Intensification of delignification of Tectona grandis saw dust as sustainable biomass using acoustic cavitational devices

Delignification of sawdust was studied using ultrasound assisted alkali peroxide approach using longitudinal horn for the first time and the efficacy compared with more commonly used configurations of ultrasonic reactors. Comparison with the conventional approach based on stirring has also been presented to establish the process intensification benefits. Effect of different operating parameters such as sodium carbonate concentration (0.1, 0.15, 0.2, 0.25 M), hydrogen peroxide concentration (0.2, 0.4, 0.6, 0.8, 1 M) and biomass loading (2, 4, 6, 8, 10 wt%), on the efficacy of lignin extraction has been investigated for different ultrasonic reactors. The optimum conditions for probe type ultrasonic horn were established as 150 W, 50% duty cycle and 80% amplitude with optimum process conditions as Na₂CO₃ concentration as 0.2 M, H₂O₂ concentration as 1 M, biomass loading of 10 wt% and operating time of 70 min. Longitudinal horn resulted in best efficacy (both in terms of yield and energy requirements) followed by ultrasonic horn and ultrasonic bath whereas the conventional approach was least effective. The obtained lignin was also analyzed using different characterization techniques. The presence of peaks at wavelength range of 875–817, 1123–1110, and at 1599 cm⁻¹ for the extracted sample confirmed the presence of lignin. Increase in the crystallinity index of the processed sample (maximum for longitudinal horn) also confirmed the lignin removal as lignin is amorphous in nature. Overall it has been concluded that ultrasound can be effectively used for delignification with longitudinal horn as best configuration.     

Molecular dynamic study of dielectric polarization and ferroelectricity in a model polar polymer

Molecular dynamics simulations are used to explore the polarization response of a lamellar crystal consisting of folded chains of a highly simplified model polar polymer. The system is based on a united atom model of polyethylene with constrained bond lengths and bond angles, and it is endowed with artificial partial charges placed on the united atoms to give it a simple polar character. Simulations performed with various temperatures, electric field directions, and electric field application histories reveal a complicated sequence of reorientation processes, including pronounced ferroelectric behavior. The sequence includes a weak, temperature‐independent prompt response, and a slow‐rising delay regime with stretched exponential behavior and thermally‐activated reorientation parameters consistent with trans‐gauche (TG) barrier crossings in the amorphous phase. When the delay regime has progressed sufficiently, a primary large‐amplitude response due to organized rotation of large subsegments in the crystalline phase occurs in a rapid manner that requires relatively few TG barrier crossings. A final, extremely slow rise in residual polarization completes the sequence. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 740–759     

Mechanical properties and thermal conductivity of the twisted graphene nanoribbons

Molecular dynamics method was used to simulate the twists of four GNRs (graphene nanoribbons), two AGNRs (armchair GNRs), and two ZGNRs (zigzag GNRs). Thermal conductivity of the length-fixing GNRs under torsion and at high temperature was calculated. It is found that the ZGNRs have better torsional rigidity than the AGNRs; under the torsional deformation of 34.2°/nm local buckling occurs in the length-fixing GNRs, and under the deformation of 22.8°/nm overall buckling occurs in the ones with free-length. In the range of investigated twist-angle and temperature, the thermal conductivity of the length-fixing GNRs decreases with the increase of torsional deformation and temperature. The wider GNRs have better anti-torsion capability and thermal conductivity.     

A note on the convexity of ruin probabilities

Conditions for the convexity of compound geometric tails and compound geometric convolution tails are established. The results are then applied to analyze the convexity of the ruin probability and the Laplace transform of the time to ruin in the classical compound Poisson risk model with and without diffusion. An application to an optimization problem is given.     

Thermally-Induced Isomerization of Prenucleation Clusters During the Prenucleation Stage of CdTe Quantum Dots

The evolution of prenucleation clusters in the prenucleation stage of colloidal semiconductor quantum dots (QDs) has remained unexplored. With CdTe as a model system, we show that substances form and isomerize prior to the nucleation and growth of QDs. Called precursor compounds (PCs), the prenucleation clusters are relatively optically transparent and can transform to absorbing magic-size clusters (MSCs). When a prenucleation-stage sample at 25, 45, or 80 °C is dispersed in a mixture of cyclohexane (CH) and octylamine (OTA) at room temperature, either MSC-371, MSC-417, or MSC-448 evolves with absorption peaking at 371, 417, or 448 nm, respectively. We propose that PC-371 forms at 25 °C, and isomerizes to PC-417 at 45 °C and to PC-448 at 80 °C. The PCs and MSCs are quasi isomers. Relatively large and small amounts of OTA favor PC-371 and PC-448 in dispersion, respectively. The present findings suggest the existence of PC-to-PC isomerization in the QD prenucleation stage.     

Sodium Carbazolide and Derivatives as Solid-State Electrolytes for Sodium-Ion Batteries

Replacing widely used organic liquid electrolytes with solid-state electrolytes (SSEs) could effectively solve the safety issues in sodium-ion batteries. Efforts on seeking novel solid-state electrolytes have been continued for decades. However, issues about SSEs still exist, such as low ionic conductivity at ambient temperature, difficulty in manufacturing, low electrochemical stability, poor compatibility with electrodes, etc. Here, sodium carbazolide (Na-CZ) and its THF-coordinated derivatives are rationally fabricated as Na⁺ conductors, and two of their crystal structures are successfully solved. Among these materials, THF-coordinated complexes exhibit fast Na⁺ conductivities, i.e., 1.20×10⁻⁴ S cm⁻¹ and 1.95×10⁻³ S cm⁻¹ at 90 °C for Na-CZ-1THF and Na-CZ-2THF, respectively, which are among the top Na⁺ conductors under the same condition. Furthermore, stable Na plating/stripping is observed even over 400 h cycling, showing outstanding interfacial stability and compatibility against Na electrode. More advantages such as ease of synthesis, low-cost, and cold pressing for molding can be obtained. In situ NMR results revealed that the evaporation of THF may play an essential role in the Na⁺ migration, where the movement of THF creates defects/vacancies and facilitates the migration of Na⁺.     

Selective Formal Carbene Insertion into Carbon-Boron Bonds of Diboronates by N-Trisylhydrazones

Bisborylalkanes play important roles in organic synthesis as versatile bifunctional reagents. The two boron moieties in these compounds can be selectively converted into other functional groups through cross-coupling, oxidation or radical reactions. Thus, the development of efficient methods for synthesizing bisborylalkanes is highly demanded. Herein we report a new strategy to access bisborylalkanes through the reaction of N-trisylhydrazones with diboronate, in which the bis(boryl) methane is transformed into 1,2-bis(boronates) via formal carbene insertion. Since the N-trisylhydrazones can be readily derived from the corresponding aldehydes, this strategy represents a practical synthesis of 1,2-diboronates with broad substrate scope. Mechanistic studies reveal an unusual neighboring group effect of 1,1-bis(boronates), which accounts for the observed regioselectivity when unsymmetric 1,1-diboronates are applied.     

单相旋转型驻波超声电机的数学模型及仿真

尽管单相驱动的旋转型驻波超声电机的原理样机早巳研制成功，但对这类电机的运动机理的研究却一直局限在定性分析上。本文将从能量角度，根据Hamilton变分原理，定、转子摩擦界面采用纯滑动模型建立了该种电机的数学模型；并根据此模型，用MATLAB语言作了计算机仿真，得到了该种电机的开、关过程动态响应。     

钢-混凝土组合梁受扭性能全过程分析

在合理假定的基础上，根据混凝土、钢梁和钢筋的本构关系，利用平衡及变形协调条件，推导出了适用于组合梁受扭全过程分析的一系列方程式，并提出了组合梁受扭分析的简化算法。然后，用VC 6．0编制了分析程序，制作了输入和输出的可视化界面。最后，对实验和理论分析结果进行了对比，结果表明方法合理，精度满足要求。