Effect of granular shape on radial segregation in a two-dimensional drum

Granular segregation is widely observed in nature and industry.Most research has focused on segregation caused by differences in the size and density of spherical grains.However,due to the fact that grains typically have different shapes,the focus is shifting towards shape segregation.In this study,experiments are conducted by mixing cubic and spherical grains.The results indicate that spherical grains gather at the center and cubic grains are distributed around them,and the degree of segregation is low.Through experiments,a structured analysis of local regions is conducted to explain the inability to form stable segregation patterns with obviously different geometric shapes.Further,through simulations,the reasons for the central and peripheral distributions are explained by comparing velocities and the number of collisions of the grains in the flow layer.

The occurrence,inheritance,and segregation of complex genomic structural variation in synthetic Brassica napus

"Synthetic"allopolyploids recreated by interspecific hybridization play an important role in providing novel genomic variation for crop improvement.Such synthetic allopolyploids often undergo rapid genomic structural variation(SV).However,how such SV arises,is inherited and fixed,and how it affects important traits,has rarely been comprehensively and quantitively studied in advanced generation synthetic lines.A better understanding of these processes will aid breeders in knowing how to best utilize synthetic allopolyploids in breeding programs.Here,we analyzed three genetic mapping populations(735 DH lines)derived from crosses between advanced synthetic and conventional Brassica napus(rapeseed)lines,using whole-genome sequencing to determine genome composition.We observed high tolerance of large structural variants,particularly toward the telomeres,and preferential selection for balanced homoeologous exchanges(duplication/deletion events between the A and C genomes resulting in retention of gene/chromosome dosage between homoeologous chromosome pairs),including stable events involving whole chromosomes("pseudoeuploidy").Given the experimental design(all three populations shared a common parent),we were able to observe that parental SV was regularly inherited,showed genetic hitchhiking effects on segregation,and was one of the major factors inducing adjacent novel and larger SV.Surprisingly,novel SV occurred at low frequencies with no significant impacts on observed fertility and yield-related traits in the advanced generation synthetic lines.However,incorporating genome-wide SV in linkage mapping explained significantly more genetic variance for traits.Our results provide a framework for detecting and understanding the occurrence and inheritance of genomic SV in breeding programs,and support the use of synthetic parents as an important source of novel trait variation.

Effect of casting process on the inner-wall band segregation of high-strength antisulfur pipes

Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic stirring,end electromagnetic stirring,casting speed and soft reduction)for the smelting of high-strength antisulfur pipes.The microstructures of continuous-casting billets and hot-rolled or tempered pipes were analyzed using a metallographic microscope and scanning electron microscope.The mechanism and evolution law regarding the inner-wall band segregation of high-strength antisulfur pipes were studied,and the influence of different casting processes was explored.

Microstructure,segregation and precipitate evolution in directionally solidified GH4742 superalloy

The evolution of microstructure,elemental segregation,and precipitation in GH4742 superalloy under a wide range of cooling rates was investigated using zonal melting liquid metal cooling(ZMLMC) experiments.Comparing various nickel-based superalloys,the primary dendrite spacing is significantly linearly correlated with G^(-1/2)V^(-1/4) at high cooling rates,where G and V are temperature gradient and drawing rate,respectively.As the cooling rate decreases,the primary dendrite spacing increases in a dispersive manner.The secondary dendrite arm spacing is significantly correlated with(GV)^(-0.4) for all cooling rate ranges.The degree of elemental segregation increases and then decreases as the cooling rate increases,which is due to the competition between solute counter-diffusion and dendrite tip subcooling.With increasing the solidification rate,the size of γ′,carbides,and non-metallic inclusions gradually decreases.The morphology of the γ′ precipitate changes from plume-like to cubic to spherical.The morphology of carbide changes from block to fine-strip then to Chinese-script.The morphology of carbide is controlled by both dendrite interstitial shape and element diffusion.The inclusions are mainly composite inclusions,which usually show the growth of Ti(C,N) with oxide as the heterogeneous nucleation center and carbide on the outer surface of the carbonitride.As the cooling rate increases,the number density of composite inclusions first increases and then decreases,which is closely related to the elemental segregation behavior.

Atomic-scale insights of indium segregation and its suppression by GaAs insertion layer in InGaAs/AlGaAs multiple quantum wells

The In segregation and its suppression in InGaAs/AlGaAs quantum well are investigated by using high-resolution x-ray diffraction(XRD)and photoluminescence(PL),combined with the state-of-the-art aberration corrected scanning transmission electron microscopy(Cs-STEM)techniques.To facility our study,we grow two multiple quantum wells(MQWs)samples,which are almost identical except that in sample B a thin GaAs layer is inserted in each of the InGaAs well and AlGaAs barrier layer comparing to pristine InGaAs/AlGaAs MQWs(sample A).Our study indeed shows the direct evidences that In segregation occurs in the InGaAs/AlGaAs interface,and the effect of the Ga As insertion layer on suppressing the segregation of In atoms is also demonstrated on the atomic-scale.Therefore,the atomic-scale insights are provided to understand the segregation behavior of In atoms and to unravel the underlying mechanism of the effect of GaAs insertion layer on the improvement of crystallinity,interface roughness,and further an enhanced optical performance of InGaAs/AlGaAs QWs.

Experimental investigation of the mixing efficiency via intensity of segregation along axial direction of a rotating bar reactor

As a significant index to evaluate the mixing efficiency,studying the concentration distribution is directly related to the intensity of segregation(I_(s)).In this work,the I_(s) of the mixture composed of NaCl solutionwater was investigated experimentally in a rotating bar reactor(RBR)by the conductivity method.The results showed that the mixing efficiency was improved along the axial direction from the bottom to the top in the RBR.The concentration distribution at the bottom section was more uneven,and I_(s) was higher compared with the top section,which decreased from 6.53×10^(-5)to 1.57×10^(-7).With the increase of rotational speed from 0 to 700 r·min^(-1),I_s at the bottom and top sections decreased from 4.27×10^(-3)to 7.10×10^(-5)and from 1.93×10^(-3)to 7.29×10^(-7),respectively.The increases flow rate of solution A,and the decreases of concentration of NaCl and flow rate of solution B gave rise to the reduction of I_(s),signifying an improved mixing efficiency.The results revealed that the conductivity method used in this paper has high efficiency and low cost to measure the I_(s),which indicates a promising prospect for estimating reactors'mixing performance.

Stretchable alkenamides terminated Ti_(3)C_(2)T_(x)MXenes to release strain for lattice-stable mixed-halide perovskite solar cells with suppressed halide segregation

Bandgap-tunable mixed-halide perovskite materials have attracted considerable interest because of their indispensability as top counterparts in tandem solar cells.However,the soft and disordered lattice always suffers from severe phase segregation under illumination,which is particularly susceptible to residual lattice strain.Herein,we report a strain regulation strategy by using alkenamides terminated Ti_(3)C_(2)T_(x)MXenes as an additive into perovskite precursor.Apart from the role of a template for grain growth to obtain high-quality films,the stretchable alkyl chain promotes lattice shrinkage or expansion to form an elastic grain boundary to eliminate the spatially distributed stain and shut down ion migration channels.As a result,the all-inorganic perovskite solar cells based on CsPbIBr_(2)and CsPbI_(2)Br halides achieve prolonged device stability under harsh conditions and the best power conversion efficiencies up to 11.06%and 14.30%,respectively.

Moisture-Induced Non-Equilibrium Phase Segregation in Triple Cation Mixed Halide Perovskite Monitored by In Situ Characterization Techniques and Solid-State NMR

Environmental stability is a major bottleneck of perovskite solar cells.Only a handful of studies are investigating the effect of moisture on the structural degradation of the absorber.They mostly rely on ex situ experiments and on completely degraded samples,which restrict the assessment on initial and final stage.By combining in situ X-ray diffraction under controlled 85%relative humidity,and live observations of the water-induced degradation using liquid-cell transmission electron microscopy,we reveal two competitive degradation paths leading on one hand to the decomposition of state-of-theart mixed cation/anion(Cs_(0.05)(MA_(0.17)FA_(0.83))_(0.95)Pb(Br_(0.17)I_(0.83))_(3)(CsMAFA)into PbI_(2) through a dissolution/recrystallization mechanism and,on the other hand,to a non-equilibrium phase segregation leading to CsPb_(2)Br_(5) and a Cesium-poor/iodide-rich Cs_(0.05)-x(MA_(0.17)FA_(0.83))_(0.95)Pb(Br_(0.17-2y)I_(0.83)+2y)_(3) perovskite.This degradation mechanism is corroborated at atomic-scale resolution through solid-state ^(1)H and ^(133)Cs NMR analysis.Exposure to moisture leads to a film containing important heterogeneities in terms of morphology,photoluminescence intensities,and lifetimes.Our results provide new insights and consensus that complex perovskite compositions,though very performant as champion devices,are comparatively metastable,a trait that limits the chances to achieve long-term stability.

圆筒混合机内不同粒径颗粒的轴向分离研究

为了探讨颗粒在圆筒混合机的轴向分离机理,提出了一种由多段摩擦系数不同圆筒组成的新型圆筒混合机结构.以颗粒堆积角为参考,通过仿真与实验测试得到了颗粒的参数,并基于圆筒混合机分离实验验证了仿真模型.以此为基础,开展基于离散元法的不同粒度颗粒在圆筒混合机内分离过程的数值模拟研究,根据颗粒分布、休止角、运动速度、回转半径等分析了不同粒径颗粒在分离过程中的流动形态,并基于分离指数探讨颗粒的分离特性.结果表明:圆筒混合机侧壁摩擦系数不同将导致颗粒休止角不同,从而使不同区间颗粒的运动速度不同,高摩擦系数区域内颗粒运动快,而低摩擦系数区域内颗粒运动较慢;运动速度的不同导致颗粒在新型圆筒混合机内将产生明显的轴向分离现象,小粒径颗粒聚集在低摩擦系数区,而大粒径颗粒聚集在高摩擦系数区.

SPA-H钢分层缺陷问题分析及改进措施

针对SPA-H热轧板加工过程中出现的分层缺陷问题,通过宏观观察、金相分析、组织分析后认为,材料中的Al_(2)O_(3)夹杂物及偏析是导致分层缺陷的主要原因。采取了降低转炉终点氧含量、优化钢包顶渣改质工艺、全程保护浇铸、确定拉速为(1.55±0.05) m/min、确定过热度为(25±5)℃等措施后,夹杂缺陷返修率为零,材料中未发现明显偏析。

铜基偏晶合金的研究现状

铜基偏晶合金(Cu-Co、Cu-Fe、Cu-Cr等)具有优异的电、磁、力学等特性,受到国内外材料科学领域学者的广泛关注。在制备过程中,铜基偏晶合金由于发生液相分离行为并形成严重的偏析组织现象,被称为不混溶合金。过去的研究主要集中于寻求使铜基偏晶合金组织均匀的制备方法,然而近期研究表明,偏析组织异质结构的强度-韧性协同作用有利于提高材料的韧性,这为铜基偏晶合金的进一步发展提供了新思路。本文综述了目前国内外对铜基偏晶合金的液相分离和偏析组织形成机理的理论研究成果(包括液相分离组织结构演变、液相分离热力学以及第二相液滴形核生长动力学研究),归纳了目前主流的改善偏析组织方法(包括微合金化法、快速凝固法和激光成形法),阐述了铜基偏晶合金因液相分离特性产生的双相复合微观组织结构的强度-韧性协同作用,最后对铜基偏晶合金未来的研究发展方向进行了展望。

节流式燃/氧分离组合固体发动机推力性能调节数值研究

节流式燃/氧分离组合固体发动机将燃烧室分为富燃燃烧室和富氧燃烧室,采用富燃固体推进剂和富氧固体推进剂串联装填的形式,在两个燃烧室中间增加节流阀,通过调节节流阀开度实现推力调节。利用商业软件对节流式燃/氧分离组合固体发动机在节流阀流道半径不同时的工作状态进行模拟,研究节流式燃/氧分离组合固体发动机的工作特性,获得节流式燃/氧分离组合固体发动机燃气流动和掺混特征,揭示节流式燃/氧分离组合固体发动机推力调节机理以及节流阀流道半径对节流式燃/氧分离组合固体发动机燃烧效率的影响规律。研究发现:节流阀流道开度(即节流阀流道半径R)减小可增大发动机推力;随着节流阀开度的减小,节流阀出口燃气马赫数随之增大,而发动机燃烧效率却出现先增大后减小的规律,当节流阀出口燃气流动达到临界状态时发动机燃烧效率出现最大值。

基于形态学开运算的浸矿体系孔隙结构及其演化特征

立足堆浸体系的偏析分层复杂结构,结合X-ray CT无损探测、形态学开运算处理、MATLAB和OsiriX可视化软件等手段,引入颗粒间孔隙的当量孔隙尺寸、面积、数量等关键表征参量,如从二维量化和三维可视化层面揭示浸矿体系中颗粒间孔隙结构特征及其演化规律.研究发现,细颗粒夹层呈“包裹体”状且均位于粗矿石颗粒的内部,分析认为其是造成堆浸体系颗粒偏析和分层的重要致因;浸矿作用下微细颗粒迁移导致矿堆内部发生沉积压实作用,由197 mm降至180 mm以下;浸矿21 d后,矿堆上部孔隙呈增大趋势,下部孔隙率呈减小趋势,此外,纵向当量孔隙的直径由2.81 mm减小至2.18 mm,其变化趋势和程度要显著大于横向颗粒间孔隙的当量直径;对比浸矿0 d和21 d的柱浸体系三维颗粒间孔隙结构,证实了细颗粒夹层所处区域的粘结聚集以及细颗粒夹层周边区域形成溶液绕流、溶液优势流动路径.

运移距离对CO_(2)混相驱重力超覆的影响规律及表征分析

CO_(2)驱油技术具有提高原油采收率和资源化利用与封存的双重目的,已在低渗-致密油藏得到广泛应用。为明确运移距离对CO_(2)混相驱油过程中密度差引起的重力超覆程度的影响规律,分别采用室内物理模型和数值模型开展研究。实验结果表明,混相条件下,由于岩心长度减小,重力超覆的扩展空间受限,但油气混相程度的降低,导致重力超覆程度降低幅度较小;当岩心长度继续减小时,混相程度降低对重力超覆的影响大于岩心长度对重力超覆扩展空间限制的影响,从而使重力超覆程度加剧。数模结果表明,随着运移距离的减小,重力超覆程度减弱,混相驱采收率提高。因此,结合油田现场情况,为减缓重力超覆,应适当减小井距,缩短CO_(2)气体运移距离,从而提高CO_(2)驱的波及效率。研究结果对于CO_(2)驱油现场试验方案设计和参数优化具有一定的指导意义。

节流式燃/氧分离组合固体火箭发动机动态工作过程数值研究

利用商业软件ANSYS Fluent对节流式燃/氧分离组合固体火箭发动机动态工作过程进行数值研究,揭示该发动机基本动态工作过程以及节流阀作动速度的影响。结果表明,节流阀作动会导致发动机富氧燃烧室压强、节流阀出口质量流量以及发动机推力出现负调现象;节流阀作动速度差异不影响发动机调节后的稳定工作状态;随着节流阀作动速度增大,发动机达到稳定工作状态所需时间逐渐缩短,实现性能调控的响应速度增快,但发动机各参数负调量也随之增大,从而增加了发动机发生振动的风险。

250 mm×250 mm轴承钢大方坯压下工艺优化及质量提升

建立了250 mm×250 mm轴承钢大方坯的凝固传热模型,并根据凝固平方根定律验证了模型的准确性。讨论了拉速和过热度对凝固终点的影响,并制定新的压下制度。运用不同压下制度进行了工业试验,试验结果表明:优化后的压下制度基本消除大方坯的中心缩孔,使得中心偏析比由1.1降低至1.0,同时使得V形偏析线上最高碳含量由1.391%降至1.184%,V形偏析线上和非偏析线上的平均碳含量极差由0.113%降至0.07%。

潮湿细粒煤复合式干法分选特性研究

为研究潮湿细粒煤复合式干法分选效率,对潮湿细粒煤进行了振动强度和气速的单因素试验,结合RSM-BBD预测模型获得了最优参数;并探索了不同水分的原煤在不同分选时间内的分选效果,同时分析了气流对潮湿细粒煤分选过程的影响,并评价了分选效果。结果表明:随着分选时长的增加,分选效果明显提高,最大灰分离析度可达12.05。试验煤样在气速为0.78 m/s,振动频率为25 Hz,振幅为3 mm时达到最佳分选效果,此时可能偏差E=0.135 g/cm^(3),且在此条件下分选产品有很好的脱水效果,复合式干法分选可实现潮湿煤炭的提质。该研究可以对细粒煤炭的干法分选工艺提供理论和技术支持。

热轧Q460C板剪切分层原因分析

本文对剪切过程中分层的热轧20mm Q460C板进行了硫印、冷蚀低倍试验,结果显示分层部位存在硫化物的连续、条状偏析带,且偏析带对应部位已开裂。然后采用金相显微技术对硫印、酸洗试验中发现的心部分层开裂部位进行了微观观察和分析,结果显示分层开裂部位的硫化物偏析带对应的硫化物呈网状、密集状态分布,个别硫化物边缘有开裂现象,同时局部析出2~10um网状分布的氮化钛颗粒。4%硝酸酒精侵蚀后,发现网状、密集分部的硫化物、氮化钛颗粒分布于网状铁素体晶粒内,心部开裂部位组织为贝氏体+共析网状铁素体+先共析断网状铁素体,裂纹沿共析网状铁素体和网状硫化物扩展。

虾夷扇贝F_(1)自交衰退及其遗传调控机理

近交导致的种质退化严重影响虾夷扇贝养殖产业。为探明虾夷扇贝近交衰退的现象及遗传调控机理,在表型水平上,构建近交系数分别为0.5、0.25和0的自交组、近交组与自然群体对照组,追踪不同近交系数下虾夷扇贝幼虫期到成体期530日龄的性状差异,同时选取7个适合度性状,利用主成分分析法构建基于近交衰退的适合度指标评价方法;在基因组水平上,利用1个自交家系的亲本及其21个子代进行全基因组重测序,开展标记偏分离分析。试验结果显示:针对存活率性状,在幼虫期,自交组近交衰退率是近交组的1.31~3.05倍;在成体期,自交组近交衰退率是近交组的0.97~7.29倍。而生长性状,在幼虫期,仅有自交组保持较低的近交衰退率(1.65%~2.56%);在成体期,自交组与近交组几乎未发生衰退。基于重测序分型得到1253519个单核苷酸多态性用于偏分离统计,约99%在子代中发生了显著的偏分离,其中23%属于配子偏分离、77%属于合子偏分离,合子偏分离中有89%为杂合子过剩,即超显性效应起作用,仅10%受显性效应影响为纯合子缺失。试验结果表明,超显性效应及偏分离作用在虾夷扇贝F_(1)子代存活率性状的自交衰退中起主要作用,为近交衰退的机理提供更有力证据的同时,也为虾夷扇贝种质遗传改良提供了有效思路。

阳极氧化后某2A12铝合金零件表面缺陷的成因

阳极氧化后某2A12铝合金零件膜层异常发亮、存在表面缺陷。采用光学显微镜、扫描电子显微镜、能谱仪、X射线衍射仪等分析技术,研究了阳极氧化后零件膜层颜色异常,显现出线条状缺陷的原因。结果表明:该铝合金基体存在富铜偏析相和夹杂相,在阳极氧化过程中,基体中的偏析相优先溶解,杂质相不被氧化,导致阳极氧化膜不均匀,膜层局部区域出现孔洞和夹杂物。