35Cl NMR研究溶液中离子对和离子缔合

测量了Sr和Ba高氯酸盐在乙腈和乙醇中0.5 mol·L~(-1)溶液的~(35)Cl NMR峰宽Δv和粘度η。按核四极矩弛豫机理, 结合文献中Mg~[1]和Ca~[2]盐的数据, 一种溶剂中各盐的Δv/η之比当反映~(35)Cl核处的电场梯度平方之比。按接触型离子对假设, ~(35)Cl处电场梯度平方之比应等于(r_++r_-)~(-6)。测得各盐的Δv/η之比与计算的(r_++r_-)~(-6)吻合, 论证了在乙腈与乙醇中为接触型离子对。同时文中报告了Δv/η和盐的摩尔电导随水或DMF加入的变化。     

Na(110)和Na2O(111)表面弛豫的研究

We have studied the relaxation of Na(110) and Na_2O(111) surfaces with LEED, and found that the best agreement between theory and experiment in such a structure, the surface layer distance d=0.291±0.01 nm (contracted 0.34%±0.01 nm) [for Na(110)]; and the three atomic surface layer distances d_1=0.117±0.01 nm (expanded 4.63%±0.01 nm), d_2=0.161±0.01 nm(expanded 0.063%±0.01 nm) and d_3=0.086±0.01 nm (expanded 0.75%±0.01 nm) [for Na_2O(111)].     

Synthesis and characterization of polydimethylsiloxane-cured organically modified silicate hybrid coatings

Hybrid coatings based on polydimethylsiloxane-cured organically modified silicate were synthesized through a sol-gel technique. Amino-terminated siloxane, 3-glycidoxypropyltrimethoxysilane and tetraethoxysilane were used as precursors for the hybrid coatings. These hybrid films were deposited via spin coating onto an aluminum alloy to improve the corrosion protection. The effects induced by the different chain lengths of siloxane on the chain dynamics, thermal stability and corrosion performance of the coated samples were investigated. The rotating-frame spin-lattice relaxation times and scale of the spin-diffusion path length indicated that the configuration of the hybrid films was highly crosslinked, dense and adhered to the aluminum alloy substrates. The thermal stability and the apparent activation energy, evaluated by van Krevelen's method, of the hybrid coatings depended on the siloxane chain length. Potentiodynamic analysis revealed that the hybrid films provided exceptional barrier and corrosion protection in comparison with untreated aluminum alloy substrates.     

溶液中尼龙11的NMR弛豫研究

用 2DNMR(HMQC)技术归属了溶液中尼龙 11分子的主要1H和13 C NMR共振信号 ,并通过变温和变浓度 1H NMR弛豫时间的测定 ,得到了尼龙 11溶液中氢键结构变化的动力学信息 .结果表明 ,溶液中尼龙 11分子的弛豫行为与一般高聚物不同 ,随着温度升高 ,尼龙链间相互作用逐渐减弱 ,尼龙分子与溶剂小分子间相互作用逐渐增强 ,尼龙链间氢键逐渐离解 ,而离解出来的自由NH和CO基团又与溶剂小分子间生成氢键 .尼龙 11链卷曲堆积成无规线团状 ,一部分溶剂被包裹在内部并和α CO质子成为一个整体而一起运动 .变浓度实验弛豫过程呈现双指数特性 ,快弛豫部分随体系浓度增加而增多 ,表明聚合物溶液中凝聚缠结含量的增大 ,这种凝聚缠结是由溶液中氢键引起分子链物理交联成网而形成的 .随着浓度增加 ,溶液逐渐变成局部粘度较大的类似软固体     

On temperature- and space-dimension dependent matter agglomerations in a mature growing stage

Model matter agglomerations, with temperature as leading control parameter, have been considered, and some of their characteristics have been studied. The primary interest has been focused on the grain volume fluctuations, the magnitude of which readily differentiates between two commonly encountered types of matter agglomeration/aggregation processes, observed roughly for high- and low-density matter organizations. The two distinguished types of matter arrangements have been described through the (entropic) potential driving the system. The impact of the potential type on the character of matter agglomeration has been studied, preferentially for (low-density) matter aggregation for which a logarithmic measure of its speed has been proposed. A common matter diffusion as well as mechanical relaxation picture, emerging during the mature growing stage, has been drawn using a phenomenological line of argumentation. Applications, mostly towards obtaining soft agglomerates or so-called jammed materials, have been mentioned.     

Relaxational and Associative Aspects of X…HO Bond Complexes

Relaxational and associative aspects of X…HO bond complexes in ternary liquid mixtures of aromatic halogen compounds, namely, chlorobenzene and bromobenzene with ethanol in benzene have been studied at 10 GHz frequency and a temperature range of 30-60°C using dielectric relaxation data. Due to the observed high values of distribution parameter, the relaxation mechanism has been further resolved in terms of two separate relaxation times. The dipole moment, association equilibrium constant and thermodynamic parameters associated with the complexes have also been determined. All the results indicate the occurrence of weak molecular interaction in both the systems. This is in agreement with the ultrasonic results on these systems, reported earlier by Kannappan and Palani.     

On relaxed greedy randomized Kaczmarz methods for solving large sparse linear systems

For solving large sparse systems of linear equations by iteration methods, we further generalize the greedy randomized Kaczmarz method by introducing a relaxation parameter in the involved probability criterion, obtaining a class of relaxed greedy randomized Kaczmarz methods. We prove the convergence of these methods when the linear system is consistent, and show that these methods can be more efficient than the greedy randomized Kaczmarz method if the relaxation parameter is chosen appropriately.     

Liquid State Relaxation Processes of Electronically Excited Luminophors Detected by Time-Resolved Spectroscopy and Travelling Wave Dye Lasers

Experimental findings concerning liquid state relaxation processes of electronically excited molecules, coming from time-resolved spectroscopy and travelling wave dye lasers, offer a formidable basis for restructuring some of the theories dealing with relaxation processes. Comparison of the prime research literature with standard texts shows a severe time lag in the dissemination of essential concepts, while comparison of ‘traditional’ fluorescence with intra-cavity photon emission reveals basic differences involving relativistic effects and vector space construction, mitigating against the practice of directly incorporating laser based data into ordinary chemical dynamics.     

Correlative analysis between morphology and mechanical properties of poly-3-hydroxybutyrate (PHB) blended with polycarprolactone (PCL) using solid-state NMR

Blends of poly(3-hydroxybutyrate) (PHB) and poly(caprolactone) (PCL) were evaluated using multiscale instrumental analyses to reveal the effects of blend ratio and crosslinking reagent. In the multiscale instrumental analyses, molecular mobility from molecular to nano scales was examined by solid-state NMR, while the morphology at the micron scale was revealed by scanning electron microscopy (SEM). PHB-rich blends adopted a sea-island morphology and showed a larger maximum stress due to dispersed PHB filler. A PCL-rich blend also adopted a sea-island morphology but the sea domain consisted of PCL and showed a larger strain at break. An equal ratio PHB/PCL blend had a bicontinuous morphology which showed lower maximum stress and lower strain at break because of large hemispherical defects. The crosslinking reagent changes these heterogeneous morphologies of PHB/PCL blends to homogeneous at the micron scale, which improved tensile properties. Even though the molecular mobility changed with the polymer content and the crosslinking reagent, the bicontinuous and homogeneous morphologies more significantly affected the tensile properties of the PHB/PCL blends.     

Surrogate based sensitivity analysis of process equipment

The computational cost associated with the use of high-fidelity computational fluid dynamics (CFD) models poses a serious impediment to the successful application of formal sensitivity analysis in engineering design. Even though advances in computing hardware and parallel processing have reduced costs by orders of magnitude over the last few decades, the fidelity with which engineers desire to model engineering systems has also increased considerably. Evaluation of such high-fidelity models may take significant computational time for complex geometries.