Colloidal crystal layers of hexagonal nanoplates by convective assembly

Particles of the zeolite ZSM-2 prepared as nearly hexagonal nanoplatelets were coated onto flat substrates by a convective assembly technique. On the submillimeter scale, coatings ranged in patterns from striped to continuous. Particles were preferentially oriented out-of-plane, as supported by X-ray diffractometry. The novel observation is that where the particle coating was only a monolayer thick, particles were locally close-packed and uniformly oriented both in and out of plane in a hexagonal colloidal crystalline arrangement that may be described as being tiled (observations by scanning electron microscopy). This is the first documented demonstration of convective assembly applied to anisometric nanoparticles that resulted in particulate coatings with locally ordered microstructure, i.e., colloidal crystallinity.     

Synthesis of 3,5-ditert-butyl-4-hydroxybenzoates and their thermal antioxidation behavior for polypropylene

Butyl 3,5-ditert-butyl-4-hydroxybenzoate (BB), octyl 3,5-ditert-butyl-4-hydroxybenzoate (OB), and dodecyl 3,5-ditert-butyl-4-hydroxybenzoate (DB) were synthesized and characterized, and their performance as antioxidant for polypropylene (PP) were also investigated. The thermooxidative stability of PP with different antioxidants were assessed by the measurements of long-term accelerated aging, differential scanning calorimetery, and thermogravimetric analysis. The results showed that 3,5-ditert-butyl-4-hydroxybenzoates could effectively inhibit the oxidation degradation of PP. And it was also found that the antioxidant efficiency of BB, OB, and DB for PP was in the order of DB > OB > BB.     

再生纤维素荧光膜

由纤维素铜氨溶液与钒磷酸钇：铕，铝酸钡镁；铕，硫化锌镉：铜和硅酸锌：锰荧光粉混合分别制备了４种再生纤维素荧光膜，研究了这些膜的荧光光谱，相对荧光强度，结晶度及力学性能变化。实验结果表明当添加５％荧光粉时，含钒磷酸钇：铕，铝酸钡镁：铕和硫化锌镉：铜的膜仍保持光粉的结晶峰，在紫外光照射下分别发出红，蓝，黄荧光，其相对荧光强度依次为８１％，７９％及７４％。当膜含５％硅酸锌：锰时，在紫外光照射下发射微弱的     

The role of fluid flow and convective steering during the assembly of colloidal crystals

Three-dimensional computations of steady flows directed toward the (1 1 1) plane of a face-centered cubic (fcc) packing of spheres are carried out to assess the convective steering hypothesis, which posits that solvent flow could play a role in the assembly of colloidal crystals. The computations clearly show the kinematics of flows into and through the packing and clarify the influences of fluid inertia and particle arrangement. Results from the computations accurately describe the outcome of macroscopic experiments and are consistent with a network model applied to the microscopic, colloidal system. For the geometry considered here, flows are predicted to direct over 20% more fluid into selected positions along the surface of the packing and reinforce the tendency for ordering newly growing layers with fcc symmetry.     

Photocatalytic photodegradation of xanthate over C, N, S-tridoped TiO2 nanotubes under visible light irradiation

C, N, S-tridoped TiO₂ nanotubes were synthesized via hydrothermal synthesis and post-treatment, and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), the Brunauer-Emmett-Teller method (BET), and UV-vis diffuse reflectance spectroscopy (DRS). The UV-diffuse reflectance spectra of all the C, N, S-tridoped TiO₂ nanotubes greatly extended the absorption edge to the visible light region, and the absorbance in the visible region increased with increasing molar ratio of thiourea to Ti (R), which could be attributed to C, N, S-tridoping in the form of cation C-doping, interstitial N-doping, cation S-doping, and adsorbed ions’ states. The photocatalytic activity of C, N, S-tridoped TiO₂ nanotubes was evaluated by photocatalytic photodegradation of potassium ethyl xanthate (KEX) under visible light irradiation. It was found that the photocatalytic activity of the prepared samples increased with increasing molar ratio of thiourea to Ti (R). At R=6, the photocatalytic activity of the tridoped sample TNTS-6 reached a maximum value. With further increase in R, photocatalytic activity of the sample decreased, which could be attributed to the high visible light activity resulting from the balance between visible light absorption and recombination of electron/hole pairs.     

Oxygen isotope homogeneity assessment for apatite U-Th-Pb geochronology reference materials

Secondary ion mass spectrometry (SIMS) measurement of oxygen isotopes in apatite has been employed more and more in petrogenetic, metallogenic, and climate change studies. Well-characterised reference materials are needed due to the matrix effect, but they are yet to be well established. In this study, we conducted in-situ oxygen isotopic and chemical analyses on six commonly used apatite reference materials (ie, Emerald, Kovdor, McClure, Mud Tank, Otter Lake, and Slyudyanka) and two in-house apatite references (Qinghu and GEMS 203) to assess their oxygen isotope homogeneity and applicability for microbeam analyses. Our results show that all these apatite references are in general chemically homogeneous. In terms of oxygen isotopes, GEMS 203 (δ¹⁸O = 9.85 ± 0.40‰ [2SD], corrected by Durango 3), Kovdor (δ¹⁸O = 6.55 ± 0.38‰, 2SD), and McClure (δ¹⁸O = 5.94 ± 0.42‰, 2SD) are fairly homogeneous, whereas Emerald (δ¹⁸O = 10.37 ± 0.45‰, 2SD), Mud Tank (δ¹⁸O = 6.35 ± 0.46‰, 2SD), Otter Lake (δ¹⁸O = 9.71 ± 0.47‰, 2SD), Qinghu (δ¹⁸O = 5.44 ± 0.49‰, 2SD), and Slyudyanka (δ¹⁸O = 17.49 ± 0.43‰, 2SD) are less homogenous. This indicates that the former group represents better reference materials for in-situ oxygen isotopic analyses, whilst the latter group can be used as secondary reference material for analytical quality control.     

Existence results for boundary value problems of high order differential equations involving Caputo derivative

We study boundary value problems for differential equations involving Caputo derivative of order ????(n?1,n) in Banach spaces. Existence and uniqueness results of solutions are established by virtue of the H?lder??s inequality, a suitable singular Gronwall??s inequality and fixed point theorem via a priori estimate method. At last, three examples are given to illustrate the results.     

An efficient algorithm for maximal margin clustering

Maximal margin based frameworks have emerged as a powerful tool for supervised learning. The extension of these ideas to the unsupervised case, however, is problematic since the underlying optimization entails a discrete component. In this paper, we first study the computational complexity of maximal hard margin clustering and show that the hard margin clustering problem can be precisely solved in O(n ^d+2) time where n is the number of the data points and d is the dimensionality of the input data. However, since it is well known that many datasets commonly ‘express’ themselves primarily in far fewer dimensions, our interest is in evaluating if a careful use of dimensionality reduction can lead to practical and effective algorithms. We build upon these observations and propose a new algorithm that gradually increases the number of features used in the separation model in each iteration, and analyze the convergence properties of this scheme. We report on promising numerical experiments based on a ‘truncated’ version of this approach. Our experiments indicate that for a variety of datasets, good solutions equivalent to those from other existing techniques can be obtained in significantly less time.