From β-Na2B6O10 to Na3AlB8O15 and Na3Al2B7O15: Structural Tuning of Anionic-Group Architectures by Substitution of [BO4] by [AlO4] Covalent Tetrahedra

Two new sodium aluminum borates, Na₃AlB₈O₁₅ and Na₃Al₂B₇O₁₅, have been successfully synthesized by the high-temperature solution method. They crystallize in the different space groups, P2₁/c and P2/c, respectively. The B−O configurations of β-Na₂B₆O₁₀, Na₃AlB₈O₁₅ and Na₃Al₂B₇O₁₅ are compared to feature complicated different dimensional open-framework structures caused by the substitution of [BO₄] by [AlO₄] covalent tetrahedra. Moreover, the experimental results indicate that Na₃AlB₈O₁₅ and Na₃Al₂B₇O₁₅ have short ultraviolet (UV) cutoff edges (<187 nm). The first-principles calculations show that Na₃AlB₈O₁₅ and Na₃Al₂B₇O₁₅ have moderate birefringence (0.075 and 0.041@1064 nm, respectively).     

Bogdanov–Takens bifurcation in an oscillator with negative damping and delayed position feedback

In this paper, Bogdanov–Takens bifurcation occurring in an oscillator with negative damping and delayed position feedback is investigated. By using center manifold reduction and normal form theory, dynamical classification near Bogdanov–Takens point can be completely figured out in terms of the second and third derivatives of delayed feedback term evaluated at the zero equilibrium. The obtained normal form and numerical simulations show that multistability, heteroclinic orbits, stable double homoclinic orbits, large amplitude periodic oscillation, and subcritical Hopf bifurcation occur in an oscillator with negative damping and delayed position feedback. The results indicate that negative damping and delayed position feedback can make the system produce more complicated dynamics.     

Totally real conformal minimal tori in the hyperquadric Q 2

Our purpose is to study the minimal tori in the hyperquadric Q ₂. Firstly, we obtain a necessary and sufficient condition for the minimal surface in Qn which is also minimal in CP ⁿ⁺¹. Next, we show that this kind of minimal surface (neither holomorphic nor anti-holomorphic) with constant curvature in Q ₂ is part of a flat totally real torus. Finally, we prove that totally real minimal flat tori in Q ₂ must be totally geodesic, and we classify all the totally geodesic closed surfaces in Q ₂.     

单摆作谐振动的最大摆角的分析

本文根据实验上的微小偏差准则和试验中的最小可分辨时间来确定单摆作谐振动时的最大摆角     

1-Aminoxymethylcyclopropanecarboxylic acid as building block of β N-O turn and helix: synthesis and conformational analysis in solution and in the solid state

Cyclopropane side-chained β^2,2-aminoxy oligopeptides were synthesized and conformationally studied. β N-O turn in solution and β N-O helix in the solid state was characterized by ¹H NMR, 2D NOESY and FT-IR as well as X-ray crystallography studies. Almost no changes has been observed with the disturbance at α carbon bond angle compared with dimethyl substituted one. This study provided the opportunity to design the bioactive peptidomimetics in a more elaborate way.     

Magnetic solid‐phase extraction for determination of sulpiride in human urine and blood using high‐performance liquid chromatography

A novel and efficient sample preconcentration technique based on the Fe₃O₄ magnetic nanoparticles (Fe₃O₄ MNPs) coated with silica (SiO₂) has been developed for extraction and determination of sulpiride. The functionalized MNPs showed excellent dispersibility in aqueous solution and were applied to magnetic solid‐phase extraction of sulpiride from human urine and blood prior to high‐performance liquid chromatography analysis. The separation, preconcentration and desorption procedure was completed in 10 min. Optimal experimental conditions, including sample pH, the amount of the MNPs, eluent type and volume, and the ultrasonication time were studied and established. The method showed good linearity for the determination of sulpiride in the concentration range of 10–1000 ng/mL in urine and blood. The recovery of the method was in the range between 91.2 and 97.5%, and the limit of detection was 2 ng/mL for sulpiride in human blood and urine. The results indicated that the present procedure is a suitable pretreatment method for biological samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Discrete element modeling on the crack evolution behavior of brittle sandstone containing three fissures under uniaxial compression

Based on experimental results of brittle, intact sandstone under uniaxial compression, the micro-parameters were firstly confirmed by adopting particle flow code(PFC2D). Then, the validation of the simulated models were cross checked with the experimental results of brittle sandstone containing three parallel fissures under uniaxial compression. The simulated results agreed very well with the experimental results, including the peak strength, peak axial strain, and ultimate failure mode. Using the same microparameters, the numerical models containing a new geometry of three fissures are constructed to investigate the fissure angle on the fracture mechanical behavior of brittle sandstone under uniaxial compression. The strength and deformation parameters of brittle sandstone containing new three fissures are dependent to the fissure angle. With the increase of the fissure angle, the elastic modulus, the crack damage threshold,and the peak strength of brittle sandstone containing three fissures firstly increase and secondly decrease. But the peak axial strain is nonlinearly related to the fissure angle. In the entire process of deformation, the crack initiation and propagation behavior of brittle sandstone containing three fissures under uniaxial compression are investigated with respect tothe fissure angle. Six different crack coalescence modes are identified for brittle sandstone containing three fissures under uniaxial compression. The influence of the fissure angle on the length of crack propagation and crack coalescence stress is evaluated. These investigated conclusions are very important for ensuring the stability and safety of rock engineering with intermittent structures.