Theoretical insights on a series of difluoramino group–based energetic molecules

A series of difluoramino group–based energetic molecules was designed and the relative properties were investigated by density functional theory. The results show that all the designed molecules have high positive heat of formation which ranges from 479.48 to 724.02 kJ/mol, detonation velocity ranges from 8.01 to 11.26 km/s, detonation pressure ranges from 28.03 to 63.46 GPa, and impact sensitivity ranges from 18.2 to 54.5 cm. Then, compounds D2, D3, D5, E4, E5, E6, and F2 were selected as the potential high energy density materials based on detonation properties and sensitivities. Natural bond orbital charges, electronic density, frontier molecular orbital, electrostatic potential on the surface, and thermal dynamic parameters of the screened molecules (compounds D2, D3, D5, E4, E5, E6, and F2) were also predicted at B3LYP/6‐31G(d,p) level to give a better understanding on the chemical and physical properties of them.     

Comparison of linear system solvers applied to diffusion-type finite element equations

Summary Various iterative methods for solving the linear systems associated with finite element approximations to self-adjoint elliptic differential operators are compared based on their performance on serial and parallel machines. The methods studied are all preconditioned conjugate gradient methods, differing only in the choice of preconditioner. The preconditioners considered arise from diagonal scaling, incomplete Cholesky decomposition, hierarchical basis functions, and a Neumann-Dirichlet domain decomposition technique. The hierarchical basis function idea is shown to be especially effective on both serial and parallel architectures.This work was supported by the Applied Mathematical Sciences Program of the US Department of Energy under contract DE-AC02-76ER03077     

Synthesis and Characterization of a Novel Degradable Aliphatic Polyester that Contains Monomeric Lactate Sequences

Summary: A novel degradable aliphatic polyester that contains monomeric lactate sequences is synthesized via melt‐polycondensation of ethylene glycol lactate diol (EGLD) with succinic anhydride without the use of catalyst. The structure of the EGLD precursor and the polyester are verified with FT‐IR and ¹H NMR spectra. Gel permeation chromatography reveals that the weight‐average molecular weight of the polyester is 5.5 × 10⁴ with a polydispersity index (PDI) of 1.7. Differential scanning calorimetry profiles reveal that the polyester is a semicrystalline polymer with a glass transition temperature of −12 °C and melting temperature of 101 °C. The weight loss percentage of the polyester after immersing for 208 d in active sludge is 2.7%, which suggests degradation has occurred.

The synthesis route of the polyester synthesized here (see inset for structure).     

Dynamic stability of the three‐dimensional axisymmetric Navier‐Stokes equations with swirl

In this paper, we study the dynamic stability of the three‐dimensional axisymmetric Navier‐Stokes Equations with swirl. To this purpose, we propose a new one‐dimensional model that approximates the Navier‐Stokes equations along the symmetry axis. An important property of this one‐dimensional model is that one can construct from its solutions a family of exact solutions of the three‐dimensionaFinal Navier‐Stokes equations. The nonlinear structure of the one‐dimensional model has some very interesting properties. On one hand, it can lead to tremendous dynamic growth of the solution within a short time. On the other hand, it has a surprising dynamic depletion mechanism that prevents the solution from blowing up in finite time. By exploiting this special nonlinear structure, we prove the global regularity of the three‐dimensional Navier‐Stokes equations for a family of initial data, whose solutions can lead to large dynamic growth, but yet have global smooth solutions. © 2007 Wiley Periodicals, Inc.     

超高效液相色谱-串联质谱法检测畜产品和水产品中3-甲基喹恶啉-2-羧酸残留

以猪肉、猪肝、猪肾、胖头鱼、对虾和蟹为试验材料,建立了喹乙醇(OLA)的残留标示物3-甲基喹恶啉-2-羧酸(MQCA)残留的超高效液相色谱-串联质谱(UPLC-MS/MS)检测方法。采用0.2 mol/L盐酸提取可食性组织中的分析物,经C18固相萃取小柱净化、35 ℃氮气吹干及含0.1%(v/v)甲酸的乙腈溶解后,采用超高效液相色谱分离,串联质谱法确证和定量分析。质谱检测采取正离子多反应监测模式,外标法定量。结果表明: MQCA在2～500 μg/L范围内呈良好的线性关系,各组织中的相关系数(r2)均大于0.990;猪肉、猪肝、猪肾、鱼、对虾和蟹中MQCA的检出限依次为0.90、1.51、0.94、1.04、1.62和1.80 μg/kg,定量限依次为3.00、5.02、3.13、3.46、5.40、6.00 μg/kg。从3～100 μg/kg的添加浓度的检测结果可以看出,MQCA的平均回收率均在73.6%与89.0%之间,日内相对标准偏差(RSD, n=5)在15%以下,日间RSD(n=3)为20%以下。该方法的灵敏度、准确度和精密度均符合兽药残留分析技术的要求,适用于动物组织中MQCA残留的定量分析和确证检测。     

吡啶类含能化合物的合成研究进展

吡啶类化合物在含能材料领域中的研究和应用较为广泛.从分子结构出发,按照硝基吡啶、吡啶类含能离子盐和吡啶类含能配合物分类,综述了多种吡啶硝基衍生物的合成,并简单介绍了一些重要的硝基吡啶类含能化合物的特性及主要应用.     

On Singularity Formation of a Nonlinear Nonlocal System

We investigate the singularity formation of a nonlinear nonlocal system. This nonlocal system is a simplified one-dimensional system of the 3D model that was recently proposed by Hou and Lei (Comm Pure Appl Math 62(4):501–564, 2009) for axisymmetric 3D incompressible Navier–Stokes equations with swirl. The main difference between the 3D model of Hou and Lei and the reformulated 3D Navier–Stokes equations is that the convection term is neglected in the 3D model. In the nonlocal system we consider in this paper, we replace the Riesz operator in the 3D model by the Hilbert transform. One of the main results of this paper is that we prove rigorously the finite time singularity formation of the nonlocal system for a large class of smooth initial data with finite energy. We also prove global regularity for a class of smooth initial data. Numerical results will be presented to demonstrate the asymptotically self-similar blow-up of the solution. The blowup rate of the self-similar singularity of the nonlocal system is similar to that of the 3D model.     

Global existence and blow-up for the degenerate and singular nonlinear parabolic system with a nonlocal source

The existence of a unique classical nonnegative solution is established and the sufficient conditions for the solution that exists globally or blows up in finite time are obtained for the degenerate and singular parabolic system

     

A priori estimates for solutions to nonlinear elliptic equations

Communicated by P. H. Rabinowitz     

5-取代氧化呋咱并[3,4-b]吡啶衍生物的合成与表征

以廉价易得的2,6-二氯吡啶为原料,经过硝化、叠氮化、热解环化步骤得到中间体[1,2,5]噁二唑并[3,4-e]四唑并[1,5-a]吡啶-3-氧化物(4b),再与浓硫酸/硝酸钾、甲醇钠和甲胺水溶液反应分别得到5-取代的氧化呋咱并[3,4-b]吡啶衍生物5~7。 研究了化合物4b结构的稳定性,发现其中的氧化呋咱环在强酸性、强碱性和弱碱性条件下较稳定,而吡啶环与叠氮基形成的四唑环结构则不太稳定。