_(2)emissions,this study was conducted using the world light vehicle test cycle on two light-duty E10 gasoline vehicles a ambient temperatures of-10,0,23,and 40℃,and found that CO_(2)emission factors of Vehicle1 in the low-speed phase were 22.07%and 20.22%higher than those of Vehicle 2 at cold star and hot start under-10℃.The reason was vehicle 1 had a larger displacement and more friction pairs than vehicle 2.There was the highest CO_(2)emission at the low-speed phase due to low average speed,frequent acceleration,and deceleration.The CO_(2)temperature factor and the ambient temperature had a strong linear correlation(R2=0.99).According to CO_(2)temperature factors and their relationships,CO_(2)emission factors of other ambien temperatures could be calculated when the CO_(2)emission factor of 23℃was obtained,and the method also could be used to obtain the CO_(2)temperature factors of different vehicles.To separate the effect of load setting and temperature variation on CO_(2)emission quantitatively a method was proposed.And results showed that the load setting was dominant for the CO_(2)emission variation.Compared with 23℃,the CO_(2)emission for vehicle 1 caused by load setting variation were 62.83 and 47.42 g/km,respectively at-10 and 0℃,while those fo vehicle 2 were 45.01 and 35.63 g/km,respectively.展开更多
Ground-level ozone contamination has been globally an urban air quality issue,particularly for China,which has recently made significant progress in purifying its sky.Unregulated exhaust emissions from motor vehicles,...Ground-level ozone contamination has been globally an urban air quality issue,particularly for China,which has recently made significant progress in purifying its sky.Unregulated exhaust emissions from motor vehicles,predominantly carbonyls and volatile organic compounds(VOCs),are among the leading contributors to ozone formation.In this chassislevel study,the unregulated emissions from five China-5 certified gasoline/CNG bi-fuel taxis,along with their ozone forming potential(OFP),were evaluated.It is found that carbonyls and VOCs were mainly emitted during the starting phase no matter the engine was cold or hot.Compared to gasoline,CNG fueling reduced VOCs emissions on a large scale,especially in the starting phase,but had elevated carbonyls.On a fleet average,CNG fueling derived 15%and 46%less OFP than gasoline in cold-and hot-start tests,respectively.VOCs contributed to over 90%of the total OFP of the exhaust.In terms of alleviating ground-level ozone contamination,CNG is a feasible alternative to gasoline on light-duty vehicles.展开更多
Background:The long-term outcomes of patients treated with a Kawashima procedure and keeping the antegrade pulmonary blood flow(AnPBF)in single-ventricle(SV)and interrupted inferior vena cava(IVC)heart disease is stil...Background:The long-term outcomes of patients treated with a Kawashima procedure and keeping the antegrade pulmonary blood flow(AnPBF)in single-ventricle(SV)and interrupted inferior vena cava(IVC)heart disease is still uncertain as yet.Methods:We investigated 18 patients who underwent the Kawashima procedure with SV physiology and an interrupted IVC between January 2009 and June 2018,perioperative,operative and postoperative characteristics were recorded.Results:A total of 18 patients underwent the Kawashima procedure at a median age of 2.7 years(range 0.5–24.7 years),of which 12(66.7%)were male and 6(33.3%)were female.The mean saturation was 76.2±8.5%in preoperative period and 94.2±2.2%in postoperative period.All patients had kept AnPBF.The median duration of mechanical ventilation was 12 h(range 2.5–22.5 h)and the median duration of pleural drainage was 5 days(range 2–27 days).The median hospital stay was 9 days(range 6–70 days).There was no operative death and no mortality was seen in early postoperative period.Follow-up was 100%completed,with an average follow-up period of 6.1±2.7 years(range 1–11 years).4 patients died during the follow-up.The overall 5 and 10 years’survival rates estimated by Kaplan-Meier method were 88%and 68%,respectively.Although there were no significant differences in the duration of postoperative follow-up between the death group and the survival group(p>0.05),the major systemic ventricular end-diastolic diameter(SVEDD)(p=0.018)and the degree of AVVR(p=0.001)showed significant difference between the two groups.The diameters of main pulmonary artery showed significant growth in both the death group(p=0.015)and the survival group(p=0.012)over time.SVEDD had no significant increase in the survival group(p=0.665)but was significantly larger in the death group(p=0.014).Multivariable risk factors of late mortality in patients treated with Kawashima procedure were follow-up AVVR(p=0.044;HR:3.124;95%CI:1.030–9.473)and SVEDD(p=0.031;HR:9.766;95%CI:1.226–77.8).14 patients(100%)were all in New York Heart Association(NYHA)functional class I and the mean saturation was 93±2%at last follow-up.Only one patient finished Fontan completion.Conclusions:The Kawashima procedure with AnPBF can be safely performed with acceptable early and long outcomes.Although some previous studies have shown the risk of pulmonary arteriovenous malformations(PAVMS)after Kawashima procedure in the mid-and long-term,our findings are in contradiction with it.No PAVMs occurred in all the survivors.Kawashima procedure with open AnPBF may be a good option for unsuitable Fontan candidates.展开更多
Propylene glycol-based MWCNT(multi-walled carbon nanotubes)nanofluids were prepared in the framework of a two-step method and by using a suitable PVP(polyvinyl pyrrolidone)dispersant.The BBD(Box-Behnken design)model wa...Propylene glycol-based MWCNT(multi-walled carbon nanotubes)nanofluids were prepared in the framework of a two-step method and by using a suitable PVP(polyvinyl pyrrolidone)dispersant.The BBD(Box-Behnken design)model was exploited to analyze 17 sets of experiments and examine the sensitivity of the absorbance to three parameters,namely the concentration of MWCNT,the SN ratio(mass ratio of carbon nanotubes to sur-factants)and the sonication time.The results have revealed that,while the SN ratio and concentration of MWCNT have a strong effect on the absorbance,the influence of the sonication time is less important.The sta-tistical method of analysis of variance(ANOVA)was further used to determine the F-and p-values of the model.Five experiments were run to validate this approach.Since sample 2 was found to display the greatest absorbance,it was selected for stability monitoring as well as thermal conductivity and viscosity measurements.This sample has been found to be stable;the viscosity decreased with increasing temperature;the addition of MWCNT nano-particles was more effective in improving the thermal conductivity of propylene glycol than other methods in the literature.Moreover,the MWCNT nanofluid based on propylene glycol exhibited higher thermal conductivity at low temperatures.展开更多
Background:This study aims to explore the efficacy of selective unifocalization(UF)for major aortopulmonary collateral arteries(MAPCAs)unifocalization in children with pulmonary atresia with ventricular septal defect(...Background:This study aims to explore the efficacy of selective unifocalization(UF)for major aortopulmonary collateral arteries(MAPCAs)unifocalization in children with pulmonary atresia with ventricular septal defect(PA/VSD).Methods:A retrospective analysis of 13 patients with PA/VSD/MAPCAs who underwent surgery from June 2017 to December 2019.Sex,age,preoperative cardiovascular angiography test results and McGoon ratio were collected.The properties of the collateral arteries were evaluated by angiography,and selective UF for the“dendritic”MAPCAs and ligation of MAPCAs demonstrating distortion and resistance.Results:A total of 13 severe patients underwent one-stage repair,of which 1 case underwent ventricular septal fenestration and died after 2 weeks of ECMO support.The median age was 37 months,and a median weight was 14.0 kg.A right ventricular to aortic systolic pressure ratio(pRV/pAo)of no more than 0.5 was achieved in 12 living patients.Conclusion:Selective unifocalization based on MAPCAs morphology can achieved a good outcome at the early stage.This surgical concept might be provided a novel insight into treatment for some of the subgroups presenting with this complex form of PA/VSD/MAPCAs.展开更多
Brake wear particle(BWP)emissions are considered one of the dominant sources of particulate matter pollution in urban environments.BWP emissions have increased significantly under high-temperature conditions,emerging ...Brake wear particle(BWP)emissions are considered one of the dominant sources of particulate matter pollution in urban environments.BWP emissions have increased significantly under high-temperature conditions,emerging as a focal point of research interest.This study investigates the effect of brake temperatures on BWP emissions.The brake pad materials undergo violent decomposition and oxidation reactions and generate large amounts of incompletely oxidized organic products at temperatures above 475℃.These organic products cause particles below 200 nm to proliferate,and nanoparticles below 40 nm account for the largest contribution of total BWPs.When the friction surface temperature exceeds 475℃,the high-concentration BWPs below 200 nm will agglomerate into larger particles.High temperatures also cause the brake pad surface to delaminate and fragment into particles above 2.5μm.In addition,when the initial brake speed is above 160 km/h,or the brake pressure is above 7 bar,there is a sharp increase in particles below 200 nm.The results suggest that a significant number of nanoparticles below 40 nm are inferred to be generated as the flash temperature of the friction surface reaches the violent reaction temperature.This study provides guidelines for designing low-emission brake pads,as improving the high-temperature resistance of brake pad material components possibly reduces BWP generation.展开更多
The chemical utilization of CO_2 is a crucial step for the recycling of carbon resource. In recent years, the study on the conversion of CO_2 into a wide variety of C_(2+) important chemicals and fuels has received co...The chemical utilization of CO_2 is a crucial step for the recycling of carbon resource. In recent years, the study on the conversion of CO_2 into a wide variety of C_(2+) important chemicals and fuels has received considerable attention as an emerging technology. Since CO_2 is thermodynamically stable and kinetically inert, the effective activation of CO_2 molecule for the selective transformation to target products still remains a challenge. The welldesigned CO_2 reduction route and efficient catalyst system has imposed the feasibility of CO_2 conversion into C_(2+) chemicals and fuels. In this paper, we have reviewed the recent advances on chemical conversion of CO_2 into C_(2+) chemicals and fuels with wide practical applications, including important alcohols, acetic acid, dimethyl ether, olefins and gasoline. In particular, the synthetic routes for C\\C coupling and carbon chain growth, multifunctional catalyst design and reaction mechanisms are exclusively emphasized.展开更多
发热伴血小板减少综合征(severe fever with thrombocytopenia syndrome,SFTS)是一种新发传染病,主要通过蜱虫叮咬传播,其病原体为发热伴血小板减少综合征病毒(severe fever with thrombocytopenia syndrome virus,SFTSV)。人际传播引发...发热伴血小板减少综合征(severe fever with thrombocytopenia syndrome,SFTS)是一种新发传染病,主要通过蜱虫叮咬传播,其病原体为发热伴血小板减少综合征病毒(severe fever with thrombocytopenia syndrome virus,SFTSV)。人际传播引发的SFTS聚集性疫情在国内外均有报道,人们重点关注了人际传播的感染途径,然而SFTS聚集性疫情和病毒基因型之间的相关性研究却未见报道。本文主要报道了2022~2023年河南省信阳市发生的两起SFTS聚集性疫情,探讨了SFTSV出现人际传播感染的可能途径,并对SFTS聚集性疫情与病毒基因型进行了关联分析。通过4例确诊患者的病毒序列分析,发现两起聚集性疫情中的2组SFTSV分别聚集在隶属于不同基因型的两个分支。将本研究病毒序列与GenBank中获得的SFTS聚集性疫情报道过的病毒序列进行系统发育分析,进一步发现人际传播病例报道的SFTSV涉及3种基因型,提示SFTS聚集性疫情的发生可能和病毒基因型无明显关联。本研究表明血液接触感染可能是SFTS聚集性疫情发生的主要传播途径,为揭示SFTS聚集性疫情的人际传播链提供了遗传学证据,为SFTS的人际传播防控提供了科学数据支撑。展开更多
Phototheranostics have attracted tremendous attention in cancer diagnosis and treatment because of the noninvasiveness and promising effectiveness.Developing advanced phototheranostic agents with long emission wavelen...Phototheranostics have attracted tremendous attention in cancer diagnosis and treatment because of the noninvasiveness and promising effectiveness.Developing advanced phototheranostic agents with long emission wavelength,excellent biocompatibility,great tumor-targeting capability,and efficient therapeutic effect is highly desirable.However,the mutual constraint between imaging and therapeutic functions usually hinders their wide applications in biomedical field.To balance this contradiction,we herein rationally designed and synthesized three novel tumor-targeted NIR-Ⅱ probes(QR-2PEG_(321),QR-2PEG_(1000),and QR-2PEG_(5000)) by conjugating three different chain lengths of PEG onto an integrin α_(v)β_(3)-targeted NIR-Ⅱ heptamethine cyanine fluorophore,respectively.In virtue of the essential amphiphilic characteristics of PEG polymers,these probes display various degree of aggregation in aqueous buffer accompanying with differential NIR-Ⅱ imaging and photothermal(PTT) therapeutic performance.Both in vitro and in vivo results have demonstrated that probe QR-2PEG_(5000) has the best NIR-Ⅱ imaging performance with prominent renal clearance,whereas QR-2PEG_(321)possesses excellent photoacoustic signal as well as PTT effect,which undoubtedly provides a promising toolbox for tumor diagnosis and therapy.We thus envision that these synthesized probes have great potential to be explored as a toolkit for precise diagnosis and treatment of malignant tumors.展开更多
Poly-lactic acid(PLA) is widely used as a controlled drug release material and the diffusion property of water within the polymer matrix is closely related to the drug release profile. This paper studies the water dif...Poly-lactic acid(PLA) is widely used as a controlled drug release material and the diffusion property of water within the polymer matrix is closely related to the drug release profile. This paper studies the water diffusion in PLA by molecular dynamic simulations. Free volume analysis indicates that water molecules are expected to fill in the free volumes of the polymer matrix forming water clusters at low water content. Along with the increase of the water concentration, the polymer starts to swell and the density of the system starts to drop.Due to the high mobility of water within water cluster, the calculated diffusion coefficient dramatically increases along with the incensement of water content. Thus, we conclude that the diffusion of water is a self-accelerate process, with higher mobility of water in the case where more water exists.展开更多
The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and...The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.展开更多
In this study,comparing multiple models of machine learning,a multiple linear regression(MLP),multilayer feed-forward artificial neural network(BP)model,and a radial-basis feed-forward artificial neural network(RBF-BP...In this study,comparing multiple models of machine learning,a multiple linear regression(MLP),multilayer feed-forward artificial neural network(BP)model,and a radial-basis feed-forward artificial neural network(RBF-BP)model are selected for the optimization of the thermal properties of TiO_(2)/water nanofluids.In particular,the least squares support vector machine(LS-SVM)method and radial basis support vector machine(RB-SVM)method are implemented.First,curve fitting is performed by means of multiple linear regression in order to obtain bivariate correlation functions for thermal conductivity and viscosity of the nanofluid.Then the aforementioned models are used for a predictive analysis of the dependence of its thermal conductivity and viscosity on temperature and volume fraction.The results show that the least squares support vector machine(LS-SVM)has a prediction accuracy higher than the other models.The model predicts the thermal conductivity of TiO_(2)/water MSE=1.0853×10^(-6),R2=0.99864,MAE=0.00092,RMSE=0.00104,and the viscosity of TiO_(2)/water MSE=8.1397×10^(-6),R2=0.99995,MAE=0.00074,RMSE=0.0009.展开更多
基金supported by the National Key R&D Pro-gram of China(Grant No.2021YFA0715803)the National Natural Science Foundation of China(Grant Nos.52293373,52130205,and 52302091)+1 种基金the Joint Fund of Henan Province Science and Technol-ogy R&D Program(No.225200810002)the ND Basic Research Funds of Northwestern Polytechnical University(No.G2022WD).
文摘Multicomponent(Hf-Zr-Ta)B_(2)potentially provides improved ablation resistance compared with silicon-based ceramics.Here we deposited(Hf_(0.5-x/2)Zr_(0.5-x/2)Ta_(x))B_(2)(x=0,0.1,and 0.2)coatings onto C/C com-posites,and investigated their ablation behaviors under an oxyacetylene torch with a heat flux of 2.4 MW m^(-2).It was observed that the x=0.1 oxide scale bulged but was denser,and the x=0.2 oxide scale was blown away due to the formation of excessive liquid.Based on these findings,we further de-veloped a duplex(Hf-Zr-Ta)B_(2)coating that showed a linear recession rate close to zero(0.11μm s^(-1))after two 120-s ablation cycles.It is identified that the resulting oxide scale is mainly composed of(Hf,Zr)_(6)Ta_(2)O_(17)and(Hf,Zr,Ta)O_(2)by performing aberration-corrected(scanning)transmission electron microscopy.The protective mechanism is related to the peritectic transformation of orthorhombic-(Hf,Zr)_(6)Ta_(2)O_(17)to tetragonal-(Hf,Zr,Ta)O_(2)plus Ta-dominated liquid.This study contributes to the develop-ment of Ta-containing multicomponent UHTC bulk and coatings for ultra-high temperature applications.
基金financial support of the Youth Project of the Provincial Natural Science Foundation of Anhui(No. 2008085QE267)the Doctoral Research Initiation Foundation of Anhui Normal University (No. 751973)+2 种基金the National Natural Science Foundation of China (No. 51972162)the Fundamental Research Funds for the Central Universities (No. 0213-14380196)the Science and Technology Project of Nanchang (No. 2017-SJSYS-008)。
文摘Inhibiting the “shuttle effect” of soluble polysulfides and improving reaction kinetics are the key factors necessary for further exploration of high-performance Li-S batteries. Herein, an effective interface engineering strategy is reported, wherein nitriding of an Ni-based precursor is controlled to enhance Li-S cell regulation. The resulting in-situ formed NiO-Ni_(3)N heterostructure interface not only has a stronger polysulfide adsorption effect than that of monomeric NiO or Ni_(3)N but also has a faster Li ion diffusion ability than a simple physical mixture. More importantly, this approach couples the respective advantages of NiO and Ni_(3)N to reduce polarization and facilitate electron transfer during polysulfide reactions and synergistically catalyze polysulfide conversion. In addition, ultrafine nanoparticles are thought to effectively improve the use of additive materials. In summary, Li-S batteries based on this NiO-Ni_(3)N heterostructure have the features of long cycle stability, rapid charging-discharging, and good performance under high sulfur loading.
基金supported by the National Natural Science Foundation of China(51975112,52375412)Fundamental Research Funds for Central Universities(N2203011)。
文摘Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.
基金supported by the National Natural Science Foun-dation of China(Nos.52275314 and 52075074)the Collaborative Innovation Center of Major Machine Manufacturing in Liaoning.
文摘A series of Ti_(56.25-x)Zr_(x)Ni_(25)Cu1_(8.75)(x=0–25,at.%) filler metals were designed based on a cluster-plus-glue-atom model to vacuum braze TiAl intermetallic to K4169 alloy. The impact of Zr content on the interfacial microstructure and shear strength of joints was examined. And the relationship between the interfacial lattice structure and the fracture behavior of the joint was investigated. The findings reveal a sectionalized characteristic with three reaction zones (Zone I, Zone II and Zone III) in the microstructure of the TiAl intermetallic to K4169 alloy joint. As the Zr content in filler metals increased, the diffusion of Ti transitioned from long-distance to short-distance in Zone I, changing the initial composition from TiNi_(3) /TiNi/NiNb/(Cr, Fe, Ni)SS to NiCrFe/(Cr, Fe, Ni)SS /TiNi. In Zone II, the initial composition altered from TiNi_(3) /TiNi to TiNi/Ti_(2) Ni/TiNi_(3) /TiCu/TiNi. The interface between Zones II and III altered from a non-coherent and semi-coherent interface of TiNi/TiAl/Ti_(3) Al with significant residual stress to a semi-coherent interface of TiNi/TiNi_(3) /TiAl_(2) /Ti_(3) Al with a gradient distribution. The shear strength of the joint initially decreased and then increased. When the Zr content of filler metal was 25 at.%, the shear strength of the joint reached 288 MPa. The crack initiation position changed from non-coherent TiNi/TiAl interface with high angle grain boundaries (HAGBs) and lattice mismatch of 65.86 at.% to a semi-coherent Ti3 Al/TiAl2 interface with a lattice mismatch of 20.07 at.% when the Zr content increased. The brittle fracture was present on the fracture surfaces of all brazed joints.
基金funding support from Startup Foundation for Docotors of Yan’an University(Grant No.YAU205040372)Project of Science and Technology Office of Shaanxi Province(Grant No.2023-JC-QN-0152)。
文摘Carbon material is an important additive in energetic materials.Graphene is a monolayer carbon material in which carbon atoms are arranged in two-dimensional honeycomb structure,who has special optical,electrical,and mechanical properties.Recently,the application of graphene-based composites in energetic materials has received extensive attention.This review mainly summarizes the applications of graphene and graphene-based nanomaterials in energetic materials.The effects of these materials on the thermal stability,sensitivity,mechanical property,ignition and combustion of energetic materials were discussed.Furthermore,the progress of functionalized modification of graphene has been summarized,including covalent bonding modification and doping modification.These studies show that graphenebased materials exhibit excellent performances and might emerge as promising candidate for energetic materials.
基金supported by the National Natural Science Foundation of China(Nos.52275314 and 52075074).
文摘TiAl intermetallic could be used to replace Ni-based alloy in assemblies to generate excellent specific strength.A(Ti,Zr)-Ni-based amorphous filler metal Ti_(21.25)Zr_(25)Ni_(25)Cu_(18.75)(at.%)was designed using a cluster-plus-glue-atom model to successfully vacuum braze K4169 and TiAl bimetallic assemblies.At various brazing temperatures and holding time,the quantitative relationships between lattice distortion,grain boundary,dislocation density,and hardness,elastic modulus,shear strength of the joints were investigated.Meanwhile,the fracture mechanism of the joints was revealed.The brazed seam mainly consisted of solid diffusion reaction layers(ZonesⅠandⅢ)and filler metal residue zone(ZoneⅡ).When the brazing temperature increased to 1030℃,grain refinement occurred in the brazed seam.ZoneⅠwas primarily composed of(Ni)ss[0-11]+TiNi[011]/(Cr,Fe,Ni)ss[0-11]/(Ti,Zr)Ni[0-1-1]+(Cr,Fe,Ni)ss[0-11].The(Ti,Zr)(Ni,Cu)[001]and(Ti,Zr)(Ni,Cu)[101]intermetallic compound-based solid solutions were formed in ZoneⅡ.And the lattice distortion of(Ti,Zr)(Ni,Cu)[101]and(Ti,Zr)(Ni,Cu)[001]was 32.05%and 14.82%,respectively.As a result,the proportion of low angle grain boundaries(LAGBs)and deformed grains in ZoneⅡrose to 38.6%and 38.7%.In ZonesⅠandⅢ,the proportion of LAGBs reduced to 8%and 3.4%,respectively.As the holding time increased,the long-range diffusion of Al in ZoneⅡcaused the(Ti,Zr)(Ni,Cu)[001]with cubic structure to transform into(Ti,Zr)(Ni,Cu,Al)[00-1]with hexagonal crystal system structure,where the lattice distortion was 4.42%and 10.49%for a and c.At 1030℃/10 min,the average geometrically nec-essary dislocation densities(GNDs)in ZonesⅠ,ⅡandⅢwere 9.87×10^(14)m^(-2),8.55×10^(14)m^(-2)and 11.4×10^(14)m^(-2),respectively.Therefore,the shear strength of joints reached 322 MPa due to the lattice distortion,dislocation strengthening and fine grain strengthening.Meanwhile,the plastic and brittle hard phases were generated in ZoneⅡand displayed a mechanical interlocking structure that contributed to the performance of the joint.Both(Ti,Zr)(Ni,Cu)[001]and(Ti,Zr)(Ni,Cu)[101]in ZoneⅡformed along differ-ent low-index cleavage planes during transgranular fracture.The cracks initiated in this region extended to the interface between Zones I andⅡand exhibited bimodal grain characteristics.
基金supported by the National Natural Science Foundation of China(No.52172337)the National Engineering Laboratory for Mobile Source Emission Control Technology(No.NELMS2018A17)the National Key Research and Development Project of China(No.2018YFE0106800-001)。
文摘Because of global warming,people have paid more attention to greenhouse gas emitted by vehicles.To quantify the impact of temperature on vehicle CO_(2)emissions,this study was conducted using the world light vehicle test cycle on two light-duty E10 gasoline vehicles a ambient temperatures of-10,0,23,and 40℃,and found that CO_(2)emission factors of Vehicle1 in the low-speed phase were 22.07%and 20.22%higher than those of Vehicle 2 at cold star and hot start under-10℃.The reason was vehicle 1 had a larger displacement and more friction pairs than vehicle 2.There was the highest CO_(2)emission at the low-speed phase due to low average speed,frequent acceleration,and deceleration.The CO_(2)temperature factor and the ambient temperature had a strong linear correlation(R2=0.99).According to CO_(2)temperature factors and their relationships,CO_(2)emission factors of other ambien temperatures could be calculated when the CO_(2)emission factor of 23℃was obtained,and the method also could be used to obtain the CO_(2)temperature factors of different vehicles.To separate the effect of load setting and temperature variation on CO_(2)emission quantitatively a method was proposed.And results showed that the load setting was dominant for the CO_(2)emission variation.Compared with 23℃,the CO_(2)emission for vehicle 1 caused by load setting variation were 62.83 and 47.42 g/km,respectively at-10 and 0℃,while those fo vehicle 2 were 45.01 and 35.63 g/km,respectively.
基金received funding support from the National Natural Science Foundation of China (No.52272342)the National Engineering Laboratory for Mobile Source Emission Control Technology,China (No.NELMS2018A17).
文摘Ground-level ozone contamination has been globally an urban air quality issue,particularly for China,which has recently made significant progress in purifying its sky.Unregulated exhaust emissions from motor vehicles,predominantly carbonyls and volatile organic compounds(VOCs),are among the leading contributors to ozone formation.In this chassislevel study,the unregulated emissions from five China-5 certified gasoline/CNG bi-fuel taxis,along with their ozone forming potential(OFP),were evaluated.It is found that carbonyls and VOCs were mainly emitted during the starting phase no matter the engine was cold or hot.Compared to gasoline,CNG fueling reduced VOCs emissions on a large scale,especially in the starting phase,but had elevated carbonyls.On a fleet average,CNG fueling derived 15%and 46%less OFP than gasoline in cold-and hot-start tests,respectively.VOCs contributed to over 90%of the total OFP of the exhaust.In terms of alleviating ground-level ozone contamination,CNG is a feasible alternative to gasoline on light-duty vehicles.
基金This study was supported by the NationalKey R&D Program of China[2017YFC1308100].
文摘Background:The long-term outcomes of patients treated with a Kawashima procedure and keeping the antegrade pulmonary blood flow(AnPBF)in single-ventricle(SV)and interrupted inferior vena cava(IVC)heart disease is still uncertain as yet.Methods:We investigated 18 patients who underwent the Kawashima procedure with SV physiology and an interrupted IVC between January 2009 and June 2018,perioperative,operative and postoperative characteristics were recorded.Results:A total of 18 patients underwent the Kawashima procedure at a median age of 2.7 years(range 0.5–24.7 years),of which 12(66.7%)were male and 6(33.3%)were female.The mean saturation was 76.2±8.5%in preoperative period and 94.2±2.2%in postoperative period.All patients had kept AnPBF.The median duration of mechanical ventilation was 12 h(range 2.5–22.5 h)and the median duration of pleural drainage was 5 days(range 2–27 days).The median hospital stay was 9 days(range 6–70 days).There was no operative death and no mortality was seen in early postoperative period.Follow-up was 100%completed,with an average follow-up period of 6.1±2.7 years(range 1–11 years).4 patients died during the follow-up.The overall 5 and 10 years’survival rates estimated by Kaplan-Meier method were 88%and 68%,respectively.Although there were no significant differences in the duration of postoperative follow-up between the death group and the survival group(p>0.05),the major systemic ventricular end-diastolic diameter(SVEDD)(p=0.018)and the degree of AVVR(p=0.001)showed significant difference between the two groups.The diameters of main pulmonary artery showed significant growth in both the death group(p=0.015)and the survival group(p=0.012)over time.SVEDD had no significant increase in the survival group(p=0.665)but was significantly larger in the death group(p=0.014).Multivariable risk factors of late mortality in patients treated with Kawashima procedure were follow-up AVVR(p=0.044;HR:3.124;95%CI:1.030–9.473)and SVEDD(p=0.031;HR:9.766;95%CI:1.226–77.8).14 patients(100%)were all in New York Heart Association(NYHA)functional class I and the mean saturation was 93±2%at last follow-up.Only one patient finished Fontan completion.Conclusions:The Kawashima procedure with AnPBF can be safely performed with acceptable early and long outcomes.Although some previous studies have shown the risk of pulmonary arteriovenous malformations(PAVMS)after Kawashima procedure in the mid-and long-term,our findings are in contradiction with it.No PAVMs occurred in all the survivors.Kawashima procedure with open AnPBF may be a good option for unsuitable Fontan candidates.
基金This research is financially supported by the National Natural Science Foundation of China under Contract(No.51966005).
文摘Propylene glycol-based MWCNT(multi-walled carbon nanotubes)nanofluids were prepared in the framework of a two-step method and by using a suitable PVP(polyvinyl pyrrolidone)dispersant.The BBD(Box-Behnken design)model was exploited to analyze 17 sets of experiments and examine the sensitivity of the absorbance to three parameters,namely the concentration of MWCNT,the SN ratio(mass ratio of carbon nanotubes to sur-factants)and the sonication time.The results have revealed that,while the SN ratio and concentration of MWCNT have a strong effect on the absorbance,the influence of the sonication time is less important.The sta-tistical method of analysis of variance(ANOVA)was further used to determine the F-and p-values of the model.Five experiments were run to validate this approach.Since sample 2 was found to display the greatest absorbance,it was selected for stability monitoring as well as thermal conductivity and viscosity measurements.This sample has been found to be stable;the viscosity decreased with increasing temperature;the addition of MWCNT nano-particles was more effective in improving the thermal conductivity of propylene glycol than other methods in the literature.Moreover,the MWCNT nanofluid based on propylene glycol exhibited higher thermal conductivity at low temperatures.
基金This study was supported by the Clinical and Translational Medicine Research Fund(2019XK320050)of the Basic Research Service Fund of the Central Public Welfare Research Institute of the Chinese Academy of Medical Sciences.
文摘Background:This study aims to explore the efficacy of selective unifocalization(UF)for major aortopulmonary collateral arteries(MAPCAs)unifocalization in children with pulmonary atresia with ventricular septal defect(PA/VSD).Methods:A retrospective analysis of 13 patients with PA/VSD/MAPCAs who underwent surgery from June 2017 to December 2019.Sex,age,preoperative cardiovascular angiography test results and McGoon ratio were collected.The properties of the collateral arteries were evaluated by angiography,and selective UF for the“dendritic”MAPCAs and ligation of MAPCAs demonstrating distortion and resistance.Results:A total of 13 severe patients underwent one-stage repair,of which 1 case underwent ventricular septal fenestration and died after 2 weeks of ECMO support.The median age was 37 months,and a median weight was 14.0 kg.A right ventricular to aortic systolic pressure ratio(pRV/pAo)of no more than 0.5 was achieved in 12 living patients.Conclusion:Selective unifocalization based on MAPCAs morphology can achieved a good outcome at the early stage.This surgical concept might be provided a novel insight into treatment for some of the subgroups presenting with this complex form of PA/VSD/MAPCAs.
基金supported by the National Natural Science Foundation of China(Nos.52172337 and 52272342)the Postdoctoral Fellowship Program(Grade B)of China Postdoctoral Science Foundation(No.GZB20240352)the Shuimu Tsinghua Scholar Program of Tsinghua University(No.2023SM230)。
文摘Brake wear particle(BWP)emissions are considered one of the dominant sources of particulate matter pollution in urban environments.BWP emissions have increased significantly under high-temperature conditions,emerging as a focal point of research interest.This study investigates the effect of brake temperatures on BWP emissions.The brake pad materials undergo violent decomposition and oxidation reactions and generate large amounts of incompletely oxidized organic products at temperatures above 475℃.These organic products cause particles below 200 nm to proliferate,and nanoparticles below 40 nm account for the largest contribution of total BWPs.When the friction surface temperature exceeds 475℃,the high-concentration BWPs below 200 nm will agglomerate into larger particles.High temperatures also cause the brake pad surface to delaminate and fragment into particles above 2.5μm.In addition,when the initial brake speed is above 160 km/h,or the brake pressure is above 7 bar,there is a sharp increase in particles below 200 nm.The results suggest that a significant number of nanoparticles below 40 nm are inferred to be generated as the flash temperature of the friction surface reaches the violent reaction temperature.This study provides guidelines for designing low-emission brake pads,as improving the high-temperature resistance of brake pad material components possibly reduces BWP generation.
基金Supported by the National Natural Science Foundation of China(21576272,21476244)"Transformational Technologies for Clean Energy and Demonstration"+2 种基金Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA21030600)the project from Jiangsu Collaborative Innovation Center for Ecological Building Materials and Environmental Protection Equipment(YCXT201607)Youth Innovation Promotion Association(2016046)of CAS
文摘The chemical utilization of CO_2 is a crucial step for the recycling of carbon resource. In recent years, the study on the conversion of CO_2 into a wide variety of C_(2+) important chemicals and fuels has received considerable attention as an emerging technology. Since CO_2 is thermodynamically stable and kinetically inert, the effective activation of CO_2 molecule for the selective transformation to target products still remains a challenge. The welldesigned CO_2 reduction route and efficient catalyst system has imposed the feasibility of CO_2 conversion into C_(2+) chemicals and fuels. In this paper, we have reviewed the recent advances on chemical conversion of CO_2 into C_(2+) chemicals and fuels with wide practical applications, including important alcohols, acetic acid, dimethyl ether, olefins and gasoline. In particular, the synthetic routes for C\\C coupling and carbon chain growth, multifunctional catalyst design and reaction mechanisms are exclusively emphasized.
文摘发热伴血小板减少综合征(severe fever with thrombocytopenia syndrome,SFTS)是一种新发传染病,主要通过蜱虫叮咬传播,其病原体为发热伴血小板减少综合征病毒(severe fever with thrombocytopenia syndrome virus,SFTSV)。人际传播引发的SFTS聚集性疫情在国内外均有报道,人们重点关注了人际传播的感染途径,然而SFTS聚集性疫情和病毒基因型之间的相关性研究却未见报道。本文主要报道了2022~2023年河南省信阳市发生的两起SFTS聚集性疫情,探讨了SFTSV出现人际传播感染的可能途径,并对SFTS聚集性疫情与病毒基因型进行了关联分析。通过4例确诊患者的病毒序列分析,发现两起聚集性疫情中的2组SFTSV分别聚集在隶属于不同基因型的两个分支。将本研究病毒序列与GenBank中获得的SFTS聚集性疫情报道过的病毒序列进行系统发育分析,进一步发现人际传播病例报道的SFTSV涉及3种基因型,提示SFTS聚集性疫情的发生可能和病毒基因型无明显关联。本研究表明血液接触感染可能是SFTS聚集性疫情发生的主要传播途径,为揭示SFTS聚集性疫情的人际传播链提供了遗传学证据,为SFTS的人际传播防控提供了科学数据支撑。
基金financial support from the Training Program of the Major Research Plan of the National Natural Science Foundation of China (No. 91959123)National Natural Science Foundation of China (No. 22077092)+2 种基金Key Research and Development Program of Social Development of Jiangsu Province (No. BE2018655)the Open Project Program of the State Key Laboratory of Radiation Medicine and Protection (Nos. GZK1202132, GZK1202140 and GZK1202017)funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘Phototheranostics have attracted tremendous attention in cancer diagnosis and treatment because of the noninvasiveness and promising effectiveness.Developing advanced phototheranostic agents with long emission wavelength,excellent biocompatibility,great tumor-targeting capability,and efficient therapeutic effect is highly desirable.However,the mutual constraint between imaging and therapeutic functions usually hinders their wide applications in biomedical field.To balance this contradiction,we herein rationally designed and synthesized three novel tumor-targeted NIR-Ⅱ probes(QR-2PEG_(321),QR-2PEG_(1000),and QR-2PEG_(5000)) by conjugating three different chain lengths of PEG onto an integrin α_(v)β_(3)-targeted NIR-Ⅱ heptamethine cyanine fluorophore,respectively.In virtue of the essential amphiphilic characteristics of PEG polymers,these probes display various degree of aggregation in aqueous buffer accompanying with differential NIR-Ⅱ imaging and photothermal(PTT) therapeutic performance.Both in vitro and in vivo results have demonstrated that probe QR-2PEG_(5000) has the best NIR-Ⅱ imaging performance with prominent renal clearance,whereas QR-2PEG_(321)possesses excellent photoacoustic signal as well as PTT effect,which undoubtedly provides a promising toolbox for tumor diagnosis and therapy.We thus envision that these synthesized probes have great potential to be explored as a toolkit for precise diagnosis and treatment of malignant tumors.
基金Supported by the Scientific Developing Foundation of Tianjin Municipal Education Commission(2017SK055)the Project Grants 521 Talents Cultivation of Zhejiang Sci-Tech University
文摘Poly-lactic acid(PLA) is widely used as a controlled drug release material and the diffusion property of water within the polymer matrix is closely related to the drug release profile. This paper studies the water diffusion in PLA by molecular dynamic simulations. Free volume analysis indicates that water molecules are expected to fill in the free volumes of the polymer matrix forming water clusters at low water content. Along with the increase of the water concentration, the polymer starts to swell and the density of the system starts to drop.Due to the high mobility of water within water cluster, the calculated diffusion coefficient dramatically increases along with the incensement of water content. Thus, we conclude that the diffusion of water is a self-accelerate process, with higher mobility of water in the case where more water exists.
基金financially supported by National Natural Science Foundation of China,China (Grant No.52022012)National Key R&D Program for Young Scientists of China,China (Grant No.2022YFC3080900)。
文摘The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.
基金supported by the National Natural Science Foundation of China(Nos.51966005,51866003)Yunnan Basic Research Program Project(2019FB071).
文摘In this study,comparing multiple models of machine learning,a multiple linear regression(MLP),multilayer feed-forward artificial neural network(BP)model,and a radial-basis feed-forward artificial neural network(RBF-BP)model are selected for the optimization of the thermal properties of TiO_(2)/water nanofluids.In particular,the least squares support vector machine(LS-SVM)method and radial basis support vector machine(RB-SVM)method are implemented.First,curve fitting is performed by means of multiple linear regression in order to obtain bivariate correlation functions for thermal conductivity and viscosity of the nanofluid.Then the aforementioned models are used for a predictive analysis of the dependence of its thermal conductivity and viscosity on temperature and volume fraction.The results show that the least squares support vector machine(LS-SVM)has a prediction accuracy higher than the other models.The model predicts the thermal conductivity of TiO_(2)/water MSE=1.0853×10^(-6),R2=0.99864,MAE=0.00092,RMSE=0.00104,and the viscosity of TiO_(2)/water MSE=8.1397×10^(-6),R2=0.99995,MAE=0.00074,RMSE=0.0009.
