三维氧化铁/石墨烯的构建及其对CL-20的热分解性能的影响

High-performance solid propellants are very important for the development of modern weapons. Aside from their high energy and high burning rate, safety performance is regarded as the most important factor that should be considered whenever a new solid propellant recipe is formulated. Therefore, exploring a new type of combustion catalyst that can improve both catalytic activity and reduce the sensitivity of the energetic component is significant. Traditionally, transition metals or metal oxides are used as a combustion catalyst for accelerating the thermal decomposition of energetic components. However, the existing problem of these catalysts is the aggregation of particles accompanied by poor surface area. Coupling metal oxides with graphene is a promising approach to obtain a binary composite with stable structure and large specific surface area. In this work, rod-like and granular Fe₂O₃ nanoparticles were synthesized using a hydrothermal method. Then, the two as-prepared Fe₂O₃ nanoparticles were coupled with graphene sheets using an interfacial self-assembly method, which can effectively prevent the aggregation of Fe₂O₃ particles and simultaneously increase the active sites that participate in the reaction. X-ray diffraction and X-ray photoelectron spectroscopy were used to identify the phase states and chemical compositions of the prepared samples. The morphology and internal structures were further demonstrated through scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption tests. Both phase analysis and structure identification indicate that the prepared Fe₂O₃/G has high purity and high surface area. The catalytic performance of the prepared Fe₂O₃ and Fe₂O₃/G in the thermal decomposition of hexanitrohexaazaisowurtzitane (CL-20) was evaluated based on thermal gravimetric analysis-infrared spectroscopy (TGA-IR) and differential scanning calorimetry (DSC) tests. The non-isothermal decomposition kinetics of CL-20, Fe₂O₃/CL-20, and Fe₂O₃/G/CL-20 were further studied by DSC. The results reveal the excellent catalytic activity of Fe₂O₃/G in the thermal decomposition of CL-20, which is attributed to the presence of abundant pore structure and large surface area. The reaction mechanisms of the exothermic decomposition process of CL-20, Fe₂O₃/CL-20, and Fe₂O₃/G/CL-20 were obtained by the logical choice method, and the composites all followed same mechanism function model as CL-20. Through comparison, the rod-like Fe₂O₃ coupled with graphene was found to have the best catalytic activity in the thermal decomposition of CL-20. Thus, the rod-like Fe₂O₃ and its Fe₂O₃/G composite were used to investigate their influence on the impact sensitivity of CL-20 by fall hammer apparatus. The results show that rFe₂O₃/G can effectively decrease the impact sensitivity of CL-20 compared with pure CL-20 and rFe₂O₃/CL-20. Therefore, rFe₂O₃ coupled with graphene not only promotes the thermal decomposition but also improves the safety performance of CL-20.     

探究式与合作学习策略在药剂学教学实践中的应用探索

药剂学教学过程中需要应用多种教学手段与方法.为提高药剂学教学质量积累经验,紧密结合当前药剂学实验教学内容,开展探究式与小组合作学习策略在教学方法和成效上的研究,并根据教学实践,阐述了探究式与合作学习的新型教学方法的特点、运用条件及运用效果.     

Differential Properties of the Symmetric Matrix-Valued Fischer-Burmeister Function

This paper focuses on the study of differential properties of the symmetric matrix-valued Fischer–Burmeister (FB) function. As the main results, the formulas for the directional derivative, the B-subdifferential and the generalized Jacobian of the symmetric matrix-valued Fischer–Burmeister function are established, which can be utilized in designing implementable Newton-type algorithms for nonsmooth equations involving the symmetric matrix-valued FB function.     

Changing teaching practices toward effective mathematics instruction in the Korean context: characteristics and implications

Student-centered pedagogy has been consistently emphasized in many reform documents. This paper traces the process of changing traditional teacher-centered instruction toward a student-centered approach in the Korean context. By looking closely at the teacher’s successes and struggles, the paper attempts to understand better what constitutes the process of implementing new ideals into actual classroom contexts. The paper also analyzes what has changed and not changed in this teaching practice in order to reveal culturally specific values and expectations of mathematics instruction. Given that teaching practices of Korea have rarely been studied in international contexts, this paper is expected to foster an increase in the recent interest in effective mathematics instruction across different education systems.     

Physics perspectives of heavy-ion collisions at very high energy

The structure of stretchable electronics is based on the buckling of a thin film on a compliant substrate. Under anisotropic biaxial prestrains, this structure may buckle into several patterns, including cylindrical, checkerboard, and undulating patterns. The displacement and energy of each pattern are deduced analytically. By comparing their minimum potential energies, the critical buckling condition of each pattern is determined. After secondary bifurcation, the checkerboard pattern occurs just above the critical prestrains, but the undulating pattern dominates other regions. The buckling amplitude and wavenumber of the undulating pattern are shown under biaxial prestrains. Even if the structure is under equi-biaxial prestrains, it may buckle into an asymmetric undulating pattern.     

Simultaneous estimation of genetic linkage and preferential pairing factor for a triploid population with unphased markers

Triploids,recognized to occur more frequently in natural and experimental populations of many species than previously appreciated,display important economic and biological values.Despite this,however,linkage analysis for triploids has not been well explored.We develop a statistical model for estimating and testing the linkage between molecular markers in a triploid population derived from a tetraploid and diploid parent.The model incorporates one important meiotic feature of tetraploids by which more homologous chromosomes pair with a greater likelihood than less homologous chromosomes.By implementing the EM algorithm within the maximum likelihood framework,the model provides a procedure for simultaneous estimation of the linkage and preferential pairing factor.The model accommodates the segregating patterns of pseudotest markers and intercross markers with different amounts of informativeness.The utility of the model was validated through a real data analysis and simulation studies.The model provides a statistical tool for linkage analysis in a triploid population by taking into account meiotic behavior of tetraploids.Results from the model will help to shed light on the genetic diversity and origin of a polyploid population.     

Spin excitations in a K0.84Fe1.99Se2 superconductor as studied by MSssbauer spectroscopy

Mossbauer spectroscopy was used to probe the site-specific information of a K0.84Fe1.99Se2 superconductor. A spin excitation gap, △E≈5.5 meV, is observed by analyzing the temperature dependence of the hyperfine magnetic field （HMF） at the iron site within the spin wave theory. Using the simple model suggested in the literature, the temperature dependence of the HMF is well reproduced, suggesting that, below room temperature, the alkali metal intercalated iron selenide superconductors can be regarded as ferromagnetically coupled spin blocks that interact with each other antiferromagnetically to form the observed checkerboard-like magnetic structure.