A retractable structure based on Bricard linkages and rotating rings of tetrahedra

Retractable structures which alter their geometries according to practical requirements are widely used in roof structures of stadiums for their versatility. A retractable structure based on threefold-symmetric Bricard linkages and rotating rings of tetrahedra is proposed and developed in this paper. By replacing each link of a threefold-symmetric Bricard linkage with a tetrahedron, a retractable structure is obtained which can repeatedly open and close by rotating the tetrahedra. The geometric relationship between the retractable structure and the threefold-symmetric Bricard linkage is derived and ranges of main geometric parameters are determined to ensure a continuous and smooth movement in the deployment of the structure. Then the relative displacement of the support and the open rate of the structure, two main parameters concerned in practical applications, are investigated. Preferred ranges of main geometric parameters are proposed and a physical model is manufactured to verify them. A discussion on some possible improvements and modifications of the structure is also presented.     

Synthesis and characterization of wholly aromatic poly(azomethine)s containing donor–acceptor triphenylamine moieties

N‐(4‐nitrophenyl)‐4′,4″‐bisformyl‐diphenylamine was synthesized from N‐(4‐nitrophenyl)‐diphenylamine by the Vilsmeier‐Haack reaction. Soluble aromatic poly(azomethine)s (PAMs) were prepared by the solution polycondensation of N‐(4‐nitrophenyl)‐4′,4″‐bisformyl‐diphenylamine and aromatic diamine in N‐methyl‐2‐pyrrolidone (NMP) at room temperature under reduced pressure. All the PAMs are highly soluble in various organic solvents, such as N,N‐dimethylacetamide (DMAc), chloroform (CHCl₃), and tetrahydrofuran (THF). Differential scanning calorimetry (DSC) indicated that these PAMs had glass‐transition temperatures (T_gs) in the range of 170–230 °C, and a 10% weight‐loss temperatures in excess of 490 °C with char yield at 800 °C in nitrogen higher than 60%. These PAMs in NMP solution showed UV‐Vis charge‐transfer (CT) absorption at 405–421 nm and photoluminescence peaks around 462–466 nm with fluorescence quantum efficiency (Φ_F) 0.10–0.99%. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of these PAMs can be determined from cyclic voltammograms as 4.86–5.43 and 3.31–3.34 eV, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4921–4932, 2007     

Metal complexes of 2-hetarylindandiones-1,3

The chelate and molecular complexes of 2-(2-benzazolyl, perimidyl)-indandiones-1,3 were synthesized for the first time. The structures of the ligands (tautomeric forms) and complex compounds were determined from the X-ray diffraction, ¹H, ¹³C NMR, and IR data and the quantum-chemical calculations (RHF SCF in 6-31 G** basis).     

Simulation of interaction between a rarefied gas jet and an obstacle by the methods of molecular dynamics

An efficient method of direct numerical simulation is proposed. The steady-state flow field generated by the impingement of a gas jet on a wall is studied as an example. The numerical results obtained during this study are in good agreement with the numerical solutions of other authors.     

Electrochemical synthesis of niobium compounds in anodic dissolution of ferroniobium in methanol

Anodic dissolution of ferroniobium in anhydrous methanol in the presence of sodium methylate was studied. The possibility of recovering pure hexamethoxyniobate from the electrolyzate and its conversion into niobium methylate with an iron content not exceeding 0.01% was analyzed.     

Synthesis and structure of unsymmetrical cross-conjugated dienones with thienyl substituents

By condensation of thiophenecarbaldehyde and m-nitrobenzaldehyde with furyl-, thienylmethylenecyclohexanones in basic medium 2-(het)arylmethylene-6-thienylmethylenecyclohexanones were prepared. Under the conditions of acid catalysis analogously built dienones were synthesized containing 5-nitrothiophene fragment. Based on the data of IR and ¹H NMR spectroscopy their E,E-configuration was established.     

Target Level Method in Linear Multi-Criterion Problems

We consider the target level method for solving linear multi-criterion maximization problems. The method finds an efficient (Pareto-optimal) vector estimate that is closest in the Chebyshev metric to the target level point specified by the decision maker. The proposed method describes (parametrizes and approximates) the efficient set. In the linear case the number of scalar optimization problems needed to describe the set of efficient vector estimates is substantially reduced. A formula is derived which, under certain conditions, can be used to compute efficient vector estimates without solving any optimization problems. An algorithm based on these results is proposed for two-criterion problems.     

椭圆偏振光实验鉴定的新方法

1用λ/4波片和检偏器鉴定椭圆偏振光存在的缺点 鉴定椭圆偏振光常用的方法是先用检偏器鉴定椭圆偏振光长短轴的方位,再用λ/4波片使之转化成线偏振光,然后用检偏器找到消光位置.     

Excitation Cross Section for Resonance Transitions of Rhenium Atoms Excited by Slow Electrons

Excitation of rhenium atoms by electron impact is investigated by the method of extended crossing beams. At electron energies of 50 eV, the excitation cross sections of 36 resonance and competing transitions in ReI are measured. Within the energy range from the threshold value to 250 eV, six optical excitation functions are detected. The reliability of data on transition probabilities in ReI has been analyzed.