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In e-learning, the increasing number of learning resources makes it difficult for learners to find suitable learning resources. In addition, learners may have different preferences and cognitive abilities for learning resources, where differences in learners' cognitive abilities will lead to different importance of learning resources. Therefore, recommending personalized learning paths for learners has become a research hotspot. Considering learners' preferences and the importance of learning resources, this paper proposes a learning path recommendation algorithm based on knowledge graph. We construct a multi-dimensional courses knowledge graph in computer field (MCCKG), and then propose a method based on graph convolutional network for modeling high-order correlations on the knowledge graph to more accurately capture learners' preferences. Furthermore, the importance of learning resources is calculated by using the characteristics of learning resources in the MCCKG and learners' characteristics. Finally, by weighting the two factors of learners' preferences and the importance of learning resources, we recommend the optimal learning path for learners. Our method is evaluated from the aspects of learner's satisfaction, algorithm effectiveness, etc. The experimental results show that the method proposed in this paper can recommend a personalized learning path to satisfy the needs of learners, thus reducing the workload of manually planning learning paths. [ABSTRACT FROM AUTHOR]

Covalent organic nanosheets (CONs) are receiving tremendous interest for their potential in versatile applications. However, the synthesis of CONs usually suffers from the use of toxic solvents, low yields and uncontrollable thickness. Here, we report a green, high yield, and scalable strategy to strip two-dimensional imine-linked covalent organic framework (COF) powders in water using bi-functional ionic liquids as both the intercalator and stabilizer under ambient conditions. It is shown that the exfoliation yield reaches up to 66.6%, which is a record value for the delamination of CONs from bulk COF powder. The thickness of CONs is mainly in the range from 0.4 to 2.0 nm and the lateral size is large up to a few hundred nanometers. Importantly, the aqueous IL solutions can be reused and recycled for the exfoliation of CONs. The acid–base and hydrogen bond interactions between CONs and cations of the ILs are found to play critical roles in the delamination and stability of CONs. Furthermore, the CONs without any additives such as metals, photosensitizers, and sacrificial agents have been used as catalysts for photocatalytic CO2 reduction with gaseous water to yield CO in the gas phase under visible-light irradiation. The production rate of CO is 132.2 μmol g−1 h−1, which is twice that by the bulk COF powder, and outperforms most visible-light driven metal-free COFs reported so far. Therefore, the liquid phase stripping approach reported here possesses tremendous potentiality in mass production of CONs for high efficiency photocatalysis of CO2 reduction in the gas phase. [ABSTRACT FROM AUTHOR]

Gold nanoclusters (AuNCs) have received extensive attention due to their outstanding biocompatibility and excellent optical and electrochemical properties. However, the disadvantages of lower quantum yield (QY, usually <10%) and time-consuming synthetic processes severely limit their wide applications. Herein, a rapid and convenient synthetic strategy for AuNCs with higher QY is developed. AuNCs with excellent photo-/thermal stability can be one-pot-synthesized in several minutes only using vitamin B1 (VB1) as both the stabilizer and reducing agent at room temperature, which can be used for the large-scale synthesis of AuNCs. More interesting is that the QY of AuNCs@VB1 can be easily modulated by pyridine (Py) and greatly enhanced to 66.27% (AuNCs@VB1/Py). To our knowledge, this is the first report on the synthesis of AuNCs with higher QY in several minutes using VB1 as a protective agent. The QY enhancement mechanism of AuNCs@VB1/Py is also investigated in detail, and it is proven that the electron injection from Py to AuNCs accelerates the irradiative transition and thus increases its fluorescent emission. Furthermore, fluorescence sensing for glutathione (GSH) and hypochlorite detection has been successfully constructed based on the suppressed fluorescence of AuNCs@VB1/Py by GSH and then restored by hypochlorite. In brief, this work offers a convenient strategy for rapid and large-scale synthesis of AuNCs with higher QY, which will have a wide range of applications in the fields of biolabeling, sensing, bioimaging, and so on. [ABSTRACT FROM AUTHOR]

Phase transfer of metal–organic frameworks is highly desired in many areas, which remains a challenge. Herein, we present for the first time a CO2-driven reversible transfer of amine-functionalized ZIF-90 between organics and water. A mechanistic study showed that the switching is ascribed to the reversible generation of hydrophilic ammonium salts from the reaction of CO2 with the amines on ZIF-90. This unique system has been used for the coupling of trans-esterification reactions, product separation and component recycling for green sustainable processes. This work opens up a new avenue for performing reactions effectively with an easy separation process. [ABSTRACT FROM AUTHOR]

Application of chemical cues to manipulate adult sea lamprey (Petromyzon marinus) behavior is among the options considered for new sea lamprey control techniques in the Laurentian Great Lakes. A male mating pheromone component, 7α,12α,24-trihydroxy-3-one-5α-cholan-24-sulfate (3kPZS), lures ovulated female sea lamprey upstream into baited traps in experimental contexts with no odorant competition. A critical knowledge gap is whether this single pheromone component influences adult sea lamprey behavior in management contexts containing free-ranging sea lampreys. A solution of 3kPZS to reach a final in-stream concentration of [10.sup.-12] mol x [L.sup.-1] was applied to eight Michigan streams at existing sea lamprey traps over 3 years, and catch rates were compared between paired 3kPZS-baited and unbaited traps. 3kPZS-baited traps captured significantly more sexually immature and mature sea lampreys, and overall yearly trapping efficiency within a stream averaged 10% higher during years when 3kPZS was applied. Video analysis of a trap funnel showed that the likelihood of sea lamprey trap entry after trap encounter was higher when the trap was 3kPZS baited. Our approach serves as a model for the development of similar control tools for sea lamprey and other aquatic invaders. L'utilisation de signaux chimiques pour manipuler le comportement de lamproies marines (Petromyzon marinus) adultes est une des options examinees parmi les nouvelles techniques de controle des lamproies dans les Grands Lacs laurentiens. Un compose pheromonal d'accouplement male, le 7[alfa],12[alfa],24-trihydroxy-3-one-5[alfa]-cholan-24-sulfate (3kPZS), attire les lamproies femelles ovulees vers l'amont dans des cages appatees en contexte experimental sans concurrence olfactive. Une lacune critique sur le plan des connaissances consiste a savoir si ce seul compose pheromonal influence le comportement des lamproies marines adultes dans des contextes de gestion contenant des lamproies marines en liberte. Une solution de [10.sup.-12] mol x [L.sup.-13]kPZS a ete appliquee a huit cours d'eau du Michigan en des endroits ou sont disposees de cages a lamproies sur une periode de trois ans, et une comparaison des taux de prises de cages appatees au 3kPZS et non appatees jumelees a ete effectuee. Des nombres significativement plus grands de lamproies sexuellement immatures et matures ont ete capturees dans les cages appatees, et l'efficacite annuelle globale des cages dans un cours d'eau donne etait en moyenne 10 % plus elevee durant les annees ou du 3kPZS avait ete applique. L'analyse video de la goulotte d'une cage a demontre que la probabilite qu'une lamproie entre dans une cage apres avoir decele sa presence etait plus elevee quand la cage etait appatee avec du 3kPZS. Notre approche constitue un modele pour la mise au point d'outils de controle semblables des lamproies marines et autres especes aquatiques envahissantes. [Traduit par la Redaction], Introduction The invasion of sea lamprey (Petromyzon marinus), a native of the Atlantic Ocean, into the upper Laurentian Great Lakes has precipitated a series of undesirable biological changes in this [...]

A novel alternative is presented for the extraction and preconcentration of polycyclic aromatic hydrocarbons (PAH) from water samples. The new approach--which we have named solid-phase nanoextraction (SPNE)--takes advantage of the strong affinity that exists between PAH and gold nanoparticles. Carefully optimization of experimental parameters has led to a high-performance liquid chromatography method with excellent analytical figures of merit. Its most striking feature correlates to the small volume of water sample (500 [micro]L) for complete PAH analyses. The limits of detection ranged from 0.9 (anthracene) to 58 ng x [L.sup.-1] (fluorene). The relative standard deviations at medium calibration concentrations vary from 3.2 (acenaphthene) to 9.1% (naphthalene). The analytical recoveries from tap water samples of the six regulated PAH varied from 83.3 [+ or -] 2.4 (benzo[k]fluoranthene) to 95.7 [+ or -] 4.1% (benzo[g,h,i]perylene). The entire extraction procedure consumes less than 100 [micro]L of organic solvents per sample, which makes it environmentally friendly. The small volume of extracting solution makes SPNE a relatively inexpensive extraction approach.

Recording absorption spectra via transmittance through frozen matrixes is a challenging task. The main reason is the difficulty in overcoming the strong scattering light reaching the detector. This is particularly true when thick samples are necessary for recording absorption spectra of weak oscillators. In the case of strongly fluorescent compounds, additional errors in absorbance measurements arise from the emission reaching the detector, which might have an intensity comparable to that of the transmitted light. This article presents a fundamentally different approach to low-temperature absorption measurements as the sought for information is the intensity of laser excitation returning from the frozen sample to the ICCD. Laser excitation is collected with the aid of a cryogenic fiber optic probe. The feasibility of our approach is demonstrated with single-site and multiple-site Shpol'skii systems. The 4.2 K absorption spectra show excellent agreement with their literature counterparts recorded via transmittance with closed-cycle cryogenators. Fluorescence quantum yields measured at room temperature compare well to experimental data acquired in our laboratory via classical methodology. Similar agreement is observed between 77 K fluorescence quantum yields and previously reported data acquired with classical methodology. We then extend our approach to generate original data on fluorescence quantum yields at 4.2 K.

Nowadays, the spread of Internet rumors and viruses has caused great hidden dangers to the safety of human life. It is particularly important to identify the source of network threat, especially when there are multiple sources in the network. At present, the research on multi-source propagation is mostly based on SI model, but there is little work on multi-source propagation under SIR model. Based on SIR propagation model, this paper proposes a novel PRIA algorithm to locate multiple propagation sources. Firstly, we propose a new partitioning method based on effective distance, which transforms the source problem into a single source problem in multiple partitions. Secondly, we propose a single source algorithm based on SIR propagation model, which uses reverse infection algorithm to locate suspicious sources. Finally, we evaluate our approach in real network topology. The simulation results show that our method can effectively identify the real source and estimate the propagation time. And it has great accuracy in the number of identification sources. [ABSTRACT FROM AUTHOR]