Conformational study of a guaiacyl beta-O-4 lignin model compound by NMR. Examination of intramolecular hydrogen bonding interactions and conformational flexibility in solution

Intramolecular H-bonding interactions were investigated in solution for the threo and erythro diastereomeric forms of a guaiacyl beta-O-4 lignin model compound by using the NMR data obtained from hydroxyl protons. Temperature coefficients of the chemical shifts (ddelta/dT) and coupling constants (3J(HCOH)) were measured in aprotic and protic solutions: DMSO-d6, acetone-d6 and acetone-d6-water. The NMR parameters do not support the existence of strong and persistent intramolecular H-bonds that could participate in the stabilization of the guaiacyl beta-O-4 structure in solution, but instead indicate that intermolecular H-bonds to solvent predominate. 1D NOE experiments nevertheless revealed the presence of a direct chemical exchange between the hydroxyl protons, suggesting the possible existence of weak and transient intramolecular H-bonding interactions. The conformational flexibility of the threo structure was also investigated in acetone solution from the measurement of long-range 1H, 1H and 1H, 13C coupling constants and from NOESY experiments. The NMR data are not consistent with any single conformation, indicating that different conformers co-exist in solution. The experimental results support the conformational flexibility predicted by molecular dynamics simulations performed in a previous study. Finally, both experimental and theoretical approaches indicate that weak intramolecular H-bonds can exist transiently in solution, breaking and reforming as the beta-O-4 molecule undergoes conformational interconversion, but cannot be invoked as possible means of conferring rigidity to the beta-O-4 structure.     

Flexible white top-emitting organic light-emitting diode with a MoO_x roughness improvement layer

In this paper, an MoOx film is deposited on a polyethylene terephthalate （PET） substrate as a buffer layer to improve the surface roughness of the flexible PET substrate. With an optimized MoOx thickness of 100 nm, the surface roughness of the PET substrate can be reduced to a very small value of 0.273 nm （much less than 0.585 nm of the pure PET）. Flexible white top-emitting organic light-emitting diodes （TEOLEDs） with red and blue dual phosphorescent emitting layers are constructed based on a low-reflectivity Sm/Ag semi-transparent cathode. The flexible white emission exhibits the best luminance and current injection characteristics with the 100-nm-thick MoOx buffer layer and this result indicates that a smooth substrate is beneficial to the enhancement of device electrical and electroluminescence performances. However, the white TEOLED with a 50-nm-thick MoOx buffer layer exhibits a maximum current efficiency of 4.64 cd/A and a power efficiency of 1.9 lm/W, slightly higher than those with a 100-nm MoOx buffer layer, which is mainly due to an obvious intensity enhancement but limited current increases in 50-nm MoOx-based white TEOLED. The change amplitudes of the Commission International de l’Eclairage （CIE） chromaticity coordinates are less than （0.016, 0.005） for all devices in a wide luminance range over 100 cd/m2, indicating an excellent color stability in our white flexible TEOLEDs. Additionally, the flexible white TEOLED with an MoOx buffer layer shows excellent flexibility to withstand more than 500 bending times under a curvature radius of approximately 9 mm. Research demonstrates that it is mainly attributed to the high surface energy of the MoOx buffer layer, which is conducible to the improvement of the surface adhesion to the PET substrate and the Ag anode.     

Development and Analysis of the Novel Hybridization of a Single-Flash Geothermal Power Plant with Biomass Driven sCO2-Steam Rankine Combined Cycle

This study investigates the hybridization scenario of a single-flash geothermal power plant with a biomass-driven sCO₂-steam Rankine combined cycle, where a solid local biomass source, olive residue, is used as a fuel. The hybrid power plant is modeled using the simulation software EBSILON^®Professional. A topping sCO₂ cycle is chosen due to its potential for flexible electricity generation. A synergy between the topping sCO₂ and bottoming steam Rankine cycles is achieved by a good temperature match between the coupling heat exchanger, where the waste heat from the topping cycle is utilized in the bottoming cycle. The high-temperature heat addition problem, common in sCO₂ cycles, is also eliminated by utilizing the heat in the flue gas in the bottoming cycle. Combined cycle thermal efficiency and a biomass-to-electricity conversion efficiency of 24.9% and 22.4% are achieved, respectively. The corresponding fuel consumption of the hybridized plant is found to be 2.2 kg/s.     

Amorphous hydrogenated carbon coatings on IC packaging mold by ECR-CVD system

The surface properties of IC packaging molds such as anti-sticking, wear, and corrosion resistances can be improved by hard surface coating. In this study, Ti/TiN/TiCN/a-C:H thin film coatings were deposited on IC cavity bar molds in a hybrid PVD-ECR-CVD coating system. The structure of the a-C:H films was delineated by a function of bias voltages by Raman spectroscopy. Excellent adhesion and lower friction coefficients of a-C:H films were also assessed. According to the normal adhesion force measurement, a-C:H coating was superior to that of typical electroplated hard chromium (Ep-Cr). Performance evaluation showed that the a-C:H coating could increase the number of molding injections in IC package production lines by 216%.     

A novel dynamic friction experiment using a modified kolsky bar apparatus

A novel dynamic friction experiment using the Kolsky bar concept was developed. The technique is complementary to the plate impact and other macroscopic friction experiments in the sense that sliding velocities and pressures not attainable otherwise can be investigated. The experimental results reported in this article show that the technique provides accurate and repeatable measurement of time-resolved friction. The apparatus is simpler and easier to operate than the plate impact facility. However, it cannot achieve the same level of contact pressure. Several material pairs have been investigated. In particular, the kinetic friction coefficient of Ti-6Al-4V sliding against WC/Co (cermet) and 4340 steel sliding against WC/Co were measured and compared with the values reported by Prakash and Clifton in 1993. Atomic force microscopy is used to characterize the surface topography before and after the friction tests.     

Lp ‐estimates for the Bergman projection on strictly pseudoconvex nonsmooth domains

We consider the Bergman projection on Henkin–Leiterer domains, bounded strictly pseudoconvex domains which have defining functions whose gradient is allowed to vanish. Our result describes the mapping properties of the Bergman projection between weighted L^p spaces, with the weights being powers of the gradient of the defining function. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

框架非线性分析的新梁柱单元

目前尚缺乏能在高轴力作用下简便地用于有限元分析的梁柱单元,本文所提出的单元运算简例,能以统一形式同时用于轴力P为拉（正）及压（负）的情况并在－3．8小于等于P／P,＜∞（P为杆的欧拉临界力）的范围内有极高的精度,实际上和作为精确解的稳定函数的精度相同,但能免除 稳定函数的精度相同,但能免除稳定函数需对轴力对拉,压及为零时采用三套不同公式的缺点,因此,该单元可用于所有实际框架结构的非线性分析,只需取一根杆件为一个单元,并且可简便地植入现有框架非线性分析程序中,文中还一些典型算例的分析结果,论证了单元的正确,高效和广泛适用性。     

Seven Conformations of the Macrocycle Cyclododecanone Unveiled by Microwave Spectroscopy

The physicochemical properties and reactivity of macrocycles are critically shaped by their conformations. In this work, we have identified seven conformations of the macrocyclic ketone cyclododecanone using chirped-pulse Fourier transform microwave spectroscopy in combination with ab initio and density functional theory calculations. Cyclododecanone is strongly biased towards adopting a square configuration of the heavy atom framework featuring three C–C bonds per side. The substitution and effective structures of this conformation have been determined through the observation of its ¹³C isotopologues. The minimisation of transannular interactions and, to a lesser extent, HCCH eclipsed configurations drive conformational preferences. Our results contribute to a better understanding of the intrinsic forces mediating structural choices in macrocycles.     

利用压杆技术确定与验证一些结构材料的塑性模型(英文)

提出了一种关于材料力学特性的综合研究方法,包括获取材料在宽大的应变率及温度范围下的必要的力学特性,确定或辨别材料的变形及破坏模型的必要参数,并通过特别的实验及数字模拟实验来检验或验证模型的适当性.通过对一些结构金属及合金材料的研究,展现了该方法的应用潜力.