Chirality and asymmetric transformations of axially chiral 4,5-disubstituted phenanthreneamides

We have investigated the rotation barriers of 4-carbamoylphenanthrene and 4-thiocarbamoylphenanthrene and the asymmetric transformations of the novel 4-carboxy-5-carbamoylphenanthrenes. The similar ArC and CN barriers of 92 kJ/mol of 4-carbamoylphenanthrene indicate a strongly correlated process of both rotations. Only the corresponding thioamide could be separated on microcrystalline triacetylcellulose and a barrier of 115.6 kJ/mol was obtained from thermal racemization. Despite the large steric hindrance of the tightly interlocked substituents of the 4-carboxy-5-carbamoylphenanthrenes, the chirality became visible only at temperatures below −60°C by ¹H NMR spectroscopy. Only six of the eight possible stereoisomers, which may form four racemates, have been observed, namely two anti and one syn species. After the asymmetric transformation, one further syn arrangement is less populated or does not exist and the two anti isomers exist in an unequal ratio. Two orientations were found for the amide group: a major form A with the Me^E ‘outside’ and the carbonyl group ‘inside’ the bay-area and a minor form B with the reverse arrangement. The low barriers of 4-carboxy-5-carbamoylphenanthrenes indicate that steric hindrance and electrostatic repulsion in the transition state are compensated by correlated ArC and CN rotations and by twisting the phenanthrene plane. In the transition state, the carbonyl group passes the bay area and the pyramidal amide group passes H³ or H⁶ of the phenanthrene ring.     

考虑横法向热应变的C~0型Reddy板理论和三角形板单元

考虑横法向热变形,建议了C0型Reddy理论,并用于分析复合材料层合/夹层板热膨胀问题。虽然考虑了横法向热应变,但不增加额外的位移变量。此理论位移场不含有横向位移一阶导数,构造有限元时仅需C0插值函数。基于这一模型,运用虚位移原理推导了复合材料板平衡方程以及构造了6节点三角形板单元,并分析了简支复合材料层合/夹层板的热膨胀问题。数值结果表明,建立的模型能准确分析复合材料层合/夹层板热膨胀问题,而忽略横法向热应变的理论分析热膨胀问题误差较大。     

Two-dimensional probe absorption in coupled quantum dots

We investigate the two-dimensional (2D) probe absorption in coupled quantum dots. It is found that, due to the position-dependent quantum interference effect, the 2D optical absorption spectrum can be easily controlled via adjusting the system parameters. Thus, our scheme may provide some technological applications in solid-state quantum communication.     

Synthesis of reduced graphene oxide and enhancement of its electrical and optical properties by attaching Ag nanoparticles

Graphene has attracted the attention of the scientists and researchers because of its peculiar properties. Because of various unique properties, graphene can be used in sensing device applications, solar cells and liquid crystal display devices etc. In this research paper, we present a chemical route towards bulk production of r-GO (reduced graphene oxide). We have employed a modified method to achieve better results which is often termed as modified Hummer's and Offeman method. It is modified in terms of filtration technique. We have also attached silver nanoparticles (Ag-NP) to as synthesised r-GO. After successful growth, silver nanoparticles have been attached to r-GO by suitable treatment with AgNO₃ (aq.) N/50 solution. The as grown samples were characterised by FESEM, Raman Spectroscopy and EDS to make sure that r-GO and r-GO–Ag-NP have been successfully synthesised. The electrical and optical studies of the as grown samples were performed by dc conductivity measurements and UV visible spectroscopy. The conductivity was found to have increased with attachment of Ag-NP. The optical transmittance also improved to 90% as against 70% before Ag-NP attachment. The reduced graphene oxide attached with silver nanoparticles could find promising applications in synthesis of transparent electrode materials and optoelectronic devices.     

Pareto optimal design of layered bandgap materials with multiphase microstructures using evolutionary algorithms

An important characteristic of the periodic materials or structures is the existence of bandgap. This bandgap, which is dispersion-related, can be designed by controlling the materials layout within the periodic microstructures. In this paper, the topologies of periodic multiphase microstructures are optimized using a multiobjective genetic algorithm and two cases of studies are presented. The results show that 3-phase material can obtain quite better designs on the basis of fewer layers. This will be a reference for the design of phononic bandgap materials.     

Detecting low-dimensional chaos by the “noise titration” technique: Possible problems and remedies

Distinguishing low-dimensional chaos from noise is an important issue in time series analysis. Among the many methods proposed for this purpose is the noise titration technique, which quantifies the amount of noise that needs to be added to the signal to fully destroy its nonlinearity. Two groups of researchers recently have questioned the validity of the technique. In this paper, we report a broad range of situations where the noise titration technique fails, and offer solutions to fix the problems identified.     

High-quality ZnO nanorods grown on graphite substrates by chemical solution method

ZnO nanorods (NRs) were grown perpendicularly on graphite substrates using low-temperature wet chemical bath deposition (CBD) with sputtered ZnO film as seed layer. The individual ZnO NRs exhibit single-crystalline feature with well defined hexagonal prism shape and smooth side facets. The high optical qualities of ZnO NRs on graphite substrates were demonstrated by the dominant near-band edge emission and nearly undetectable deep level emissions in room-temperature photoluminescence spectra. The extremely low average reflectance of 0.45 % was obtained for the ZnO NRs/graphite structure in the spectra range from 200 to 1100 nm, indicating that the reported ZnO NRs/graphite structures have significant opportunity for potential application in high-performance photovoltaic devices. Considering the excellent material characteristics of ZnO NRs and the versatile and fascinating features of graphite substrates, the achievements make it possible for the development of high-performance ZnO-based nano-devices even in transferable, flexible, or stretchable forms.