Manipulating the electronic structures of silicon carbide nanotubes by selected hydrogenation

We show that the electronic and atomic structures of silicon carbide nanotubes (SiCNTs) undergo dramatic changes with hydrogenation from first-principles calculations based on density-functional theory. The exo-hydrogenation of a single C atom results in acceptor states close to the highest occupied valence band of pristine SiCNT, whereas donor states close to the lowest unoccupied conduction band appear as a Si atom being hydrogenated. Upon fully hydrogenating Si atoms, (8,0) and (6,6) SiCNTs become metallic with very high density of states at the Fermi level. The full hydrogenation of C atoms, on the other hand, increases the band gap to 2.6 eV for (8,0) SiCNT and decreases the band gap to 1.47 eV for (6,6) SiCNT, respectively. The band gap of SiCNTs can also be greatly increased through the hydrogenation of all the atoms.     

环己烷催化氧化制取顺酐和醋酸的催化剂研究

为研究气态环己烷催化氧化制取顺酐及醋酸的新反应，采取不同的方法制备了系列固体VPO催化剂.借助XRD、FT-IR对催化剂进行了主体晶相确定，用氧化还原滴定方法测定了不同晶相催化剂中钒的平均氧化数.结合催化反应的活性评价，发现催化剂主体晶相、结晶度、活化气氛和催化剂的V4＋/V5＋比均对目标反应的催化活性产生影响，5种催化剂中以(VO)2P2O7晶相催化剂的活性为最高.     

A combinatorial approach to study solvent-induced self-assembly of mixed poly(methyl methacrylate)/polystyrene brushes on planar silica substrates: effect of relative grafting density

This article reports the study of the effect of relative grafting densities of two polymer chains on solvent-induced self-assembly of mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes through a combinatorial approach. Gradient-mixed PMMA/PS brushes were synthesized from a gradient-mixed initiator-terminated monolayer by combining atom transfer radical polymerization (ATRP) and nitroxide mediated radical polymerization (NMRP) in a two-step process. The gradient-mixed initiator-terminated monolayer was fabricated by first formation of a gradient in density of an ATRP initiator through vapor diffusion followed by backfilling of an NMRP-initiator-terminated trichlorosilane. After treatment of a gradient-mixed brush whose PS Mn was slightly lower than that of PMMA with glacial acetic acid, a selective solvent for PMMA, relatively ordered nanodomains were observed in the region where the ratio of PS to PMMA grafting density (number of polymer chains/nm2) was in the range from 0.67 to 2.17 and the overall grafting density was approximately 0.85 polymer chains/nm2. Contact angle hysteresis were high (> or =40 degrees ) in this region and XPS studies confirmed that the PMMA chains were enriched at the outermost layer. The nanodomains are speculated to be of a micellar structure with PS chains forming the core shielded by PMMA chains.     

Structural and physical properties of the 6H BaRuO3 polymorph synthesized under high pressure

The single-phase 6H BaRuO₃ with the hexagonal BaTiO₃ structure was synthesized at 5 GPa and 1000 °C. Rietveld refinement of the powder X-ray data for the 6H phase resulted in the lattice parameters to be a=5.7127(1) Å and c=14.0499(2) Å; the average Ru-O distance and direct Ru-Ru distance in the Ru₂O₉ dioctahedron being 1.992(6) and 2.5658(14) Å, respectively. The electrical resistivity of the 6H BaRuO₃ follows a relationship of ρ versus T^3/2 below 60.0 K, a signature deviation from the Fermi-liquid behavior. Both magnetic susceptibility and specific heat data indicate that the 6H BaRuO₃ is an exchange-enhanced Pauli paramagnet due to the electron correlation effect with large Wilson ratio R_W and Stoner enhancement factor. The comprehensive evolution of transport and magnetic properties from 9R across 4H to 6H BaRuO₃ was discussed.     

有限群极大子群的θ-子群偶

N.P.Mukherjee和 P.Bhattacharya在“On theta pairs for a maximal sub-group”(Proc.Amer.Math.Soc,Vl09N3(1990))一文中定义了有限群的极大子群的θ-子群偶概念,研究了极大子群的极大θ-子群偶对群结构的影响,得到了一系列结果.本文在进一步探究θ-子群偶性质的基础上,对该文中一系列主要结果作出了本质性的改进,并给出了可解性、幂零性的一些新刻划.     

IMPACT MODEL RESOLUTION ON PAINLEVE’S PARADOX

Painlevé‘s paradox is one of the basic difficulties for solving LCP of dynamic systems subjected to unilateral constraints. A bi-nonlinear parameterized impact model, consistent with dynamic principles and experimental results, is established on the localized and quasi-static impact model theory. Numerical simulations are carried out on the dynamic motion of Painlevé‘s example. The results confirm ““““impact without collision““““ in the inconsistent states of the system. A ““““critical normal force““““ which brings an important effect on the future movement of the system in the indeterminate states is found. After the motion pattern for the impact process is obtained from numerical results, a rule of the velocity‘s jump that incorporates the tangential impact process is deduced by using an approximate impulse theory and the coefficient of restitution defined by Stronge. The results of the jump rule are quite precise if the system rigidity is big enough.     

Magnetic Properties of Pt-Based Nanoalloys: A Critical Review

In recent years, magnetic nanoalloys (MNAs) have attracted many attentions from all over the world, due to their potential applications in the broad fields of magneto-optics, data storage, engineering, and biology. Among these MNAs, Pt–M (M = Fe, Co, Ni) MNAs have been considered to be the most promising ones, due to their superparamagnetism and response to a magnetic field. Here, we firstly review the experimental work on the synthesis, characterization, and magnetic properties of Pt–Fe, Pt–Co, and Pt–Ni MNAs. Then, we discuss the recent theoretical work on Pt–Fe, Pt–Co, and Pt–Ni MNAs. Moreover, we also review the main applications of Pt–Fe, Pt–Co, and Pt–Ni MNAs in the fields of biology, information storage, and magnetic separation. It is found that the size, shape, and composition of Pt–Fe, Pt–Co, and Pt–Ni MNAs play a critical role on their fundamental magnetic properties from both the experimental and theoretical points of view. It is expected that this review could be a valuable resource for both experimental and theoretical researchers, who are interested in Pt-based MNAs.     

Enhanced slow light propagation in photonic crystal waveguides using angular properties of scatter elements

Applicability of the angular properties of scatter elements as a tool to achieve improved slow light performance with small group velocity dispersion and large bandwidth in photonic crystal waveguides is investigated. A polyatomic photonic crystal waveguide, including two scatter elements with different geometrical shapes in each primitive cell, is proposed to investigate the feasibility of our method. Numerical results show that a versatile control of the dispersion relation of slow light modes, with large normalized delay-bandwidth products ranging from 0.2085 to 0.3394, can be obtained using a unique geometrical parameter.     

Notable shift of ultraviolet intensity on Sn-doped ZnO nanostructure fabricated by sol–gel method

Sn-doped ZnO (SZO) thin films are deposited by sol–gel dip-coating method with Sn content at 0 at.% and 1–15 at.% with an increment of 2 at.%. The structure and luminescence of the films are investigated. X-ray diffraction results indicate that all the SZO samples show preferential orientation along the (002) direction, and the scanning electron microscope exhibits that the surface morphology of the films change from nanoparticles to nanorods with increasing Sn concentration. X-ray photoelectron spectroscopy reveals that Sn exists as valence of +4 in the matrix. The photoluminescence peaks at 381 and 398 nm are observed in all the samples. The ratio of intensity of peak at 381 nm to that of peak at 398 nm differed markedly. The intensity of peak at 398 nm might be due to the response for the Sn atoms, while the intensity of peak at 381 nm is probably related to the quantum size effect.