Migration behavior of solidification nuclei in pure Al melt under effect of electric current pulse

A mathematical model considering free nuclei was developed to reveal the migration behavior of the free nuclei. Numerical simulation results show that most of the nuclei on the top surface of the melt move downwards and distribute randomly inside the Al melt, which induces more nucleation sites resulting in grain refinement. At the same time, the effect of nuclei size on the nuclei distribution and refinement employing electric current pulse （ECP） was also investigated. The smaller nuclei migrate a short distance with the Al melt at lower speed. But for the larger nuclei, the migration downwards with higher speed benefits the refinement of interior grains of the melt. The research results help to better understand the refinement process and provide a more reasonable explanation of the grain refinement mechanism using ECP.

Migration behavior, separation and recycling of rare earth during thermal decomposition of Zhijin phosphorus ore

Zhijin phosphorus ore is a moderate and low-grade phosphorus rare-earth ore contained in mines. The separation and extraction of associated rare earth are important research topics. In this study, the migration behavior of rare earth during the thermal decomposition of Zhijin phosphorus ore and the separation and extraction of rare earth in phosphorus slag are discussed systematically. During the thermal decomposition process of phosphorus ore, almost all of the associated rare earth enters into the phosphorus slag phase but does not enter into the ferrophosphorus or gas phases. Amorphous calcium metasilicate and calcium fluosilicate are major components of phosphorus slag, and rare earth mainly exists as a calsil solid solution. Hydrochloric acid was used for acidolysis of the phosphorous slag. Under the following conditions, 96% of the rare earth in the phosphorous slag can be dissolved in the acidolysis solution： acid excess coefficient of 1.5, reaction time of 50 min and reaction temperature of 50℃. The rare earth in the acidolysis solution was separated and recycled using oxalic acid as a precipitator and NaOH as a pH modifier. At pH of 1.7, rare-earth-enriched matter with rare-earth content of 2.1 wt% was obtained, and the recovery of the rare earth was 88%.

Relationship between Migration and HIV Risky Behavior: a Comparative Study of Returning Migrants and Non Migrants Based on Rural Out-of-school Youth in Jilin, China

Objective To estimate the relationship between migration and HIV risky behavior when controlling for gender, age, and educational levels and to evaluate the gender differences in migration, HIV knowledge, and HIV risky behaviors among rural youth in China. Methods A cross-sectional, anonymous, investigative questionnaire for 1710 unmarried, out-of-school rural youth, aged between 15 and 24 years, was handed out in Gongzhuling county of Jilin province, China. Results 58.5% of participants had a history of migration, irrespective of gender. There were gender differences observed in other factors such as drug abuse（4.3% for males and 5.5% for females, P〈0.01）, multiple sexual partners（24.1% for males and 44.1% for females, P〈0.01）, and HIV knowledge rate（35.2% for males and 25.5% for females, P〈0.001）. While controlling for gender, age, and educational levels, the relationships between migration and drug abuse, selling sex, and non usage of condoms during last instance of sexual activity were found to be significant. The cases of premarital sex and multiple sexual partners were both not found to be related to migration. Conclusion Among rural youth, the HIV risky behavior such as drug abuse, selling sex, and lack of condom use, is significantly related to migration, while premarital sex and multiple sexual partners seem unrelated to migration.

Effect of strain on electrochemical performance of Janus MoSSe monolayer anode material for Li-ion batteries: First-principles study

First-principles calculations are performed to investigate the effect of strain on the electrochemical performance of Janus MoSSe monolayer.The calculation focuses on the specific capacity,intercalation potential,electronic structure,and migration behavior of Li-ion under various strains by using the climbing-image nudged elastic band method.The result shows that the specific capacity is nearly unchanged under strain.But interestingly,the tensile strain can cause the intercalation potential and Li-ion migration energy barrier increase in MoSSe monolayer,whereas the compressive strain can lead to the intercalation potential and energy barrier decreasing.Thus,the rate performance of the MoSSe anode is improved.By analyzing the potential energy surface of MoSSe surface and equilibrium adsorption distance of Li-ion,we explain the physical origin of the change in the intercalation potential and migration energy barrier.The increase of MoSSe potential energy surface and the decrease of adsorption distance caused by tensile strain are the main reason that hinders Li-ion migration.

Migration mechanism of atrazine in the simulated lake icing process at different freezing temperatures based on density function theory

Atrazine causes concern due to its resistant to biodegradation and could be accumulated in aquatic organisms,causing pollution in lakes.This study measured the concentration of atrazine in ice and the water under ice through a simulated icing experiment and calculated the distribution coefficient K to characterize its migration ability in the freezing process.Furthermore,density functional theory(DFT)calculations were employed to expatiate the migration law of atrazine during icing process.According to the results,it could release more energy into the environment when atrazine staying in water phase(-15.077 kcal/mol)than staying in ice phase(-14.388 kcal/mol),therefore it was beneficial for the migration of atrazine from ice to water.This explains that during the freezing process,the concentration of atrazine in the ice was lower than that in the water.Thermodynamic calculations indicated thatwhen the temperature decreases from268 to 248 K,the internal energy contribution of the compound of atrazine and ice molecule(water cluster)decreases at the same vibrational frequency,resulting in an increase in the free energy difference of the compound from-167.946 to-165.390 kcal/mol.This demonstrated the diminished migratory capacity of atrazine.This study revealed the environmental behavior of atrazine during lake freezing,which was beneficial for the management of atrazine and other pollutants during freezing and environmental protection.

Migrating behaviors of interfacial elements and oxide layers during diffusion bonding of 6063Al alloys using Zn interlayer in air

The oxide layer on the surface has always been a key obstacle to achieving the diffusion bonding of Al alloys.It is a challenge for performing diffusion bonding without removing oxide layers.Herein,diffusion bonding of Al alloy retaining continuous oxide layers was successfully achieved in the air by a low-temperature and low-pressure diffusion bonding mothed using a Zn interlayer.During the bonding processes,conducted at 360℃ and 3 MPa,Zn diffused into Al through cracks of thin oxide layers to form the joint composed Al/(diffusion layer)/(oxide layer)/(Zn)/(oxide layer)/(diffusion layer)/Al.The diffusion layers were composed of Zn-Al eutectoid,and the oxide layer included nanocrystals and amorphous Al_(2)O_(3).The shear strength of joints containing continuous oxide layers was about 30 MPa.Interestingly,the migration behavior toward the joint center of the interfacial oxide layers was observed with consuming of the Zn interlayer.The cracking phenomenon,the“subcutaneous diffusion”and the migration behavior of oxide layers were verified and analyzed by the diffusion bonding of anodized 6063Al-6063Al.Subsequently,the dynamic migration mechanism of oxide layers with elements diffusion and bonding interface strengths were discussed in detail.The ability to join Al alloys in the air at low temperatures and low pressure suggests a highly practical and economic method for diffusion bonding.

Migration of bisphenol A and its related compounds in canned seafood and dietary exposure estimation

The present study sought to investigate the migration of target bisphenols,such as bisphenol-A(BPA),bisphenol-F(BPA),bisphenol-A diglycidyI ether(BADGE),bisphenol-A(2,3-dihydroxypropyl)glycidyl ether(BADGE.H_(2)O),bisphenol-A bis(2,3-dihydroxypropyl)ether(BADGE.2H_(2)O),and bisphenol F diglycidyl ether(BFDGE)in 102 samples of several canned seafood,namely canned Antarctic krill,scallop,oysters,mussel,clam,and mantis shrimp stored for months at different temperatures through a high-performance liquid chromatographic-fluorescence detector com-bined with a microwave-assisted extraction method.Except for BFDGE,the other five bisphenols were observed in most of the analyzed sam-ples.The canned shrimp showed the highest migration of BPA(0.089 mg/kg),exceeding the specific migration limit(SML)of BPA(0.05 mg/kg)specified by the European Union,while the migration levels of BADGE and its derivatives were within their SMLs.The migration behavior of bisphenols in the canned seafood was majorly affected by the analytes,storage conditions,and food types.BPA,BADGE.H_(2)O,and BADGE 2H_(2)O were characterized by a rapid migration during the first half of the shelf life,which increased with the increase of temperature,followed by a stabilization or decline of their concentrations for prolonged durations.Besides,the migration of target bisphenols was significantly influenced by the storage temperature in some seafood species.Notably,higher migration level of BPA was found in samples with higher fat content.The average dietary exposure of Chinese adults to BPA,BPF,BADGE.2H_(2)O,BADGE.H_(2)O,and BADGE of canned seafood was estimated at 11.69,1.21,6.47,8.74,and 4.71 ng/(kg d),respectively.The target hazard quotient values of all the analyzed bisphenols were below 1 for the Chinese adults,suggesting an insignificant exposure to these bisphenols through canned seafood consumption.

SPECIAL ISSUE： MIGRANT WORKESR IN THE COURSE OF URBANIZATION Factors influencing the migration intentions of rural workers in the Pearl River Delta

The focus of this article is this question： under China＇s present household registration system, what factors influence migrant workers＇ decisions to obtain urban household registration in order to stay permanently in the city？ Our research finds that if willingness to give up their land is used as the indicator for behavioral permanent migration, the main factors that influence migrant workers＇ intention to migrate will be their individual motives for migration, i.e. choices based on economic rationality. If wishing to transfer their household registration to the cities where they work is used as the indicator for institutional permanent migration, the main factors that influence their intentions will be regional conditions and the pressure of institutional legitimacy, and their choices will be socially rational in that they are seeking institutional protection to improve their life in the city. Groups with different aspirations vary in their individual motivations for migration and the degree to which they feel the pressure of institutional legitimacy.