Objective The rising prevalence of childhood obesity is closely associated with suboptimal dietary patterns.To address this public health concern,we conducted a comprehensive study to examine the association between c...Objective The rising prevalence of childhood obesity is closely associated with suboptimal dietary patterns.To address this public health concern,we conducted a comprehensive study to examine the association between coarse cereals consumption and body fat percentage(BFP)in Chinese children and adolescents.Methods The study included 48,305 children aged 6–17 years from 28 districts/counties in 14 provinces across seven regions of China(24,152 girls and 24,153 boys).BFP was examined using bioelectrical impedance analysis in the early morning.Coarse cereals consumption was assessed using a Food Frequency Questionnaire and categorized into three groups:0 g/1,000 kcal per day,0–10 g/1,000kcal per day,and>10 g/1,000 kcal per day(daily consumption of coarse cereals×1,000/total energy consumption).Quantile regression model was used to analyze the association between coarse cereals and BFP,adjusting for potential confounders such as age,pubertal development stage,urban/rural and regional factors,total daily dietary energy consumption,sedentary time,moderate-to-high physical activity,household income,parental education,and consumption of other foods.Results Boys aged 6–10,11–14,and 15–17 years had median daily coarse cereals consumptions of6.6 g,7.1 g,and 5.7 g,with BFP of 19.6%,19.5%,and 17.5%(all P<0.05).Girls in the same age groups showed consumption of 7.1 g,8.4 g,and 6.7 g,with BFP of 20.3%,26.4%,and 31.0%(all P<0.05).The quantile regression results for boys showed that daily consumption of coarse cereals was significantly correlated with their BFP in the 0.15,0.25,and 0.50 quartiles,with regression coefficients of-0.257,-0.221,and-0.330,respectively,after adjusting for potential confounders(P<0.05).For girls,there was a significant correlation with PBF at the 0.05,0.15,0.25,0.50,0.75,and 0.85 quartiles,with regression coefficients of-0.258,-0.366,-0.372,-0.431,-0.472,and-0.503(P<0.05 for all).Conclusions Coarse cereals consumption among Chinese children and adolescents remains relatively low.Higher consumption was inversely associated with BFP in children aged 6–17 years.Future interventional studies should assess how increased coarse cereals consumption prevents childhood obesity.展开更多
Thermodynamic modeling is still themostwidely usedmethod to characterize aerosol acidity,a critical physicochemical property of atmospheric aerosols.However,it remains unclear whether gas-aerosol partitioning should b...Thermodynamic modeling is still themostwidely usedmethod to characterize aerosol acidity,a critical physicochemical property of atmospheric aerosols.However,it remains unclear whether gas-aerosol partitioning should be incorporated when thermodynamicmodels are employed to estimate the acidity of coarse particles.In this work,field measurements were conducted at a coastal city in northern China across three seasons,and covered wide ranges of temperature,relative humidity and NH_(3) concentrations.We examined the performance of different modes of ISORROPIA-II(a widely used aerosol thermodynamic model)in estimating aerosol acidity of coarse and fine particles.The M0 mode,which incorporates gas-phase data and runs the model in the forward mode,provided reasonable estimation of aerosol acidity for coarse and fine particles.Compared to M0,the M1 mode,which runs the model in the forward mode but does not include gas-phase data,may capture the general trend of aerosol acidity but underestimates pH for both coarse and fine particles;M2,which runs the model in the reverse mode,results in large errors in estimated aerosol pH for both coarse and fine particles and should not be used for aerosol acidity calculations.However,M1 significantly underestimates liquid water contents for both fine and coarse particles,while M2 provides reliable estimation of liquid water contents.In summary,our work highlights the importance of incorporating gas-aerosol partitioning when estimating coarse particle acidity,and thus may help improve our understanding of acidity of coarse particles.展开更多
To understand the differences in the composition and sources of PM_(2.5) and PM_(10) caused by coarse particles,integrated PM_(2.5) and PM_(10) samples were synchronously collected in Nanjing,East China,in summer 2020...To understand the differences in the composition and sources of PM_(2.5) and PM_(10) caused by coarse particles,integrated PM_(2.5) and PM_(10) samples were synchronously collected in Nanjing,East China,in summer 2020 and winter 2020/2021.Bulk and molecular speciation and light absorption measurements of aerosol extractswere performed,followed by positivematrix factorization(PMF)based on the PM_(2.5) and PM_(10) data sets,respectively.The difference in average concentrations of total bulk species between PM_(2.5) and PM_(10) was mainly caused by the distribution of considerable NO_(3)^(–),SO42–,Ca^(2+),and organic carbon(OC)in coarse particles.Coarse PMinfluenced by abrasion products from tirewear and leaves contributed about half of the low-volatility n-alkanes in summer.The contribution of coarse PM to biomass burning tracers and water-soluble OC increased in winter when biomass combustion was excessively active.More than 70%of sugar polyols were attributable to coarse PM in summer,and biomass burning could be an important source in winter.The light-absorbing organic chromophores were almost entirely associated with PM_(2.5),but water-soluble organic carbon(WSOC)exhibited stronger light absorption in PM_(10) extracts than in PM_(2.5) extracts possibly due to the influence of coarse PMon pH.PMF analysis indicated that biomass burning,aqueous-phase reactions,and processed dust were the main contributors of organic matter and its light absorption in winter.Biogenic primary and secondary sources made discernable contributions only in summer.The differences between PM_(2.5) and PM_(10) were likely attributed to mixing of crustal dust,combustion particles,and surface reactions.展开更多
The complex grain fragmentation mechanisms of coarse grains in titanium alloys under multi-directional forging(MDF)directly influence the optimization and control of primary hot working processes.This study conducted ...The complex grain fragmentation mechanisms of coarse grains in titanium alloys under multi-directional forging(MDF)directly influence the optimization and control of primary hot working processes.This study conducted MDF experiments onβ-phase as-cast Ti-6554 alloy and simulated non-uniform deformation during cyclic multi-directional compression through macro-and micro-deformation modeling.The results revealed that friction and surface cooling caused low strain and tensile stress concentration at billet edges,leading to mixed grain structures.In contrast,high strain and triaxial compressive stress at billet centers facilitated uniform grain refinement.After 14 compressions and 4 intermediate reheating processes,coarse grains of the billet were refined from 2-5 mm to 0.25-0.50 mm,achieving uniform grain sizes across different regions.For the first time,the orientation evolution of grains with different morphologies during multi-directional compressions was visualized microscopically.Columnar grains were found to be more easily subdivided than equiaxed grains due to local strain accumulation.Under cumulative compressions,grain orientations gradually rotated from uniform to random,driving continuous dynamic recrystallization(CDRX).Slip system interactions and concentrated misorientation led to the formation and extension of transition and shear bands,inducing grain fragmentation dominated by transgranular subdivided CDRX.Smooth grain boundaries transformed into serrated ones after multiple passes,providing additional nucleation sites for discontinuous dynamic recrystallization(DDRX)and facilitating boundary expand CDRX.The interaction of diverse DRX mechanisms was the fundamental cause of grain refinement.This study clarified the principles of refining and homogenizing millimeter-grade coarse grains under increasing forging strain,offering valuable insights for the development of primary hot processing techniques for as-castβtitanium alloys.展开更多
This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace appl...This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.展开更多
This work investigates the influence of carbon residue on the crystallization and solidification behavior of slag at different temperatures and cooling methods as it has a significant impact on the flow and discharge ...This work investigates the influence of carbon residue on the crystallization and solidification behavior of slag at different temperatures and cooling methods as it has a significant impact on the flow and discharge of slag,as well as the proper functioning of gasification equipment.The experimental approach involves the utilization of various techniques,namely ash fusion temperature(AFT)tests,X-ray fluorescence spectroscopy,X-ray diffraction(XRD),scanning electron microscopy(SEM),differential thermal analysis(DSC),and K-value semiquantitative analysis.The results obtained from ash fusion temperature(AFT)tests indicate that the coarse slag exhibits a relatively higher flow temperature compared to the decarburized coarse slag.XRD analysis reveals the presence of diffraction peaks corresponding to Fe and Fe3Si when residue carbon is present in the slag.In contrast,no such peaks are observed in the decarburized coarse slag subjected to the same temperature and cooling mode.This implying that the carbothermal reaction affects the slag's crystallization behavior,consequently influencing the flow temperature in the presence of residual carbon.SEM analysis illustrates that the spheroidization phenomenon is obvious when there is residual carbon in the coarse slag,but there is no spheroidization phenomenon in the decarburized coarse slag.This shows that the surface tension of slag is affected by the presence of residual carbon.Furthermore,DSC results confirm the crystallization transformation and mineral decomposition of the slag at high temperatures.For both carbon-containing slag and decarburized coarse slag,the content of crystals obtained under quenching condition is obviously lower than that under natural cooling condition.展开更多
Coarse woody debris(CWD) plays a crucial role in maintaining biodiversity in forest ecosystems by supporting habitat complexity and influencing soil properties.This study investigates the effects of CWD on gastropod d...Coarse woody debris(CWD) plays a crucial role in maintaining biodiversity in forest ecosystems by supporting habitat complexity and influencing soil properties.This study investigates the effects of CWD on gastropod diversity within managed spruce(Picea abies) forests in the Czech Republic,comparing results to nearby nature reserves(NRs).Gastropod species richness and composition were evaluated at both plot(50 m×50 m) and mesohabitat scales across gradients of CWD and beech(Fagus sylvatica) tree representation.Our results indicate significantly reduced species richness in managed forests(median 7 species per plot) compared to NRs(median15 species),attributed to lower soil pH,calcium availability,and moisture due to the dominance of spruce and the limited availability of CWD.Species richness was positively influenced by CWD volume,with two amounts identified:a minimum of 4 m^(3)·ha^(-1) to prevent significant biodiversity loss and 20 m^(3)·ha^(-1)to support sensitive and dendrophile species.At the within-plot scale,CWD was the species richest mesohabitat,playing a particularly important role in acidic and nutrient-poor environments.Furthermore,beech basal area positively correlated with species richness,mitigating the negative impact of spruce.The findings highlight the critical need for changes in forest management,including increased retention of CWD and integration of deciduous trees,to support biodiversity in intensively managed forests.These measures are particularly urgent given the susceptibility of spruce monocultures to climate change and pest outbreaks.Gastropods,as sessile indicators of environmental change,may serve as effective umbrella species for conservation efforts targeting forest soil biodiversity.展开更多
CGCS(coal gasification coarse slag)and desert sand composite aggregate replacing river sand for the preparation of concrete(coal gasification coarse slag and desert sand composite fine aggregate concrete,abbreviated a...CGCS(coal gasification coarse slag)and desert sand composite aggregate replacing river sand for the preparation of concrete(coal gasification coarse slag and desert sand composite fine aggregate concrete,abbreviated as CDFC)were investigated to study the effect of different CGCS dosages,the sand rate of concrete,and the dosage of fly ash(FA)in cementitious material on the mechanical properties of the concrete and the excessive zone at the aggregate interface.The experimental results show that,with the increase of CGCS admixture,the CDFC water-cement ratio decreases,and the strength shows first increase and then decrease;with the increase of concrete sand rate,the CDFC strength shows first increase and then decrease,and with the increase of FA,the CDFC strength shows first increase and then decrease,when the dosage of cementitious material is 360 kg/m^(3),the composite fine aggregate dosage is 872 kg/m^(3),and the coarse aggregate dosage is 983 kg/m^(3),the maximum compressive strength of its CGCS is 47.4 MPa.The microstructures of CGCS and hydration products were analyzed by X-ray fluorescence spectrometry(XRF),X-ray diffraction(XRD),Fourier transform infrared spectrometry(FTIR),and scanning electron microscopy(SEM).It is found that the CDFC as fine aggregate can generate hydration products such as hydrated calcium silicate gel(C-S-H)in the transition zone of the concrete interface,which can greatly improve the weak zones of the concrete,and improve the strength.展开更多
Hot compression experiments were conducted under conditions of deformation temperatures ranging from 950 to 1150℃,strain rates of 0.001-10 s^(-1),and deformation degrees ranging from 20%to 80%.The hot deformation beh...Hot compression experiments were conducted under conditions of deformation temperatures ranging from 950 to 1150℃,strain rates of 0.001-10 s^(-1),and deformation degrees ranging from 20%to 80%.The hot deformation behavior and microstructure evolution of millimeter-grade coarse grains(MCGs)in the as-cast Ti-6Cr-5Mo-5V-4Al(Ti-6554)alloy were studied,and a hot processing map was established.Under compression along the rolling direction(RD),continuous dynamic recrystallization(CDRX)ensues due to the progressive rotation of subgrains within the MCGs.Along the transverse direction(TD),discontinuous dynamic recrystallization(DDRX)resulting from grain boundary bulging or bridging,occurs on the boundaries of the MCGs.With decreasing strain rate,increasing temperature,and higher deformation degree,dynamic recrystallization becomes more pronounced,resulting in a reduction in the original average grain size.The optimal processing parameters fall within a temperature range of 1050-1150℃,a strain rate of 0.01 s^(-1),and a deformation degree between 40%and 60%.展开更多
After the hot deformation sample of Ti-10V-2Fe-3Al alloy was treated by solid solution in theα+βtwo-phase region,the coarseβgrains that often appeared in theβsingle phase region were observed in the local region,i...After the hot deformation sample of Ti-10V-2Fe-3Al alloy was treated by solid solution in theα+βtwo-phase region,the coarseβgrains that often appeared in theβsingle phase region were observed in the local region,indicating that the abnormal grain growth occurred in the local microstructural region,and the macrostructure also showed abnormally coarse grains(ACGs).The dynamic recrystallization(DRX)behavior of Ti-10V-2Fe-3Al titanium alloy was systematically investigated through hot compression tests on the Gleeble-3800 system.The DRX model ofβgrains was established,and the quantitative correlation between DRX characteristics and the appearance of ACG was clarified.Based on these results,a numerical simulation platform was developed to realize the visual prediction of ACG distribution.The results show that the increase of deformation temperature and the decrease of strain rate both contribute to a significant increase in the grain size(d_(DRX)))and volume fraction(X_(DRX))of DRXed grains.However,the proper X_(DRX)and smaller d_(DRX))at low deformation temperature and high strain rate make the macro and microstructure show ACGs after solid solution.Interestingly,if the DRX degree is excessive or insufficient,ACGs cannot be produced,indicating that ACGs are solid solution products based on the appropriate DRX degree.According to the flow curves and statistical results of microstructure,the quantitative model of DRX kinetics and DRX grain size model were constructed,and the quantitative criterion model that is related to the formation of ACG with grain size(d_(DRX)))and volume fraction(X_(DRX))of DRXed grains as the key parameters was established,i.e.,d_(DRX)≤2.60µm,72.5%≤X_(DRX)≤87.9%.By integrating the subroutine of coarse grain criterion,the isothermal compression process of cylindrical samples and the actual die forging process of H-shaped parts were simulated by DEFORM-3D software of finite element(FE),respectively,and the visual prediction of the distribution of macroscopic ACGs was realized.There is a good consistency between the tested results and the simulated results,indicating a strong correlation between macroscopic ACGs and microscopic DRX.展开更多
Coarse grained WC-9Co cemented carbides with 0-1.0% TaC(mass fraction) were fabricated by HIP-sintering and gas quenching. The effects of TaC on the microstructures and mechanical properties were investigated using sc...Coarse grained WC-9Co cemented carbides with 0-1.0% TaC(mass fraction) were fabricated by HIP-sintering and gas quenching. The effects of TaC on the microstructures and mechanical properties were investigated using scanning electron microscopy(SEM), energy dispersive X-ray analysis(EDS), X-ray diffractometry(XRD) and mechanical properties tests. The results show that the maximum values of hardness and strength are HV 1124 and 2466 MPa respectively when 0.4% TaC is added. When the content of TaC is more than 0.6%, the grain size of WC is no longer affected by the amount of TaC, and(W,Ta)C occurs as well. Moreover, the strength and fracture toughness increase and the(Ta+W) content decreases with the increase of TaC content. The dependence of(Ta+W) content on the mechanical properties indicates that(Ta+W) content in Co should be decreased as low as possible to improve the mechanical properties of coarse grained WC-TaC-9Co cemented carbides with the microstructure of WC+γ two phase regions.展开更多
The high temperature deformation behaviors of α＋β type titanium alloy TC11 （Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） with coarse lamellar starting microstructure were investigated based on the hot compression tests in the tem...The high temperature deformation behaviors of α＋β type titanium alloy TC11 （Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） with coarse lamellar starting microstructure were investigated based on the hot compression tests in the temperature range of 950-1100 ℃ and the strain rate range of 0.001-10 s-1. The processing maps at different strains were then constructed based on the dynamic materials model, and the hot compression process parameters and deformation mechanism were optimized and analyzed, respectively. The results show that the processing maps exhibit two domains with a high efficiency of power dissipation and a flow instability domain with a less efficiency of power dissipation. The types of domains were characterized by convergence and divergence of the efficiency of power dissipation, respectively. The convergent domain in a＋fl phase field is at the temperature of 950-990 ℃ and the strain rate of 0.001-0.01 s^-1, which correspond to a better hot compression process window of α＋β phase field. The peak of efficiency of power dissipation in α＋β phase field is at 950 ℃ and 0.001 s 1, which correspond to the best hot compression process parameters of α＋β phase field. The convergent domain in β phase field is at the temperature of 1020-1080 ℃ and the strain rate of 0.001-0.1 s^-l, which correspond to a better hot compression process window of β phase field. The peak of efficiency of power dissipation in ℃ phase field occurs at 1050 ℃ over the strain rates from 0.001 s^-1 to 0.01 s^-1, which correspond to the best hot compression process parameters of ,8 phase field. The divergence domain occurs at the strain rates above 0.5 s^-1 and in all the tested temperature range, which correspond to flow instability that is manifested as flow localization and indicated by the flow softening phenomenon in stress-- strain curves. The deformation mechanisms of the optimized hot compression process windows in a＋β and β phase fields are identified to be spheroidizing and dynamic recrystallizing controlled by self-diffusion mechanism, respectively. The microstructure observation of the deformed specimens in different domains matches very well with the optimized results.展开更多
To investigate migration and evolution rules of coarse aggregates in the static compaction process, an algorithm of generating digital coarse aggregates that can reflect real morphology（ such as shape, size and fract...To investigate migration and evolution rules of coarse aggregates in the static compaction process, an algorithm of generating digital coarse aggregates that can reflect real morphology（ such as shape, size and fracture surface） of aggregate particles, is represented by polyhedral particles based on the discrete element method（ DEM）. A digital specimen comprised of aggregates and air voids is developed. In addition,a static compaction model consisting of a digital specimen and three plates is constructed and a series of evaluation indices such as mean contact force σMCF, wall stress in direction of zcoordinate σWSZZ, porosity and coordination numbers are presented to investigate the motion rules of coarse aggregates at different compaction displacements of 7. 5, 15 and 30 mm. The three-dimensional static compaction model is also verified with laboratory measurements. The results indicate that the compaction displacements are positively related to σMCF and σWSZZ, which increase gradually with the increase in iterative steps. When the compaction proceeds, the digital specimen porosity decreases, but the coordination number increases. The variation ranges of these four indices are different at different compaction displacements. This study provides a method to analyze the compaction mechanism of particle materials such as asphalt mixture and graded broken stone.展开更多
Quartz, the second most abundant mineral in the earth's crust, is a gangue mineral in practically every flotation process. Coarse quartz flotation has been a long standing problem in various mineral processing pla...Quartz, the second most abundant mineral in the earth's crust, is a gangue mineral in practically every flotation process. Coarse quartz flotation has been a long standing problem in various mineral processing plants to reduce milling cost and increase valuable mineral recovery. Based on this, the effects of nanobubbles(NBs) and hydrodynamic parameters on coarse quartz particle flotation were systematically investigated. Mechanical flotation experiments were carried out using the 7 cm and 9 cm diameter impellers in order to produce different hydrodynamic conditions. 900–1300 rpm impeller speeds were used for the 7 cm diameter impeller and 554–786 rpm for the 9 cm diameter impeller. The results show that the presence of NBs increased the flotation recovery of à425 + 106 lm quartz by up to 21%. For the7 cm diameter impeller, the maximum flotation recoveries of 86.4% and 98% were obtained in the absence and presence of NBs at Reynolds number(Re) of 81,000 and 66,000, respectively. For the 9 cm diameter impeller, the maximum recoveries of 86.3% and 97.5% were obtained in the absence and presence of NBs at Re of 90,000 and 75,000, respectively. NBs increased the flotation rate constant up to 36%.展开更多
A new coarse tuning loop for a wide-band dual-loop frequency synthesizer is presented. The coarse tuning structure is composed of two digital modules, including a successive approximation register and a frequency comp...A new coarse tuning loop for a wide-band dual-loop frequency synthesizer is presented. The coarse tuning structure is composed of two digital modules, including a successive approximation register and a frequency comparator with a novel structure. The frequency comparator counts the prescaler cycles within a certain reference time and compares the number with preset data to estimate the VCO frequency. The frequency comparison error is analyzed in detail. Within a given coarse tuning time,our proposed structure shows a comparison error 20 times smaller than that of other reported structures. This structure also reuses the programmable divider as a part of the coarse tuning loop so that the circuit is greatly simplified.展开更多
Adding polypropylene(PP)fibers and coarse aggregates has become a popular way to enhance the strength and stability of the cemented tailings backfilling(CTB)body.It is essential to explore the influence of tailings-ag...Adding polypropylene(PP)fibers and coarse aggregates has become a popular way to enhance the strength and stability of the cemented tailings backfilling(CTB)body.It is essential to explore the influence of tailings-aggregate ratio and fiber content on the mechanical properties of CTB samples.The comprehensive tests of the unconfined compressive strength(UCS),slump and microstructure were designed,and the regression models were established to characterize the effect of the strength,ductility and fluidity.The results indicate that the tailings-aggregate ratio of 5:5 and PP fiber content of 0.5 kg/m^(3) are the optimum point considering the UCS,cracking strain,peak strain and post-peak ductility.The tailings-aggregate ratio is consistent with the unary quadratic to the UCS and a linear model with a negative slope to the slump.Microstructural analysis indicates that PP fiber tends to bridge the cracks and rod-mill sand to serve as the skeleton of the paste matrix,which can enhance the compactness and improve the ductility of the CTB.The results presented here are of great significance to the understanding and application of coarse aggregates and fibers to improve the mechanical properties of CTB.展开更多
The influence of Nb on microstructure, mechanical property and the transformation kinetics of the coarse grain heat affected zone （CGHAZ） in HSLA steels for different heat inputs, has been investigated. When welded ...The influence of Nb on microstructure, mechanical property and the transformation kinetics of the coarse grain heat affected zone （CGHAZ） in HSLA steels for different heat inputs, has been investigated. When welded at higher heat inputs （100-60 kJ/cm）, impact toughness values of the steel without Nb are much higher than those of the steel with Nb, and the lowest span is 153 J at 60 kJ/cm. But only a little higher values are observed at lower heat inputs （40-30 kJ/cm）, and the highest span is 68 J at 30 kJ/cm. Dilatation studies indicate that continuous cooling transformation starting temperatures （Ts） of CGHAZ for the steel with Nb are approximately 15-30℃ which are lower than those of the steel without Nb at all heat inputs. For higher heat inputs, Nb in solid solution suppresses ferrite transformation and promotes the formation of granular bainite which has detrimental effect on impact toughness. For lower heat inputs higher Charpy impact energy values in the steel with Nb are associated with the formation of low carbon self-tempered martensite.展开更多
The influence of coarse aggregate content on concrete properties was investigated.From the perspective of Frame Concrete Theory,six groups concrete were produced with the same proportion except for coarse aggregate co...The influence of coarse aggregate content on concrete properties was investigated.From the perspective of Frame Concrete Theory,six groups concrete were produced with the same proportion except for coarse aggregate content,with coarse aggregate content of 0%,40%,50%,60%,75%,and 80%,respectively.Slump,compressive and flexural tensile strengths,elastic modulus,and water penetration were tested to research the effect of coarse aggregate content on concrete.The experimental results reveal that slump reduces with increasing of coarse aggregate content,while compressive strength,elastic modulus and flexural tensile strength increase with the coarse aggregate content increasing,and water penetration reduces with coarse aggregate content increasing before 75% then increased.Workability,strength,durability and economical indexes system were established to optimize the coarse aggregate content in concrete based on efficacy coefficient method.The optimization results show that when coarse aggregate content is 60%,the system efficacy coefficient reaches to 0.89,and it expresses the better comprehensive performance.展开更多
Toughness is an important property for steels used in engineering applications. However, recent toughness testing has shown the existence of a significant fluctuation in toughness in a single rolled plate of titanium ...Toughness is an important property for steels used in engineering applications. However, recent toughness testing has shown the existence of a significant fluctuation in toughness in a single rolled plate of titanium micro-alloyed steel. The underlying causes of this fluctuation were investigated by fractography, analysis of microstructure and measurement of inclusions. Coarse and distributed TiN inclusions were responsible for the toughness variation, as they tended to act as the potential cleavage initiators to form micro-cracks. From a calculation of the local fracture stress, the critical size of coarse TiN inclusions for dominating micro-crack propagation was 4.93 μm, and similarly that of ferrite grains was 36.6μm. Under current casting and thermo-mechanically controlled processing schedules, the toughness fluctuation of rolled steel plates can be primarily attributed to the fraction of coarse TiN inclusions larger than 5μm. A corresponding relationship between impact energy and the proportion of coarse TiN inclusions was established. Finally, a normalizing treatment was applied to refine the ferrite grains of rolled steel plates. Despite the presence of coarse TiN inclusions, this refinement in ferrite grains minimized the toughness fluctuation and improved the uniformity of the impact properties of the steel plates.展开更多
Coarse aggregates are the major infrastructure materials of concrete-faced rock-fill dams and are consolidated to bear upper and lateral loads.With the increase of dam height,high confining pressure and complex stress...Coarse aggregates are the major infrastructure materials of concrete-faced rock-fill dams and are consolidated to bear upper and lateral loads.With the increase of dam height,high confining pressure and complex stress states complicate the shear behavfor of coarse aggregates,and thus impede the high dam's proper construction,operation and maintenance.An experimental program was conducted to study the shear behavior of dam coarse aggregates using a large-scale triaxial shear apparatus.Through triaxial shear tests,the strain-stress behaviors of aggregates were observed under constant confining pressures:300 kPa,600 kPa 900 kPa and 1200 kPa.Shear strengths and aggregate breakage characteristics associated with high pressure shear processes are discussed.Stress path tests were conducted to observe and analyze coarse aggregate response under complex stress states.In triaxial shear tests,it was found that peak deviator stresses increase along with confining pressures,whereas the peak principal stress ratios decrease as confining pressures increase With increasing confining pressures,the dilation decreases and the contraction eventually prevails.Initial strength parameters(Poisson's ratio and tangent modulus)show a nonlinear relationship with confining pressures when the pressures are relatively low.Shear strength parameters decrease with increasing confining pressures.The failure envelope lines are convex curves,with clear curvature under low confining pressures.Under moderate confining pressures,dilation is offset by particle breakage.Under high confining pressures,dilation disappears.展开更多
基金supported by the Special Project of National Science and Technology Basic Resources Survey(Grant No.2017FY101100)。
文摘Objective The rising prevalence of childhood obesity is closely associated with suboptimal dietary patterns.To address this public health concern,we conducted a comprehensive study to examine the association between coarse cereals consumption and body fat percentage(BFP)in Chinese children and adolescents.Methods The study included 48,305 children aged 6–17 years from 28 districts/counties in 14 provinces across seven regions of China(24,152 girls and 24,153 boys).BFP was examined using bioelectrical impedance analysis in the early morning.Coarse cereals consumption was assessed using a Food Frequency Questionnaire and categorized into three groups:0 g/1,000 kcal per day,0–10 g/1,000kcal per day,and>10 g/1,000 kcal per day(daily consumption of coarse cereals×1,000/total energy consumption).Quantile regression model was used to analyze the association between coarse cereals and BFP,adjusting for potential confounders such as age,pubertal development stage,urban/rural and regional factors,total daily dietary energy consumption,sedentary time,moderate-to-high physical activity,household income,parental education,and consumption of other foods.Results Boys aged 6–10,11–14,and 15–17 years had median daily coarse cereals consumptions of6.6 g,7.1 g,and 5.7 g,with BFP of 19.6%,19.5%,and 17.5%(all P<0.05).Girls in the same age groups showed consumption of 7.1 g,8.4 g,and 6.7 g,with BFP of 20.3%,26.4%,and 31.0%(all P<0.05).The quantile regression results for boys showed that daily consumption of coarse cereals was significantly correlated with their BFP in the 0.15,0.25,and 0.50 quartiles,with regression coefficients of-0.257,-0.221,and-0.330,respectively,after adjusting for potential confounders(P<0.05).For girls,there was a significant correlation with PBF at the 0.05,0.15,0.25,0.50,0.75,and 0.85 quartiles,with regression coefficients of-0.258,-0.366,-0.372,-0.431,-0.472,and-0.503(P<0.05 for all).Conclusions Coarse cereals consumption among Chinese children and adolescents remains relatively low.Higher consumption was inversely associated with BFP in children aged 6–17 years.Future interventional studies should assess how increased coarse cereals consumption prevents childhood obesity.
基金supported by the National Natural Science Foundation of China (Nos.42022050 and 42277088)the Guangdong Basic and Applied Basic Research Fund Committee (Nos.2021A1515011248 and 2023A1515012010)the Guangdong Foundation for the Program of Science and Technology Research (No.2020B1212060053).
文摘Thermodynamic modeling is still themostwidely usedmethod to characterize aerosol acidity,a critical physicochemical property of atmospheric aerosols.However,it remains unclear whether gas-aerosol partitioning should be incorporated when thermodynamicmodels are employed to estimate the acidity of coarse particles.In this work,field measurements were conducted at a coastal city in northern China across three seasons,and covered wide ranges of temperature,relative humidity and NH_(3) concentrations.We examined the performance of different modes of ISORROPIA-II(a widely used aerosol thermodynamic model)in estimating aerosol acidity of coarse and fine particles.The M0 mode,which incorporates gas-phase data and runs the model in the forward mode,provided reasonable estimation of aerosol acidity for coarse and fine particles.Compared to M0,the M1 mode,which runs the model in the forward mode but does not include gas-phase data,may capture the general trend of aerosol acidity but underestimates pH for both coarse and fine particles;M2,which runs the model in the reverse mode,results in large errors in estimated aerosol pH for both coarse and fine particles and should not be used for aerosol acidity calculations.However,M1 significantly underestimates liquid water contents for both fine and coarse particles,while M2 provides reliable estimation of liquid water contents.In summary,our work highlights the importance of incorporating gas-aerosol partitioning when estimating coarse particle acidity,and thus may help improve our understanding of acidity of coarse particles.
基金supported by the National Natural Science Foundation of China(Nos.42007325 and 42177211).
文摘To understand the differences in the composition and sources of PM_(2.5) and PM_(10) caused by coarse particles,integrated PM_(2.5) and PM_(10) samples were synchronously collected in Nanjing,East China,in summer 2020 and winter 2020/2021.Bulk and molecular speciation and light absorption measurements of aerosol extractswere performed,followed by positivematrix factorization(PMF)based on the PM_(2.5) and PM_(10) data sets,respectively.The difference in average concentrations of total bulk species between PM_(2.5) and PM_(10) was mainly caused by the distribution of considerable NO_(3)^(–),SO42–,Ca^(2+),and organic carbon(OC)in coarse particles.Coarse PMinfluenced by abrasion products from tirewear and leaves contributed about half of the low-volatility n-alkanes in summer.The contribution of coarse PM to biomass burning tracers and water-soluble OC increased in winter when biomass combustion was excessively active.More than 70%of sugar polyols were attributable to coarse PM in summer,and biomass burning could be an important source in winter.The light-absorbing organic chromophores were almost entirely associated with PM_(2.5),but water-soluble organic carbon(WSOC)exhibited stronger light absorption in PM_(10) extracts than in PM_(2.5) extracts possibly due to the influence of coarse PMon pH.PMF analysis indicated that biomass burning,aqueous-phase reactions,and processed dust were the main contributors of organic matter and its light absorption in winter.Biogenic primary and secondary sources made discernable contributions only in summer.The differences between PM_(2.5) and PM_(10) were likely attributed to mixing of crustal dust,combustion particles,and surface reactions.
基金supported by the National Key Research and Development Program of China(No.2022YFB3706901)the National Natural Science Foundation of China(No.52274382。
文摘The complex grain fragmentation mechanisms of coarse grains in titanium alloys under multi-directional forging(MDF)directly influence the optimization and control of primary hot working processes.This study conducted MDF experiments onβ-phase as-cast Ti-6554 alloy and simulated non-uniform deformation during cyclic multi-directional compression through macro-and micro-deformation modeling.The results revealed that friction and surface cooling caused low strain and tensile stress concentration at billet edges,leading to mixed grain structures.In contrast,high strain and triaxial compressive stress at billet centers facilitated uniform grain refinement.After 14 compressions and 4 intermediate reheating processes,coarse grains of the billet were refined from 2-5 mm to 0.25-0.50 mm,achieving uniform grain sizes across different regions.For the first time,the orientation evolution of grains with different morphologies during multi-directional compressions was visualized microscopically.Columnar grains were found to be more easily subdivided than equiaxed grains due to local strain accumulation.Under cumulative compressions,grain orientations gradually rotated from uniform to random,driving continuous dynamic recrystallization(CDRX).Slip system interactions and concentrated misorientation led to the formation and extension of transition and shear bands,inducing grain fragmentation dominated by transgranular subdivided CDRX.Smooth grain boundaries transformed into serrated ones after multiple passes,providing additional nucleation sites for discontinuous dynamic recrystallization(DDRX)and facilitating boundary expand CDRX.The interaction of diverse DRX mechanisms was the fundamental cause of grain refinement.This study clarified the principles of refining and homogenizing millimeter-grade coarse grains under increasing forging strain,offering valuable insights for the development of primary hot processing techniques for as-castβtitanium alloys.
基金Project(2021GK1040) supported by the Major Projects of Scientific and Technology Innovation of Hunan Province,ChinaProjects(52375398,52171018) supported by the National Natural Science Foundation of China+1 种基金Project(Kfkt2023-09) supported by the Open Research Fund of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,ChinaProject(E2021203059) supported by the Natural Science Foundation of Hebei Province,China。
文摘This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.
基金supported by“the Fundamental Research Funds for the Central Universities”,North Minzu University(2022XYZHG07).
文摘This work investigates the influence of carbon residue on the crystallization and solidification behavior of slag at different temperatures and cooling methods as it has a significant impact on the flow and discharge of slag,as well as the proper functioning of gasification equipment.The experimental approach involves the utilization of various techniques,namely ash fusion temperature(AFT)tests,X-ray fluorescence spectroscopy,X-ray diffraction(XRD),scanning electron microscopy(SEM),differential thermal analysis(DSC),and K-value semiquantitative analysis.The results obtained from ash fusion temperature(AFT)tests indicate that the coarse slag exhibits a relatively higher flow temperature compared to the decarburized coarse slag.XRD analysis reveals the presence of diffraction peaks corresponding to Fe and Fe3Si when residue carbon is present in the slag.In contrast,no such peaks are observed in the decarburized coarse slag subjected to the same temperature and cooling mode.This implying that the carbothermal reaction affects the slag's crystallization behavior,consequently influencing the flow temperature in the presence of residual carbon.SEM analysis illustrates that the spheroidization phenomenon is obvious when there is residual carbon in the coarse slag,but there is no spheroidization phenomenon in the decarburized coarse slag.This shows that the surface tension of slag is affected by the presence of residual carbon.Furthermore,DSC results confirm the crystallization transformation and mineral decomposition of the slag at high temperatures.For both carbon-containing slag and decarburized coarse slag,the content of crystals obtained under quenching condition is obviously lower than that under natural cooling condition.
基金fnancially supported by the Czech Science Foundation(P504/23-05132S)by the Masaryk University Institutional Grant for Doctoral Students(MUNI/A/1667/2024).
文摘Coarse woody debris(CWD) plays a crucial role in maintaining biodiversity in forest ecosystems by supporting habitat complexity and influencing soil properties.This study investigates the effects of CWD on gastropod diversity within managed spruce(Picea abies) forests in the Czech Republic,comparing results to nearby nature reserves(NRs).Gastropod species richness and composition were evaluated at both plot(50 m×50 m) and mesohabitat scales across gradients of CWD and beech(Fagus sylvatica) tree representation.Our results indicate significantly reduced species richness in managed forests(median 7 species per plot) compared to NRs(median15 species),attributed to lower soil pH,calcium availability,and moisture due to the dominance of spruce and the limited availability of CWD.Species richness was positively influenced by CWD volume,with two amounts identified:a minimum of 4 m^(3)·ha^(-1) to prevent significant biodiversity loss and 20 m^(3)·ha^(-1)to support sensitive and dendrophile species.At the within-plot scale,CWD was the species richest mesohabitat,playing a particularly important role in acidic and nutrient-poor environments.Furthermore,beech basal area positively correlated with species richness,mitigating the negative impact of spruce.The findings highlight the critical need for changes in forest management,including increased retention of CWD and integration of deciduous trees,to support biodiversity in intensively managed forests.These measures are particularly urgent given the susceptibility of spruce monocultures to climate change and pest outbreaks.Gastropods,as sessile indicators of environmental change,may serve as effective umbrella species for conservation efforts targeting forest soil biodiversity.
基金Funded by the Scientific Research Program of Jilin Provincial Department of Education(No.JJKH20250981KJ)。
文摘CGCS(coal gasification coarse slag)and desert sand composite aggregate replacing river sand for the preparation of concrete(coal gasification coarse slag and desert sand composite fine aggregate concrete,abbreviated as CDFC)were investigated to study the effect of different CGCS dosages,the sand rate of concrete,and the dosage of fly ash(FA)in cementitious material on the mechanical properties of the concrete and the excessive zone at the aggregate interface.The experimental results show that,with the increase of CGCS admixture,the CDFC water-cement ratio decreases,and the strength shows first increase and then decrease;with the increase of concrete sand rate,the CDFC strength shows first increase and then decrease,and with the increase of FA,the CDFC strength shows first increase and then decrease,when the dosage of cementitious material is 360 kg/m^(3),the composite fine aggregate dosage is 872 kg/m^(3),and the coarse aggregate dosage is 983 kg/m^(3),the maximum compressive strength of its CGCS is 47.4 MPa.The microstructures of CGCS and hydration products were analyzed by X-ray fluorescence spectrometry(XRF),X-ray diffraction(XRD),Fourier transform infrared spectrometry(FTIR),and scanning electron microscopy(SEM).It is found that the CDFC as fine aggregate can generate hydration products such as hydrated calcium silicate gel(C-S-H)in the transition zone of the concrete interface,which can greatly improve the weak zones of the concrete,and improve the strength.
基金supported by the National Key Research and Development Program of China(Nos.2022YFB3706901,2022YFB3706903)the National Natural Science Foundation of China(No.52274382)。
文摘Hot compression experiments were conducted under conditions of deformation temperatures ranging from 950 to 1150℃,strain rates of 0.001-10 s^(-1),and deformation degrees ranging from 20%to 80%.The hot deformation behavior and microstructure evolution of millimeter-grade coarse grains(MCGs)in the as-cast Ti-6Cr-5Mo-5V-4Al(Ti-6554)alloy were studied,and a hot processing map was established.Under compression along the rolling direction(RD),continuous dynamic recrystallization(CDRX)ensues due to the progressive rotation of subgrains within the MCGs.Along the transverse direction(TD),discontinuous dynamic recrystallization(DDRX)resulting from grain boundary bulging or bridging,occurs on the boundaries of the MCGs.With decreasing strain rate,increasing temperature,and higher deformation degree,dynamic recrystallization becomes more pronounced,resulting in a reduction in the original average grain size.The optimal processing parameters fall within a temperature range of 1050-1150℃,a strain rate of 0.01 s^(-1),and a deformation degree between 40%and 60%.
基金Projects(52275388,52075474)supported by the National Natural Science Foundation of ChinaProject(236Z1008G)supported by the Special Project of Hebei Provincial Central Government Guiding Local Science and Technology Development,China+1 种基金Project(E2022203206)supported by the Natural Science Foundation of Hebei Province,ChinaProject(241080457A)supported by the Shijiazhuang's University-Industry-Academia Cooperation Project in Hebei Province-Major Science and Technology Special Project,China。
文摘After the hot deformation sample of Ti-10V-2Fe-3Al alloy was treated by solid solution in theα+βtwo-phase region,the coarseβgrains that often appeared in theβsingle phase region were observed in the local region,indicating that the abnormal grain growth occurred in the local microstructural region,and the macrostructure also showed abnormally coarse grains(ACGs).The dynamic recrystallization(DRX)behavior of Ti-10V-2Fe-3Al titanium alloy was systematically investigated through hot compression tests on the Gleeble-3800 system.The DRX model ofβgrains was established,and the quantitative correlation between DRX characteristics and the appearance of ACG was clarified.Based on these results,a numerical simulation platform was developed to realize the visual prediction of ACG distribution.The results show that the increase of deformation temperature and the decrease of strain rate both contribute to a significant increase in the grain size(d_(DRX)))and volume fraction(X_(DRX))of DRXed grains.However,the proper X_(DRX)and smaller d_(DRX))at low deformation temperature and high strain rate make the macro and microstructure show ACGs after solid solution.Interestingly,if the DRX degree is excessive or insufficient,ACGs cannot be produced,indicating that ACGs are solid solution products based on the appropriate DRX degree.According to the flow curves and statistical results of microstructure,the quantitative model of DRX kinetics and DRX grain size model were constructed,and the quantitative criterion model that is related to the formation of ACG with grain size(d_(DRX)))and volume fraction(X_(DRX))of DRXed grains as the key parameters was established,i.e.,d_(DRX)≤2.60µm,72.5%≤X_(DRX)≤87.9%.By integrating the subroutine of coarse grain criterion,the isothermal compression process of cylindrical samples and the actual die forging process of H-shaped parts were simulated by DEFORM-3D software of finite element(FE),respectively,and the visual prediction of the distribution of macroscopic ACGs was realized.There is a good consistency between the tested results and the simulated results,indicating a strong correlation between macroscopic ACGs and microscopic DRX.
基金Project(2013zzts025)supported by the Fundamental Research Funds for the Central Universities of China
文摘Coarse grained WC-9Co cemented carbides with 0-1.0% TaC(mass fraction) were fabricated by HIP-sintering and gas quenching. The effects of TaC on the microstructures and mechanical properties were investigated using scanning electron microscopy(SEM), energy dispersive X-ray analysis(EDS), X-ray diffractometry(XRD) and mechanical properties tests. The results show that the maximum values of hardness and strength are HV 1124 and 2466 MPa respectively when 0.4% TaC is added. When the content of TaC is more than 0.6%, the grain size of WC is no longer affected by the amount of TaC, and(W,Ta)C occurs as well. Moreover, the strength and fracture toughness increase and the(Ta+W) content decreases with the increase of TaC content. The dependence of(Ta+W) content on the mechanical properties indicates that(Ta+W) content in Co should be decreased as low as possible to improve the mechanical properties of coarse grained WC-TaC-9Co cemented carbides with the microstructure of WC+γ two phase regions.
基金Project (51005112) supported by the National Natural Science Foundation of ChinaProject (2010ZF56019) supported by the Aviation Science Foundation of China+1 种基金Project (GJJ11156) supported by the Education Commission of Jiangxi Province, ChinaProject(GF200901008) supported by the Open Fund of National Defense Key Disciplines Laboratory of Light Alloy Processing Science and Technology, China
文摘The high temperature deformation behaviors of α＋β type titanium alloy TC11 （Ti-6.5Al-3.5Mo-1.5Zr-0.3Si） with coarse lamellar starting microstructure were investigated based on the hot compression tests in the temperature range of 950-1100 ℃ and the strain rate range of 0.001-10 s-1. The processing maps at different strains were then constructed based on the dynamic materials model, and the hot compression process parameters and deformation mechanism were optimized and analyzed, respectively. The results show that the processing maps exhibit two domains with a high efficiency of power dissipation and a flow instability domain with a less efficiency of power dissipation. The types of domains were characterized by convergence and divergence of the efficiency of power dissipation, respectively. The convergent domain in a＋fl phase field is at the temperature of 950-990 ℃ and the strain rate of 0.001-0.01 s^-1, which correspond to a better hot compression process window of α＋β phase field. The peak of efficiency of power dissipation in α＋β phase field is at 950 ℃ and 0.001 s 1, which correspond to the best hot compression process parameters of α＋β phase field. The convergent domain in β phase field is at the temperature of 1020-1080 ℃ and the strain rate of 0.001-0.1 s^-l, which correspond to a better hot compression process window of β phase field. The peak of efficiency of power dissipation in ℃ phase field occurs at 1050 ℃ over the strain rates from 0.001 s^-1 to 0.01 s^-1, which correspond to the best hot compression process parameters of ,8 phase field. The divergence domain occurs at the strain rates above 0.5 s^-1 and in all the tested temperature range, which correspond to flow instability that is manifested as flow localization and indicated by the flow softening phenomenon in stress-- strain curves. The deformation mechanisms of the optimized hot compression process windows in a＋β and β phase fields are identified to be spheroidizing and dynamic recrystallizing controlled by self-diffusion mechanism, respectively. The microstructure observation of the deformed specimens in different domains matches very well with the optimized results.
基金The National Natural Science Foundation of China(No.51108081)
文摘To investigate migration and evolution rules of coarse aggregates in the static compaction process, an algorithm of generating digital coarse aggregates that can reflect real morphology（ such as shape, size and fracture surface） of aggregate particles, is represented by polyhedral particles based on the discrete element method（ DEM）. A digital specimen comprised of aggregates and air voids is developed. In addition,a static compaction model consisting of a digital specimen and three plates is constructed and a series of evaluation indices such as mean contact force σMCF, wall stress in direction of zcoordinate σWSZZ, porosity and coordination numbers are presented to investigate the motion rules of coarse aggregates at different compaction displacements of 7. 5, 15 and 30 mm. The three-dimensional static compaction model is also verified with laboratory measurements. The results indicate that the compaction displacements are positively related to σMCF and σWSZZ, which increase gradually with the increase in iterative steps. When the compaction proceeds, the digital specimen porosity decreases, but the coordination number increases. The variation ranges of these four indices are different at different compaction displacements. This study provides a method to analyze the compaction mechanism of particle materials such as asphalt mixture and graded broken stone.
文摘Quartz, the second most abundant mineral in the earth's crust, is a gangue mineral in practically every flotation process. Coarse quartz flotation has been a long standing problem in various mineral processing plants to reduce milling cost and increase valuable mineral recovery. Based on this, the effects of nanobubbles(NBs) and hydrodynamic parameters on coarse quartz particle flotation were systematically investigated. Mechanical flotation experiments were carried out using the 7 cm and 9 cm diameter impellers in order to produce different hydrodynamic conditions. 900–1300 rpm impeller speeds were used for the 7 cm diameter impeller and 554–786 rpm for the 9 cm diameter impeller. The results show that the presence of NBs increased the flotation recovery of à425 + 106 lm quartz by up to 21%. For the7 cm diameter impeller, the maximum flotation recoveries of 86.4% and 98% were obtained in the absence and presence of NBs at Reynolds number(Re) of 81,000 and 66,000, respectively. For the 9 cm diameter impeller, the maximum recoveries of 86.3% and 97.5% were obtained in the absence and presence of NBs at Re of 90,000 and 75,000, respectively. NBs increased the flotation rate constant up to 36%.
文摘A new coarse tuning loop for a wide-band dual-loop frequency synthesizer is presented. The coarse tuning structure is composed of two digital modules, including a successive approximation register and a frequency comparator with a novel structure. The frequency comparator counts the prescaler cycles within a certain reference time and compares the number with preset data to estimate the VCO frequency. The frequency comparison error is analyzed in detail. Within a given coarse tuning time,our proposed structure shows a comparison error 20 times smaller than that of other reported structures. This structure also reuses the programmable divider as a part of the coarse tuning loop so that the circuit is greatly simplified.
基金Project(51722401)supported by the National Science Foundation for Excellent Young Scholars of ChinaProject(51334001)supported by the Key Program of National Natural Science Foundation of ChinaProject(FRF-TP-18-003C1)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Adding polypropylene(PP)fibers and coarse aggregates has become a popular way to enhance the strength and stability of the cemented tailings backfilling(CTB)body.It is essential to explore the influence of tailings-aggregate ratio and fiber content on the mechanical properties of CTB samples.The comprehensive tests of the unconfined compressive strength(UCS),slump and microstructure were designed,and the regression models were established to characterize the effect of the strength,ductility and fluidity.The results indicate that the tailings-aggregate ratio of 5:5 and PP fiber content of 0.5 kg/m^(3) are the optimum point considering the UCS,cracking strain,peak strain and post-peak ductility.The tailings-aggregate ratio is consistent with the unary quadratic to the UCS and a linear model with a negative slope to the slump.Microstructural analysis indicates that PP fiber tends to bridge the cracks and rod-mill sand to serve as the skeleton of the paste matrix,which can enhance the compactness and improve the ductility of the CTB.The results presented here are of great significance to the understanding and application of coarse aggregates and fibers to improve the mechanical properties of CTB.
文摘The influence of Nb on microstructure, mechanical property and the transformation kinetics of the coarse grain heat affected zone （CGHAZ） in HSLA steels for different heat inputs, has been investigated. When welded at higher heat inputs （100-60 kJ/cm）, impact toughness values of the steel without Nb are much higher than those of the steel with Nb, and the lowest span is 153 J at 60 kJ/cm. But only a little higher values are observed at lower heat inputs （40-30 kJ/cm）, and the highest span is 68 J at 30 kJ/cm. Dilatation studies indicate that continuous cooling transformation starting temperatures （Ts） of CGHAZ for the steel with Nb are approximately 15-30℃ which are lower than those of the steel without Nb at all heat inputs. For higher heat inputs, Nb in solid solution suppresses ferrite transformation and promotes the formation of granular bainite which has detrimental effect on impact toughness. For lower heat inputs higher Charpy impact energy values in the steel with Nb are associated with the formation of low carbon self-tempered martensite.
基金Funded by the National Mega-project of Scientific & Technical Supporting Programs,Ministry of Science & Technology of China(No.2006BAJ04A04)the Education Department of Liaoning Province,China(No. 2008282)
文摘The influence of coarse aggregate content on concrete properties was investigated.From the perspective of Frame Concrete Theory,six groups concrete were produced with the same proportion except for coarse aggregate content,with coarse aggregate content of 0%,40%,50%,60%,75%,and 80%,respectively.Slump,compressive and flexural tensile strengths,elastic modulus,and water penetration were tested to research the effect of coarse aggregate content on concrete.The experimental results reveal that slump reduces with increasing of coarse aggregate content,while compressive strength,elastic modulus and flexural tensile strength increase with the coarse aggregate content increasing,and water penetration reduces with coarse aggregate content increasing before 75% then increased.Workability,strength,durability and economical indexes system were established to optimize the coarse aggregate content in concrete based on efficacy coefficient method.The optimization results show that when coarse aggregate content is 60%,the system efficacy coefficient reaches to 0.89,and it expresses the better comprehensive performance.
基金This work was financially supported by the National Natural Science Foundation of China （NSFC, Grant Nos. 51374260, 51504048 and 51611130062）. The authors thank the members of Laboratory of Metallurgy and Materials, Chongqing University, for the support of this work.
文摘Toughness is an important property for steels used in engineering applications. However, recent toughness testing has shown the existence of a significant fluctuation in toughness in a single rolled plate of titanium micro-alloyed steel. The underlying causes of this fluctuation were investigated by fractography, analysis of microstructure and measurement of inclusions. Coarse and distributed TiN inclusions were responsible for the toughness variation, as they tended to act as the potential cleavage initiators to form micro-cracks. From a calculation of the local fracture stress, the critical size of coarse TiN inclusions for dominating micro-crack propagation was 4.93 μm, and similarly that of ferrite grains was 36.6μm. Under current casting and thermo-mechanically controlled processing schedules, the toughness fluctuation of rolled steel plates can be primarily attributed to the fraction of coarse TiN inclusions larger than 5μm. A corresponding relationship between impact energy and the proportion of coarse TiN inclusions was established. Finally, a normalizing treatment was applied to refine the ferrite grains of rolled steel plates. Despite the presence of coarse TiN inclusions, this refinement in ferrite grains minimized the toughness fluctuation and improved the uniformity of the impact properties of the steel plates.
基金supported by the National Natural Science Foundation of China(Grant No.50639050)
文摘Coarse aggregates are the major infrastructure materials of concrete-faced rock-fill dams and are consolidated to bear upper and lateral loads.With the increase of dam height,high confining pressure and complex stress states complicate the shear behavfor of coarse aggregates,and thus impede the high dam's proper construction,operation and maintenance.An experimental program was conducted to study the shear behavior of dam coarse aggregates using a large-scale triaxial shear apparatus.Through triaxial shear tests,the strain-stress behaviors of aggregates were observed under constant confining pressures:300 kPa,600 kPa 900 kPa and 1200 kPa.Shear strengths and aggregate breakage characteristics associated with high pressure shear processes are discussed.Stress path tests were conducted to observe and analyze coarse aggregate response under complex stress states.In triaxial shear tests,it was found that peak deviator stresses increase along with confining pressures,whereas the peak principal stress ratios decrease as confining pressures increase With increasing confining pressures,the dilation decreases and the contraction eventually prevails.Initial strength parameters(Poisson's ratio and tangent modulus)show a nonlinear relationship with confining pressures when the pressures are relatively low.Shear strength parameters decrease with increasing confining pressures.The failure envelope lines are convex curves,with clear curvature under low confining pressures.Under moderate confining pressures,dilation is offset by particle breakage.Under high confining pressures,dilation disappears.
