Hybrid functional electronic structure of PbPdO?, a small-gap semiconductor

PbPdO?, a ternary compound containing the lone pair active ion Pb2? and the square planar d?Pd2? ion, has attracted recent interest because of the suggestion that its electronic structure, calculated within density functional theory using either the local density or the generalized gradient approximation, displays zero-gap behavior. In light of the potential ease of doping magnetic ions in this structure, it has been suggested that the introduction of spin, in conjunction with zero band gap, can result in unusual magnetic ground states and unusual magnetotransport. It is known that most electronic structure calculations do not properly obtain a band gap even for the simple oxide PdO, and instead obtain a metal or a zero-gap semiconductor. Here we present density functional calculations employing a screened hybrid functional which correctly obtain a band gap for the electronic structure of PdO. When employed to calculate the electronic ground state of PbPdO?, a band gap is again obtained, which is consistent with both the experimental data on this compound, as well as a consideration of valence states and of metal-oxygen connectivity in the crystal structure. We also present comparisons of the absolute positions (relative to the vacuum level) of the conduction band minima and the valence band maxima in α-PbO, PdO and PbPdO?, which suggest ease of p-type doping in PbPdO?, that has been observed even in nominally pure materials.     

Study on synthesis and evolution of sodium potassium niobate ceramic powders by an oxalic acid-based sol–gel method

Potassium sodium niobate (KNN) ceramic powders by a variation of sol–gel method is synthesized. The metal precursors used for the KNN synthesis are potassium carbonate, sodium carbonate and niobium hydroxide, ethylene glycol are used as chelating and esterification agent, respectively. The effects of amount of oxalic acid (OA) and ethylene glycol (EG), pH value on the stability of the precursor sol were investigated. The evolution of (K_0.5Na_0.5)NbO₃ crystal phase was also investigated by XRD, IR, SEM and TG-DTA. The results showed that stable precursor sol was formed when n_(OA):n_(Mn+) = 3:1, n_(OA):n_(EG) = 1:2 and pH value was in the range of 2.5–3.5. Xerogel was sintered in the range of 500–650 °C to prepare K₆Nb_10.88O₃₀ and Na₂Nb₄O₁₁ powder. Then the compound was sintered at 750 °C to produce perovskite (K_0.5Na_0.5)NbO₃ ceramic powders. The grain size is about 100–200 nm.     

Meandering Spiral Waves Induced by Time-Periodic Coupling Strength

Effects of time-periodic coupling strength (TPCS) on spiral waves dynamics are studied by numerical computations and mathematical analyses. We find that meandering or drifting spirals waves, which are not observed for the case of constant coupling strength, can be induced by TPCS. In particular, a transition between outward petal and inward petal meandering spirals is observed when the period of TPCS is varied. These two types of meandering spirals are separated by a drifting spiral, which can be induced by TPCS when the period of TPCS is very close to that of rigidly rotating spiral. Similar results can be obtained if the coupling strength is modulated by a rectangle wave. Furthermore, a kinetic model for spiral movement suggested by Di et al., [Phys. Rev. E 85 (2012) 046216] is applied for explaining the above findings. The theoretical results are in good qualitative agreement with numerical simulations.     

Synthesis and Crystal Structure of a Rubidium Lanthanum Borate Rb3La3（BO3）4

The title compound was obtained by the flux method and its structure was determined. It crystallizes in monoclinic, space group P2/c with a = 11.0024（17）, b = 9.2979（14）, c = 14.500（2） A, β = 110.879（2）°, V = 1385.9（4） A^3, Z = 4, Mr= 908.38, F（000） = 1592, p = 19.601 mm^-1, Dc = 4.353 g/cm^3, the final R = 0.0481 and wR = 0.1257 for 2532 observed reflections with I 〉 2σ（I）, The Rb3La3（BO3）4 structure can be viewed as a 3-dimensional scaffold-like framework constructed by La-O polyhedra and BO3 groups. Two Rb＋ ions locate in a channel along the a direction and the rest one in a cavity.     

Effects of Coupling Distance on Synchronization and Coherence in Chaotic Neural Networks

Effects of coupling distance on synchronization and coherence of chaotic neurons in complex networks are numerically investigated. We find that it is not beneficial to neurons synchronization if confining the coupling distance of random edges to a limit dmax, but help to improve their coherence. Moreover, there is an optimal value of dmax at which the coherence is maximum.     

Microwave Absorption and Response Modeling of Nanocomposites Embedded SiC Nanoparticles

We study the mechanism of microwave response properties of SiCv/paraffin nanocomposites and propose a mi- crowave absorption model of nanocomposites based on the conservation law of energy and the theory of electro- magnetic scattering. Using the model we calculate the reflectivity of SiCp/paraffin nanocomposites ranging from 2 GHz to 18 GHz. The calculated results are very consistent with the experimental data in the frequency range investigated.     

Preparation and Ferroelectric Properties of Double-Scale PZT Composite Piezoelectric Thick Film

Dense and crack-free double-scale lead zirconate titanate （Pb（Zr0.52 Ti0.48 ）O3, PZT） composite piezoelectric thick films have been successfully fabricated on Au/Cr/SiO2/Si substrates by a modified sol-gel method. The XRD analysis indicates that the thick film possesses a single-phase perovskite-type structure. The SEM micrograph shows that the surface is crack-free and the cross section is dense and dear. The thickness of the PZT thick film is about 4 μm. It also exhibits good ferroelectric properties, and has high direct current compression resistant properties. At the test frequency of 1 kHz, the film has the coercive field of 50 kV/cm, the saturation polarization of 54μC/cm^2 and the remnant polarization of 30 μC/cm^2.     

固相萃取-气相色谱-质谱联用测定葱属蔬菜中二甲嘧菌胺和吡氟禾草灵残留量

在固相萃取基础上通过极性区间排列净化前处理,建立了固相萃取-气相色谱-质谱法检测青葱、大葱、洋葱中的二甲嘧菌胺与吡氟禾草灵残留的分析方法。 样品用乙腈提取,加入氯化钠继续均质,离心分层后取部分乙腈层过Envi-18柱和Florisil柱净化后上机测试。 采用选择离子扫描方式,外标法定量。 分析方法简便、快速。 通过优化前处理和上机条件,在最优条件下进行测试,二甲嘧菌胺与吡氟禾草灵的定量下限(S/N=10)均小于0.01 mg/kg,在加标水平0.01～0.2 mg/kg范围内,回收率分别为81.4％～94.6％、107％～129％,相对标准偏差分别为3.3％～11％、4.0％～9.7％。     

A new approach of joint trajectories for cartesian path approximation of mechanical manipulators

Summary The path planning of the industrial robots is usually done in joint space to reduce the on-line computational amount. To do this, a sequence of Cartesian knots chosen carefully must be transformed into joint space. The joint trajectories are often interpolated by polynomial functions, usually by cubic splines. This paper presents a new method for joint trajectories approximation. The method requires to transform the positions, velocities and accelerations of the knots. It can reduce the number of needed points and consequently the total computational amount, and can realize the joint trajectories in real-time. A comparison to the usual cubic spline approach is shown by an illustrative example.

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Sommario La programmazione delle traiettorie Cartesiane dei robots industriali è fatta spesso nello spazio dei giunti per ridurre la quantità di calcolo on-line. Per fare questo, una sequenza di punti Cartesiani scelti attentamente deve essere trasformata nello spazio dei giunti. Le traiettorie dei giunti vengono interpolate dalle funzioni polinomiali, quasi sempre da splines cubici. Questo lavoro presenta un nuovo metodo per approssimare le traiettorie dei giunti; il metodo richiede di trasformare le posizioni, le velocità e le accelerazioni dei punti Cartesiani. Il metodo può ridurre il numero dei punti scelti e di conseguenza la quantità di calcolo totale, e può realizzare le traiettorie dei giunti in tempo reale. Un confronto con l'approccio di splines cubici è illustrato da un'esempio semplice.

     

铅铈和铅钙锡合金阳极腐蚀膜的性能研究

利用叠加交流伏安法、线性电位扫描法、交流阻抗技术和XPS研究了铅铈合金和铅钙锡合金在阳极1.28 V, 4.5 mol/L的硫酸溶液中所形成的阳极腐蚀膜. 结果表明: 稀土铈能抑制阳极膜中高阻抗的Pb(II)化合物的生长, 降低腐蚀膜的阻抗, 并增加膜的孔隙率. 同时可以提高合金的析氢过电位, 有利于电池免维护性能的提高.