Volume-averaged modeling of multiphase solidification with equiaxed crystal sedimentation in a steel ingot

Macrosegregation is a critical factor that limits the mechanical properties of materials.The impact of equiaxed crystal sedimentation on macrosegregation has been extensively studied,as it plays a significant role in determining the distribution of alloying elements and impurities within a material.To improve macrosegregation in steel connecting shafts,a multiphase solidification model that couples melt flow,heat transfer,microstructure evolution,and solute transport was established based on the volume-averaged Eulerian-Eulerian approach.In this model,the effects of liquid phase,equiaxed crystals,columnar dendrites,and columnar-to-equiaxed transition(CET)during solidification and evolution of microstructure can be considered simultaneously.The sedimentation of equiaxed crystals contributes to negative macrosegregation,where regions between columnar dendrites and equiaxed crystals undergo significant A-type positive macrosegregation due to the CET.Additionally,noticeable positive macrosegregation occurs in the area of final solidification in the ingot.The improvement in macrosegregation is beneficial for enhancing the mechanical properties of connecting shafts.To mitigate the thermal convection of molten steel resulting from excessive superheating,reducing the superheating during casting without employing external fields or altering the design of the ingot mold is indeed an effective approach to control macrosegregation.

La_5Mg_(95-x)Ni_x(x=5、10、15)合金的显微组织、储氢热力学和动力学性能（英文）

研究Ni含量对La_5Mg_(95-x)Ni_x(x=5、10、15)三元合金的显微组织、热力学和动力学性能的影响。采用XRD和SEM探索合金的相和组织的变化情况,采用自动Sievert设备测试合金吸放氢性能曲线和PCI曲线。研究表明,随着Ni含量的增加,合金的储氢动力学性能得到提高,但是合金的储氢容量有所下降。三种成分的合金中,La_5Mg_(80)Ni_(15)合金表现出最低的放氢活化能以及最高的吸放氢速率,其放氢活化能为57.7kJ/mol。通过测定合金PCI曲线和van’tHoff方程发现,随着Ni含量的增加,合金的热力学性能先提高后降低,其中La_5Mg_(85)Ni_(10)表现出最优异的热力学性能,其焓和熵的数值分别为-72.1 kJ/mol和-123.2J/(mol·K)。

ABCD评分系统在短暂性脑缺血发作病人早期发生脑卒中风险的预测

目的:进一步明确基于中国人群的短暂性脑缺血发作(transient ischemic attack,TIA)病人,3种ABCD评分系统预测TIA发作后7 d内发生新发脑梗死风险的临床应用价值。方法:150例TIA病人于入院48 h内采用ABCD2、ABCD3、ABCD3-Ⅰ3种评分系统,根据评分分为低危、中危及高危组;根据病人TIA发作后7 d内是否继发脑梗死分为新发脑梗死组和非脑梗死组,比较2组TIA病人的3种评分系统评分;记录3种评分的低、中、高危组中TIA后7 d内继发脑梗死病人例数。结果:与非脑梗死组比较,新发脑梗死组的3种不同的ABCD系统的评分结果均升高,差异具有统计学意义(P<0.05～P<0.01);除ABCD2评分外,随着ABCD3、ABCD3-Ⅰ评分分值的升高,7 d内继发脑梗死率不断增加(P<0.01);ROC曲线分析发现,3种ABCD评分系统对7 d内继发脑梗死的预测AUC分别为0.67、0.84和0.91,均大于基准线面积的0.5,差异有统计学意义(P<0.01)。ABCD3-Ⅰ预测7 d内继发脑梗死准确度优于ABCD3,ABCD3优于ABCD2,差异具有统计学意义(P<0.01)。结论:3种ABCD评分方法均能预测TIA后7 d内继发的新发脑梗死,分值越高,7 d内继发新发脑梗死的危险度越高,ABCD3-Ⅰ预测准确度最高。

Hybrid Dextran-gadolinium Nano-suitcases as High-relaxivity MRI Contrast Agents

Dextran-poly（glycidyl methacrylate） （Dex-PGMA） nano-suitcases were synthesized efficiently via a graft copolymerization induced self-assembly （GISA） approach. On this basis, the Dex-PGMA nano-suitcases were modified with hydrazide, and the attachment of multiple chelated Gd（III） ions to the interior of the nano-suitcases affords nanoscale MRI contrast agents with high relaxivity values. The highly fenestrated dextran shell of the nano-suitcases assures water exchange which readily occurs between the surrounding environment and the Gd（III） ions encapsulated within the hybrid nano-suitcases. The complexation between the hydrophilic hydrazide interior of the nano-suitcases and Gd（III） ions results in an impressive Gd payload at 22.6 wt% in the hybrid nano-suitcases. The longitudinal relaxivity （rl） of the hybrid nano-suitcases is reported as 44.4 L/（mmol-s）, which is 9-14 folds of that of commercial Gd-DTPA agents. In vivo MRI studies demonstrate that the hybrid nano-suitcases accumulated in the lymph node of the rat due to their nanoscale dimensions and displayed strong signals in vivo. The results indicated that the hybrid nano-suitcases provide a promising platform for the diagnosis of lymph node related diseases.

Gossypol detoxification in the rumen and Helicoverpa armigera larvae:A review

Gossypol,a phenolic compound found in the cotton plant,is widely distributed in cottonseed byproducts.Although ruminant animals are believed to be more tolerant of gossypol toxicity than monogastric animals due to rumen microbial fermentation,the actual mechanisms of detoxification remain unclear.In contrast,the metabolic detoxification of gossypol by Helicoverpa armigera(Lepidoptera:Noctuidae)larvae has achieved great advances.The present review discusses the clinical signs of go ssypol in ruminant animals,as well as summarizing advances in the study of gossypol detoxification in the rumen.It also examines the regulatory roles of several key enzymes in gossypol detoxification and transformation known in H.armigera.With the rapid development of modern molecular biotechnology and-omics technology strategies,evidence increasingly indicates that research into the biological degradation of gossypol in H.armigera larvae and some microbes,in terms of these key enzymes,could provide scientific insights that would underpin future work on microbial gossypol detoxification in the rumen,with the ultimate aim of further alleviating gossypol toxicity in ruminant animals.

Effects of Ni Content and Ball Milling Time on the Hydrogen Storage Thermodynamics and Kinetics Performances of La–Mg–Ni Ternary Alloys

The eifects of Ni content and ball milling time on the hydrogen storage thermodynamics and kinetics performances of asmilled La5Mg95-xNix(x=5,10,15)ternary alloys have been investigated.The evolution of microstructure and phase of experimental alloys in the absorption/desorption process has been characterized by XRD,SEM and HRTEM.The hydrogen storage kinetics and thermodynamics performances and PCI curves have been tested using the Sievert apparatus.It is found that the rising of Ni content remarkably improves the hydrogen storage kinetic performance,but reduces hydrogen storage capacity.And with the increase in milling time,hydrogen desorption activation(Ea)value decreases firstly and then increases;the minimum value is 47.6 kJ/mol,and the corresponding milling time is 10 h for La5Mg85Ni10 alloy.As for the thermodynamics properties,the hydrogenation enthalpy(△H)and hydrogenation entropy(△S)both decrease firstly and then increase with the rising of Ni content and milling time.The composite La5Mg85Ni10 alloy milled for 10 h exhibits the best thermodynamics and kinetics performances,the lowest Ea of 47.6 kJ/mol,absorption of 5.4 wt.%within 5 min and desorption of 5.2 wt.%within 3 min at 360℃and the lowest△H and△S of 72.1 kJ/mol and 123.2 J/mol/K.

由自组装构筑蛋白酶响应性近红外/磁共振双显影微球

由分子侧链上修饰近红外荧光分子的聚赖氨酸及表面聚丙烯酸修饰的磁共振显影磁性纳米颗粒为组装单元,采用自组装法构筑了在近红外、磁共振双重显影中均具有蛋白酶响应性的纳米尺度自组装微球.微球形成的组装驱动力为聚赖氨酸侧链氨基与磁性纳米颗粒表面羧基在水相中的静电相互作用,两类组装前驱体在静电力作用下组装为纳米尺度团聚体,再通过戊二醛对氨基的适度交联来构筑胰蛋白酶响应的双显影复合微球.该复合微球处于自组装聚集状态时,微球内近红外荧光分子间的距离减小从而发生荧光共振能量转移,导致荧光分子的自淬灭;而在胰蛋白酶活化后的解组装状态,微球内聚赖氨酸重复单元间的酰胺键被胰蛋白酶切断,荧光分子间距扩大,共振能量转移现象消失,从而导致复合微球在胰蛋白酶存在下释放荧光,荧光释放强度/淬灭强度的比值最高可达18.此外,自组装微球的磁共振显影同样具有胰蛋白酶敏感性,这与组装—解组装过程导致微球内磁性纳米颗粒的局部浓度及聚集状态发生变化有关.细胞和动物实验研究表明,复合微球呈现低细胞毒性,并可特异性地对胰蛋白酶阳性的细胞和组织进行近红外/磁共振双显影,在胰蛋白酶的生物影像学检测中具有潜在的应用前景.

Ultrasonographic Characteristics of Cortical Sulcus Development in the Human Fetus between 18 and 41 Weeks of Gestation

Background： Fetal brain development is a complicated process that continues throughout pregnancy. Fetal sulcus development has typical morphological features. Assessment of fetal sulcus development to understand the cortical maturation and development by prenatal ultrasound has become widespread. This study aimed to explore a reliable method to assess cortical sulcus and to describe the normal sonographic features of cortical sulcus development in the human fetus between 18 and 41 weeks of gestation. Methods： A cross-sectional study was designed to examine the fetal cortical sulcus development at 18-41 weeks of gestation. Ultrasound was used to examine the insula, sylvian fissure （SF）, parieto-occipital fissure （POF）, and calcarine fissure （CF）. Bland-Altman plots were used for assessing the concordance, and the intraclass correlation coefficient was used for assessing the reliability. Results： SF images were successfully obtained in 100% of participants at 22 weeks of gestation, while the POF images and CF images could be obtained in 100% at 23 weeks of gestation and 24 weeks of gestation, respectively. The SF width, temporal lobe depth, POF depth, and the CF depth increased with the developed gestation. The width of uncovered insula and the POF angle decreased with the developed gestation. By 23 weeks of gestation, the insula was beginning to be covered. Moreover, it completed at 35 weeks of gestation. The intra- and inter-observer agreements showed consistent reproducibility. Conclusions： This study defined standard views of the fetal sulcus as well as the normal reference ranges of these sulcus measurements between 18 and 41 weeks of gestation. Such ultrasonographic measurements could be used to identil fetuses at risk of fetal neurological structural disorders.

Optimization of flow uniformity control device for six-stream continuous casting tundish

For a multistream tundish,the uniformity among the streams plays a significant role in the quality of molten steel.How to analyze the uniformity quantitatively and optimize structures of a multistream tundish is an important research content for a multistream tundish.A new approach was proposed to quantify the uniformity among the streams.And a physical study and a numerical study were carried out to optimize the structure of the diversion hole based on the prototype of a six-stream tundish in a steel plant.On the basis of average residence time,the uniformity of each flow was considered fully and then the optimal structure of the diversion hole was obtained by means of the comprehensive analysis of temperature field and velocity field.The results show that the optimum structural parameters adopted for diversion holes are height of 20 mm,angle of 15°and diameter of 80 mm.

Interface Analysis and Hot Deformation Behaviour of a Novel Laminated Composite with High-Cr Cast Iron and Low Carbon Steel Prepared by Hot Compression Bonding

A hot compression bonding process was developed to prepare a novel laminated composite consisting of high-Cr cast iron （HCCI） as the inner layer and low carbon steel （LCS） as the outer layers on a Gleeble 3500 ther- momechanicat simulator at a temperature of 950 ℃ and a strain rate of 0. 001 s 1. Interfacial bond quality and hot deformation behaviour of the laminate were studied by mierostructural characterisation and mechanical tests. Experi- mental results show that the metallurgical bond between the constituent metals was achieved under the proposed bonding conditions without discernible defects and the formation of interlayer or intermetallic layer along the inter- face. The interfacial bond quality is excellent since no deterioration occurred around the interface which was deformed by Vickers indentation and compression test at room temperature with parallel loading to the interface. After well cladding by the LCS, the brittle HCCI can be severely deformed （about 57 % of reduction） at high temperature with crack-free. This significant improvement should be attributed to the decrease of crack sensitivity due to stress relief by soft claddings and enhanced flow property of the HCCI by simultaneous deformation with the LCS.

Characterization and Thermodynamics of Al_2O_3-MnO-SiO_2(-MnS)Inclusion Formation in Carbon Steel Billet

A method to extract inclusion particles from solid steel by electrolysis with organic electrolyte solution was introduced; meanwhile, thermodynamics of inclusion formation was calculated using FaetSage software. The results showed that there were two kinds of inclusions in the billet, i.e. Al2O3-MnO-SiO2-MnS （AMS-MnS） and Al2O3- MnO-SiO2 （AMS）. Most of AMS-MnS inclusion particles, with diameter of 10--30 μm, showed three-layer structures： SiO2-rich core with a small quantity of Mn, intermediate AMS layer, and MnS outer layer containing small quanti- ties of A1 and O. Most AMS inclusion particles were 50--90 μm and exhibited homogeneous composition. Thermo- dynamic results indicated that SiO2-rich core could form firstly by Si reacting with O in molten steel at temperatures above 1 923 K during Si-Fe alloy addition, and then, the SiO2-rich core could react with Mn and Al to form liquid AMS enveloping the SiO2 rich core at 1823- 1873 K. MnS began to precipitate from AMS when temperature reached 1 728 K. Liquid AMS could form by coupled reaction among Si, Mn, Al and O in molten steel.

A Multi-step Thermodynamic Model for Alumina Formation during Aluminum Deoxidation in Fe–O–Al Melt

Based on the two-step nucleation mechanism, a multi-step thermodynamic model for alumina inclusion for- mation during aluminum deoxidation process was proposed in Fe-O-Al melt. Thermodynamic properties of metastable intermediates including （Al2O3）n clusters for prenucleation and α-Al2O3 nanoparticle for growth process were calculated using density functional theory. Furthermore, Gibbs free energy change of forming the intermediate by reaction between the dissolved aluminum （Al） and oxygen （O） in the melt was calculated. The results indicated that the thermodynamics of （Al2O3）n at steelmaking temperature are dependent on their structures, while that of α-Al2O3 nanoparticle are dependent on their size. The nuclei of α-Al2O3 which was originated from （Al2O3）n aggregated under a high supersaturation ratio of Al and O（Rs） in the melt. There existing excess oxygen because of the low Rs, but the secondary inclusions will be formed during the cooling process due to the excess oxygen. The nuclei lager than 20 nm can grow up spontaneously and instantaneously into primary inclusions because of thermodynamic drive. It is difficult to control the size of α-Al2O3 to be less than 20 nm, in the aluminum deoxidation process of the current conditions of steelmaking.