High precision polishing of aluminum alloy mirrors through a combination of magnetorheological finishing and chemical mechanical polishing.

After the aluminum alloy mirror machined by single point diamond turning (SPDT), the residual tool marks and surface accuracy of the aluminum alloy mirror cannot meet the requirements of visible or ultraviolet light system. In this study, a processing method combining magnetorheological finishing (MRF) and chemical mechanical polishing (CMP) is proposed to realize the polishing of aluminum alloy mirrors with high efficiency, high precision and high-quality. Firstly, the properties and composition of passivation layer after MRF were analyzed and the polishing performance of acidic, neutral and alkaline alumina polishing fluid on passivation layer were investigated based on the computer numerical control (CNC) polishing equipment. Based on the experimental results, a new acidic nano-silica polishing fluid which is suitable for the efficient and high-quality removal of passivation layers on aluminum alloy surfaces was developed. Finally, a combined approach of MRF-CMP was used to the directly polishing of a rapidly solidified aluminum mirror (RSA-6061) with a diameter of 100 mm after SPDT. With two iterative of MRF-CMP polishing in 220 minutes, the surface accuracy of the aluminum alloy mirror was improved from 0.1λ (λ=632.8 nm) to 0.024λ, and the surface roughness (Ra) decreased from 3.6 nm to 1.38 nm. The experiment results manifest that high precision, and high-quality aluminum alloy mirror can be achieved by MRF-CMP method with the new developed acid nano-silica polishing fluid and suitable MR polishing fluid. The research results will provide a new strategy for ultra-precision direct polishing of aluminum alloy mirrors and will also give the important technical support for the extensive use of aluminum alloy mirror in visible light and ultraviolet optical systems.

Elastoplastic contact model of pitch-based rough surface and its polishing characteristics.

Fused silica glass is widely used in optical systems, including astronomical telescopes, laser systems, optical communications, and the semiconductor industry. At the same time, the surface quality of the fused silica directly determines the performance and precision of the system. In order to analyze the microscopic surface interaction based on the basis of tribology, a roughness contact model of pitch and fused silica glass surfaces was established. Analyze the performance parameters of contact materials, surface roughness, and the relationship between load and contact area. Pitch materials with a higher plasticity index have a larger elastoplastic contact area with the fused silica surface during the polishing process. The experimental results demonstrate that the surface quality of the polished fused silica improves as the plasticity index of the pitch material increases. At the same time, judging from the PSD curve results, the polished surface of the No. 55 pitch on the spatial-frequency band curve (100-101/mm) is significantly lower than the other two brands of pitch. Additionally, the Ra value of the workpiece surface roughness reaches 0.091 nm. The results of this study provide important theoretical guidance for achieving full-diameter, full-frequency ultra-smooth polishing of large-diameter complex curved surfaces.

Microwave-Assisted One Pot Cascade Conversion of Furfural to γ-Valerolactone over Sc(OTf)3.

γ-Valerolactone (GVL) is considered as a star biochemical which can be used as a green solvent, fuel additive and versatile organic intermediate. In this study, metal triflate (M(OTf)n ) was utilized as the catalyst for one-pot transformation of furfural (FF) to GVL in alcohol media under microwave irradiation. Alcohol plays multiple functions including solvent, hydrogen donor and alcoholysis reagent in this cascade reaction process. And process efficiency of GVL production from FF upgrading is strongly related to the effective charge density of selected catalyst and the reduction potential of selected alcohol. Complex (OTf)n -M-O(H)R, presenting both Brønsted acid and Lewis acid, is the real catalytic active species in this cascade reaction process. Among various catalysts, Sc(OTf)3 exhibited the best catalytic activity for GVL production. Various reaction parameters including the Sc(OTf)3 amount, reaction temperature and time were optimized by the response surface methodology with the central composite design (RSM-CCD). Up to 81.2 % GVL yield and 100 % FF conversion were achieved at 143.9 °C after 8.1 h in the presence of 0.16 mmol catalyst. This catalyst exhibits high reusability and can be regenerated by oxidative degradation of humins. In addition, a plausible cascade reaction network was proposed based on the distribution of product.

Recent advances in catalytic synthesis of 2,5-furandimethanol from 5-hydroxymethylfurfural and carbohydrates.

5-Hydroxymethylfurfural (HMF) is a versatile platform chemical derived from the dehydration of renewable carbohydrates (typically glucose/fructose-based monosaccharides, oligosaccharides, and polysaccharides). Some useful compounds, such as 2,5-furandimethanol (FDM), 2,5-dimethylfuran (DMF) and 2,5-dimethyltetrahydrofuran (DMTHF), have been synthesized by reduction of HMF. Among these, FDM is a promising diol and can be further converted towards fine chemicals, liquid fuels and polymer materials. In this review, some typical catalytic systems for the synthesis of FDM from both HMF and carbohydrates were summarized. The discussion focused on controlling the reaction networks for the reduction of HMF. The reaction mechanisms and the stability of the catalysts were introduced briefly. Last but not least, the prospects of effective production of FDM were discussed as well.

Neural network assisted Kalman filter for INS/UWB integrated seamless quadrotor localization.

Due to some harsh indoor environments, the signal of the ultra wide band (UWB) may be lost, which makes the data fusion filter can not work. For overcoming this problem, the neural network (NN) assisted Kalman filter (KF) for fusing the UWB and the inertial navigation system (INS) data seamlessly is present in this work. In this approach, when the UWB data is available, both the UWB and the INS are able to provide the position information of the quadrotor, and thus, the KF is used to provide the localization information by the fusion of position difference between the INS and the UWB, meanwhile, the KF can provide the estimation of the INS position error, which is able to assist the NN to build the mapping between the state vector and the measurement vector off-line. The NN can estimate the KF's measurement when the UWB data is unavailable. For confirming the effectiveness of the proposed method, one real test has been done. The test's results demonstrate that the proposed NN assisted KF is effective to the fusion of INS and UWB data seamlessly, which shows obvious improvement of localization accuracy. Compared with the LS-SVM assisted KF, the proposed NN assisted KF is able to reduce the localization error by about 54.34%.

One-pot conversion of dihydroxyacetone into ethyl lactate by Zr-based catalysts.

Efficient strategies for producing bio-based reagents from sustainable biomass are highly attractive for cost-effective sustainable manufacturing. In this study, a series of eco-friendly Zr-based catalysts (basic zirconium carbonate, zirconium dioxide and zirconium hydroxide) were investigated for the efficient conversion of dihydroxyacetone to ethyl lactate in a one-pot system, in which basic zirconium carbonate exhibited the best performance with 100% dihydroxyacetone conversion and 85.3% EL (ethyl lactate) yield at 140 °C, 4.0 h and 1.0 MPa N2. The improved activity of basic zirconium carbonate could be attributed to the synergistic effect among acid and base active sites. Furthermore, this low-cost catalyst shows improved thermochemical stability and recyclability under optimal conditions, where no significant decrease in activity was observed after three runs. This catalytic process could be identified as a promising alternative to produce ethyl lactate from renewable biomass and its derivatives.

Structural Studies of Giant Empty and Endohedral Fullerenes.

Structure elucidations of giant fullerenes composed of 100 or more carbon atoms are severely hampered by their extremely low yield, poor solubility and huge numbers of possible cage isomers. High-temperature exohedral chlorination followed by X-ray single crystal diffraction studies of the chloro derivatives offers a practical solution for structure elucidations of giant fullerenes. Various isomers of giant fullerenes have been determined by this method, specially, non-classical giant fullerenes containing heptagons generated by the skeletal transformations of carbon cages. Alternatively, giant fullerenes can be also stabilized by encapsulating metal atoms or clusters through intramolecular electron transfer from the encapsulated species to the outer fullerene cage. In this review, we present a comprehensive overview on synthesis, separation and structural elucidation of giant fullerenes. The isomer structures, chlorination patterns of a series of giant fullerenes C2n (2n = 100-108) and heptagon-containing non-classical fullerenes derived from giant fullerenes are summarized. On the other hand, giant endohedral fullerenes bearing different endohedral species are also discussed. At the end, we propose an outlook on the future development of giant fullerenes.

Towards Shell Biorefinery: Advances in Chemical-Catalytic Conversion of Chitin Biomass to Organonitrogen Chemicals.

Chitin is the most abundant biopolymer after cellulose but it has not been fully utilized yet. Because of biologically fixed nitrogen, effective conversion of chitin or its derivatives to value-added organonitrogen compounds is a promising strategy to valorize chitin biomass, which has attracted increasing attention. Recently, a novel concept of shell biorefinery has been proposed on account of the huge potentials of chitin valorization. Until now, a number of valuable organonitrogen chemicals, including amino sugars, amino alcohols, amino acids, and heterocyclic compounds, have been produced from chitin biomass. In this Minireview, the focus is on the recent advances in the synthesis of organonitrogen chemicals employing chitin biomass as starting material via different catalytic processes. An outlook on the challenges and opportunities for more effective valorization of chitin will be given.

Dialysis membrane enclosed laccase catalysis combines a controlled conversion rate and recyclability without enzyme immobilization.

Laccase is a versatile multicopper oxidase that holds great promise for many biotechnological applications. For such applications, it is essential to explore good biocatalytic systems for high activity and recyclability. The feasibility of membrane enclosed enzymatic catalysis (MEEC) for enzyme recycling with laccase was evaluated. The dialysis membrane enclosed laccase catalysis (DMELC) was tested for the conversion of the non-phenolic model substrate 2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS). Trametes versicolor laccase was found to be completely retained by the dialysis membrane during the process. The ABTS total conversion after DMELC reached the same values as the batch reaction of the enzyme in solution. The efficiency of DMELC conversion of ABTS under different process conditions including shaking speed, temperature, ABTS concentration and pH was investigated. The repetitive dialysis minimally affected the activity and the protein content of the enclosed laccase. DMELC retained 70.3 ± 0.8% of its initial conversion after 5 cycles. The usefulness of MEEC extends to other enzymes with the benefit of superior activity of an enzyme in solution and the recyclability which is normally only obtained with immobilized enzymes.

Proximity ligation assay induced and DNAzyme powered DNA motor for fluorescent detection of thrombin.

A novel DNA motor for thrombin detection was described here based on proximity ligation assay (PLA) induced DNAzyme recycling cleavage. Fluorophore labeled DNA is modified on gold nanoparticles (AuNPs) and the fluorescent signal is quenched by AuNPs. The PLA between target thrombin and two aptamers induces the forming of Mg2+-dependent DNAzyme. The fluorophore labeled DNA is cleaved circularly by the DNAzyme, releasing the fluorescent fragment from AuNPs surface. The cleavage and rebinding process create a processive walking along AuNPs surface track. As a result, the fluorescent intensity recovers significantly. A good linear relationship is obtained between the ratio of fluorescence intensity and thrombin concentration in the range from 10 pM to 10 nM. The limit of detection is calculated to be 4 pM. These results are comparable or even better than other amplification based methods.

A catalytic cleavage strategy for fluorometric determination of Hg(II) based on the use of a Mg(II)-dependent split DNAzyme and hairpins conjugated to gold nanoparticles.

A catalytic cleavage strategy was developed for the fluorometric determination of Hg(II). The method is based on the use of a Mg(II)-dependent split DNAzyme. Fluorophore labeled hairpins were conjugated to gold nanoparticles (AuNPs) upon which fluorescence is quenched. Thymine-Hg(II)-thymine (T-Hg(II)-T) interaction causes the two DNA sequences to form an entire enzyme-strand DNA (E-DNA). The E-DNA bind to the hairpins on the AuNPs to form a Mg(II)-dependent DNAzyme structure. The circular cleavage of hairpins results in a signal amplification and in the recovery of fluorescence. The assay has a limit of detection (LOD) as low as 80 pM of Hg(II). This LOD is comparable to those obtained with other amplification strategies. The method was successfully applied to the determination of Hg(II) in Chinese herbs (Atractylodes macrocephala Koidz). Graphical abstract Schematic of a catalytic cleavage strategy based on Mg(II)-dependent split DNAzyme for fluorometric determination of Hg(II).