Abstract-With the progress of society, traditional online learning platforms have demonstrated the uneven distribution of information resources, and teacher-student communication exhibits a certain delay. At present, cloud computing, which is a new product of information technology, has been favored in many areas because of its superior feedback mechanism and storage space. Therefore, to improve the integration of online learning information resources and facilitate interaction between teachers and students, we designed our own online learning system based on the Google cloud computing platform. We used Google's cloud computing platform and the Google App Engine to develop a unified and open online learning platform that is capable of storing large amounts of data, integrating considerable amounts of learning resources, and storing them on cloud. Through a test, we determined that the designed online learning platform for sharing information resources and integrating teacherstudent exchanges is highly beneficial. The platform helps the classroom learning atmosphere become active, and has a positive effect on teaching methods. The proposed platform can promote further development of online learning.

In this work, calcined chitosan-supported layered double hydroxides (CSLDO) were synthesized through a co-precipitation method that restrained the particles’ aggregation of LDHs and exhibited huge specific surface areas, which can enhance the fluoride adsorption capacity. CSLDOs were characterized by physical and chemical methods and used for fluoride adsorption in an aqueous solution. The results indicated that the nanoparticles were constructed first and then assembled to form a porous and layered structure, and chitosan-supported layered double hydroxides (CSLDHs) calcined at 400 °C (CSLDO400) showed the highest specific surface area of 116.98 m2·g−1 and the largest pore volume of 0.411 cm3·g−1. CSLDO400 exhibited excellent adsorption performance at a wide pH range from 5 to 9 for fluoride. The adsorption kinetics indicated that the adsorption reached equilibrium after 120 min, and followed a pseudo-first-order model. It agreed well with the Langmuir isotherm with maximum adsorption amounts of 27.56 mg·g−1. The adsorption of fluoride ions was spontaneous and endothermic. Furthermore, CSLDO400 showed a high stability for fluoride removal; it could still achieve 68% removal for fluoride after repeating five times of adsorption–desorption cycles. This study demonstrated that CSLDO400 is a promising functional material to remove fluoride from surface/ground water.

Structural, electronic,elastic and optical properties of ternary spinel oxides ZnFe2O4 have been studied by using first-principles calculation. The results show that all elastic constants are consistent with the mechanical stability criteria for cubic crystals, which indicated that ternary spinel oxides ZnFe2O4 are mechanically stable. The perfect spinel ZFO has the properties of direct bandgap semiconductor, which decreases with the increase of pressure.The DOS and Mulliken overall analysis shows that the Zn-O bonds and Fe-O bonds are covalent, and the Zn-O bond is stronger than the Fe-O bond. The results of the calculation show that the optical properties are in good agreement with the recent experimental results.