Effect of carboxylic acid groups on the supercapacitive performance of functional carbon frameworks derived from bacterial cellulose

Three-dimensional(3D) carbonaceous materials derived from bacterial cellulose(BC) has been introduced as electrode for supercapacitors in recent. Here, we report a simple strategy for the synthesis of functional carbon frameworks through 2,2,6,6-tetramethylpilperidine 1-oxyl radical(TEMPO)-mediated oxidation of bacterial cellulose(BC) followed by carbonization. TEMPO-mediated oxidation can efficiently convert the hydroxyls on the surface of BC to carboxylate groups to improve electrochemical activity. Because of its high porosity, good hydrophilicity, rich oxygen groups, and continuous ion transport in-between sheet-like porous network, the TEMPO-oxidized BC delivers a much higher gravimetric capacitance(137.3 F/g) at low annealing temperature of 500℃ than that of pyrolysis BC(31 F/g) at the same annealing temperature. The pyrolysis modified BC obtained at 900℃ shows specific capacitance(160.2 F/g), large current stability and long-term stability(84.2% of its initial capacitance retention after 10,000 cycles).     

Assessment of the shear-improved Smagorinsky model in laminar-turbulent transitional channel flow

In this paper, the shear-improved Smagorinsky model (SISM) is assessed in a K-type transitional channel flow. Our numerical simulation results show that the original SISM model is still too dissipative to predict the transitional channel flow. Two former reported empirical correction approaches, including a low-Reynolds-number correction and a shape-factor-based intermittency correction, are applied to further promote the capability of the SISM model in simulating the transition process. Numerical tests show that the shape-factor-based intermittency correction approach can correctly improve the transition-prediction capability of the SISM model, while the low-Reynolds-number correction approach fails. Furthermore, the shape-factor-based intermittency-corrected SISM model can capture the vortical structures during the transitional process very well and possesses the grid-insensitive characteristics.     

Statistics and structures of pressure and density in compressible isotropic turbulence

We study statistics and structures of pressure and density in the presence of large-scale shock waves in a forced compressible isotropic turbulence using high-resolution numerical simulation. The spectra for pressure and density exhibit a ?2 scaling over an operational definition of the inertial range. Both the numerical simulation and a heuristic PDF model reveal that the PDFs of pressure increment exhibit a ?2 power law region for the separation in the operational definition of inertial range, quantitatively similar to the PDF of pressure gradient, which also displays a ?2 power law region. Moreover, the statistical relation between density increment and pressure increment has been investigated through a shock-relation model. There is a positive correlation between the vorticity magnitude and pressure, which is different from the case of incompressible turbulence. We argue that this difference is due to large-scale shock waves, another type of intermittent structures in addition to vortex structures in incompressible turbulence.     

A Modular Framework for Quantum-Proof Randomness Extractors

A quantum-proof extractor is a function that is used to extract randomness from any weakly random source X in the presence of prior quantum information about X. It is known that some constructions are quantum-proof, such as Trevisan’s construction. However, these extractors are generally restrictive for applications on the one-bit output construction and the weak design. Here, we give a modular framework to combine multi-bit output extractors (not only one-bit) with pseudorandom transform, and show that it is sound in the presence of quantum side information. Then combined with the theory of operator spaces, we improve previous theoretical proofs, and discuss the security of two-bit output extractor by giving a tighter bound for it.     

超低频振动能量收集器中夹片弹簧结构的建模与验证

针对一类基于夹片弹簧的压电振动能量收集器,利用材料力学莫尔积分理论建立了振荡俘能结构中夹片弹簧的等效刚度模型,通过万能拉伸试验机验证了模型精度.在此基础上,讨论了夹片弹簧刚度线性简化的两种途径:拉伸曲线线性拟合和固有频率修正.研究结果表明,从夹片弹簧拉伸曲线上看,将其等效成线性弹簧具有一定的合理性;而在实际振动能量收集器结构中,若振动加速度相对较小,通过固有频率修正法对夹片弹簧刚度进行线性简化,其幅频响应特性与非线性模型的特性相近.该研究成果为压电振动能量收集器的动力学和机电耦合模型简化提供了理论支撑.     

Self‐Assembly of Diblock Copolymers into Novel Snowflake‐Shaped Aggregates Driven by Quadruple Hydrogen Bonding

Two well‐defined diblock copolymers with quadruple hydrogen‐bonding groups on one block, denoted PSUEA‐1 and PSUEA‐2 , have been synthesized, and novel snowflake‐shaped nanometer‐scale aggregates, self‐assembled by such diblock copolymers in non‐polar solvents, have been observed. The micellar dimensions were investigated by DLLS and SLLS. Their morphologies were studied by TEM. Since the degrees of polymerization of the Upy‐containing blocks of PSUEA‐1 and PSUEA‐2 are quite similar and the polystyrene block of the PSUEA‐1 is longer than that of the PSUEA‐2 , a subtle but identifiable difference between the sizes and structures of the PSUEA‐1 and PSUEA‐2 aggregates was noticed and characterized.

     

无间隔层结构的高效率荧光/磷光混合型白光有机发光二极管

采用磷光红光/荧光蓝光/磷光绿光无间隔层三发光层结构,制备出了高效率荧光/磷光混合型白光有机发光二极管(OLEDs),其中选取具有高荧光量子产率(PLQY)的荧光染料4P-NPD(双[N-(1-萘基)-N-苯基-氨基]四联苯)作为蓝光发射分子,以及常用的高效磷光染料Ir(MDQ)₂(acac)和Ir(ppy)₃(acac)分别作为红光和绿光的客体,通过混合和掺杂的方法制备了相应的发光层,实现了发光层中激子的有效利用和白光发射。 制备的白光器件最大电流效率和功率效率分别达到了27.1 cd/A和30.3 lm/W,当电压为6 V时,CIE色坐标为(0.33,0.41),显色指数CRI为70,色温CCT为5432 K。 在此基础上,设计制备了高色温的荧光/磷光混合型白光OLEDs,其色温(CCT)达到了7106 K。     

网格生长动力学模型的建立和求解及其混合黏性网格生成中的应用1)

真实飞行器外形复杂,涉及的流动结构和现象对数值模拟中所需的网格提出了较高的要求。本文首先研究了各向异性黏性网格的生成方法,提出了网格生长动力学模型,并建立了松弛算法求解该模型,从而得到合理的层状网格;提出并建立了各向同性四面体网格的阵面推进Delaunay网格细化算法。最后通过数个算例对所建立的混合黏性网格生成方法的适用性和可靠性进行考察。结果表明,本文建立的混合黏性网格生成方法适用于复杂飞行器的网格生成,具有较高的可靠性。     

A ferrocene‐containing porous organic polymer linked by tetrahedral silicon‐centered units for gas sorption

A novel ferrocene‐containing porous organic polymer (FPOP) has been prepared by Sonogashira‐Hagihara coupling reaction of 1,1′‐dibromoferrocene and tetrakis(4‐ethynylphenyl)silane. Compared with other polymers, the resulting polymer possesses excellent thermal stability with the decomposition temperature of 415°C and high porosity with Brunauer–Emmett–Teller (BET) surface area of 542 m² g^?1 as measured by nitrogen adsorption‐desoprtion isotherm at 77 K. For applications, it shows moderate carbon dioxide uptakes of up to 1.42 mmol g^?1 (6.26 wt%) at 273 K/1.0 bar and 0.82 mmol g^?1 (3.62 wt%) at 298 K/1.0 bar, and hydrogen capacity of up to 0.45 mmol g^?1 (0.91 wt%) at 77 K/1.0 bar, indicating that FPOP might be utilized as a promising candidate for storing carbon dioxide and hydrogen. Although FPOP possesses lower porosity than many porous polymers, the gas capacities are higher or comparable to them, thereby revealing that the incorporation of ferrocene units into the network is an effective strategy to enhance the affinity between the framework and gas.     

Assembly and application advancement of organic‐functionalized graphene‐based materials: A review

Owing to the remarkable physicochemical properties such as hydrophobicity, conductivity, elasticity, and light weight, graphene‐based materials have emerged as one of the most appealing carbon allotropes in materials science and chemical engineering. Unfortunately, pristine graphene materials lack functional groups for further modification, severely hindering their practical applications. To render graphene materials with special characters for different applications, graphene oxide or reduced graphene oxide has been functionalized with different organic agents and assembled together, via covalent binding and various noncovalent forces such as π–π interaction, electrostatic interaction, and hydrogen bonding. In this review, we briefly discuss the state‐of‐the‐art synthetic strategies and properties of organic‐functionalized graphene‐based materials, and then, present the prospective applications of organic‐functionalized graphene‐based materials in sample preparation.