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Compared with the application of Digital Twin (DT) in the industrial field, the application of DT in the field of education is still in its infancy. In this paper, a Digital Twin Campus (DTC) for teaching and learning is proposed. It is argued that DTC possesses two characteristics. First, DTC has a wide variety of employment orientations for students or teachers. Second, teaching-learning resources in DTC system is huge but divisible. These characteristics result in the optional difficulty for teaching-learning objects, i.e., curriculum resources, book information resources, and electronic-article resources. To solve this problem, this paper proposes a Double-layer Collaborative Filtering Algorithm Framework (DCFAF) to recommend teaching-learning objects for digital twin teachers or students in DTC. The recommended objects will be further optimized by simulation and prediction in the virtual space of DTC. DCFAF is designed based on the principle that similar teachers (or students) may prefer similar teaching-learning resources, and for the first time, it is given double-layer property by applying the divisible characteristics of teaching-learning resources. The double-layer property can effectively solve the problem of data sparsity in collaborative filtering algorithms. Finally, the superiority of DCFAF is verified on benchmark data sets including MovieLens100k and MovieLens1M which possess the above two characteristics of DTC. DTC constructed in this way can be expected to carry out simulation, prediction, optimization and feedback continuously with the help of DCFAF, so as to realize deep integration of the teaching-learning process between real campus and virtual campus to some extent.

Heuristic algorithms are gradually becoming a type of new promising methods for solving phase equilibrium calculation problems since they do not have to calculate an initial value in advance like traditional methods such as direct Newton's method and indirect thermodynamic method. A new heuristic optimizer, constrained linear prediction evolution algorithm (CLPE) for phase equilibrium calculation under given volume, temperature, and moles (NVT-flash) is proposed in this paper. CLPE employs the total Helmholtz free energy of the NVT-flash problem as its objective function and employs the volume and moles vector of a certain phase as decision variables. Numerical experiments are conducted on four NVT-flash problems. The consistency between the experimental results and those obtained by some traditional methods verifies that the proposed CLPE is effective. The comparative advantage in computational overhead over the similar algorithms indicates the significance of this study. The success of CLPE can drive more heuristic algorithms to solve NVT-flash problems more efficiently, so as to advance the field of phase equilibrium calculation. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) are believed to play a role in development of several diseases. L-ascorbic acid (AsA) is a kind of excellent antioxidant, but its instability in solution and hydrophilicity limits the wide use of it. Structural modifications of AsAby the introduction of lipophilic moieties can lead to derivatives with increased stability against thermal and oxidative degradation. In this study, a series of 6-O-acyl-L-ascorbic acid-2-O-phosphates (6-Acyl-AA-2Ps) were synthesized from a stable AsA derivative, L-ascorbic acid-2-phosphate ester magnesium (AA-2P) and long-chain fatty acids, act as radical scavengers for ROS and free radicals. ROS scavenging ability was investigated by CDCFH method in 95-D cells. The effect of 6-Acyl-AA-2P series on viability of 95-D cells was also studied by MTT method. All the synthesized compounds show stronger ROS scavenging ability and cytotoxicity than those of AsA. High-performance liquid chromatography assay demonstrates that 6-Acyl-AA-2Ps are stable in RPMI-1640 medium and can easily permeate cell membrane and be converted into AsA and L-ascorbic acid-2-phosphate ester. The results also show that the activity of 6-Acyl-AA-2Ps increases with a decrease in the length of the alkyl chain but cytotoxicity decreases. The optimum length of alkyl side chain is 12 carbons. In summary, 6-Laur-AA-2P should be one of the best candidates for the development of an efficient new AsA derivative and should be further investigated in detail.

A novel procedure for the direct separation and purification of prodigiosin based on adsorption chromatography is provided. A surfactant (Tween 80; 0.1%, w/v) was used to improve prodigiosin release from the cell envelope. An adsorbent (X-5 resin) with high loading capacity (7.3 mg/g) was selected for the direct recovery of prodigiosin from culture broth by static adsorption or in situ separation. This technology not only simplified the separation process, but also made the recovery yield (83%) much higher when compared with the conventional method (50%). As a result, it will be particularly suited for large-scale separation and purification of prodigiosin.