Tribological behaviors of three typical kinds of diamond-like carbon (DLC) films (a-C, a-C:Cr, and a-C:H) in sulfuric acid and sodium hydroxide solutions were investigated. The a-C film showed the lowest stable coefficients of friction (COF) in both sulfuric acid and sodium hydroxide solutions but the worst wear resistance in sulfuric acid solution. The a-C:H film showed the highest COF in sulfuric acid solution and the best wear resistance in both sulfuric acid and sodium hydroxide solutions. The a-C:Cr film exhibited superior comprehensive tribological performance in sulfuric acid solution, while in sodium hydroxide solution, high COF and very poor wear resistance was observed. What is more, friction and wear mechanism was revealed by investigating the friction-induced material evolutions on the sliding surface. 相似文献
Cellulose - A novel DOPO derived multi-claw reactive flame retardant (DMCFR) was designed to improve the flame retardancy of lyocell fabric. The chemical structure of DMCFR was identified by proton... 相似文献
In rolling production, the foil flatness quality is judged by detecting the lateral distribution of the front tension stress. Currently, because of the inaccuracy of the tension control model, there are still many flatness defects in foil rolling production. For the tension stress model of foil rolling, the primary problem is the inaccuracy of the metal lateral flow model. Therefore, based on Fleck’s foil rolling theory, a new model of the lateral displacement in the foil deformation region is established by using the principle of minimum potential energy. Next, a tension stress model is established, which takes the effect of the metal lateral flow into account. Last, using a laboratory 20-high rolling mill as the research object, the finite element model of foil rolling is established, and the accuracy of the new model is demonstrated by comparing the theoretical calculations with the simulation results.
Asymmetric 1,2-additions of cyanide yield enantioenriched cyanohydrins as versatile chiral building blocks. Next to HCN, volatile organic cyanide sources are usually used. Among them, cyanoformates are more attractive on technical scale than TMSCN for cost reasons, but catalytic productivity is usually lower. Here, the development of a new strategy for cyanations is described, in which this activity disadvantage is overcome. A Lewis acidic Al center cooperates with an aprotic onium moiety within a remarkably robust bifunctional Al–F–salen complex. This allowed for unprecedented turnover numbers of up to 104. DFT studies suggest an unexpected unique trimolecular pathway in which the ammonium bound cyanide attacks the aldehyde, which itself is activated by the carbonyl group of the cyanoformate binding to the Al center. In addition, a novel practical carboxycyanation method was developed that makes use of KCN as the sole cyanide source. The use of a pyrocarbonate as carboxylating reagent provided the best results. 相似文献
The side-on-end-on coordination of N2 can be very important to activate and functionalize this very stable molecule. However, such coordination has rarely been reported. This study reports a gas-phase species (a polynuclear vanadium nitride cluster anion [V5N5]−) that can capture N2 efficiently (12 %), and the quantum chemistry modelling suggests an unusual side-on-end-on coordination. The cluster anions were generated by laser ablation and the reaction with N2 has been characterized by mass spectrometry, photoelectron imaging spectroscopy, and density functional theory calculations. The back-donation interactions between the localized d–d bonding orbitals on the low-coordinated dual metal (V) sites and the antibonding π* orbitals of N2 are the driving forces to adsorb N2 with a high binding energy (about 2.0 eV). 相似文献
Suppose that X = {X_t, t≥0; P_μ} is a supercritical superprocess in a locally compact separable metric space E. Let φ0 be a positive eigenfunction corresponding to the first eigenvalue λ_0 of the generator of the mean semigroup of X. Then Mt := e~(-λ_0t)〈φ0,X_t〉 is a positive martingale. Let M_∞ be the limit of M_t. It is known(see Liu et al.(2009)) that M_∞ is non-degenerate if and only if the L log L condition is satisfied. In this paper we are mainly interested in the case when the L log L condition is not satisfied. We prove that, under some conditions, there exist a positive function γ_t on [0,∞) and a non-degenerate random variable W such that for any finite nonzero Borel measure μ on E,lim/t→∞γ_t〈φ0,X_t〉=W, a.s.-P_μ~.We also give the almost sure limit of γ_t〈f, X_t〉for a class of general test functions f. 相似文献
Cai and Zhang establish separate perturbation bounds for distances with spectral and Frobenius norms (Cai T, Zhang A. Rate‐optimal perturbation bounds for singular subspaces with applications to high‐dimensional statistics. The Annals of Statistics. 2018; Vol. 46, No. 1: 60?89). We extend their theorem to each unitarily invariant norm. It turns out that our estimation is optimal as well. 相似文献