以RDX为基的含铝炸药中铝粉粒度和氧化剂形态对加速金属能力的影响

利用激光速度干涉仪研究了含微米铝粉和纳米铝粉复合炸药加速金属平板的能力,结果表明纳米铝粉的引入能够获得更大的金属平板自由面速度,其反应时间比微米复合含铝炸药缩短35.1%。研究了氧化剂的形态对含铝炸药性能的影响,用物理化学手段获得的RDX/AP复合粒子复合粒子制作的含铝炸药加速金属平板的能力优于机械混合RDX/AP的含铝炸药,前者的反应时间也比后者短。此外,还研究了以富氧炸药取代RDX获得的含铝炸药的性能,结果表明其加速金属平板的速度比RDX/Al复合炸药提高10%。     

分散剂对YAG粉末形貌和性能的影响

以硝酸铝［Al(NO3)39H2O］和硝酸钇［Y(NO3)36H2O］为原料,碳酸氢铵［NH4HCO3］为沉淀剂,PEG400,PEG800和PEG1000等为分散剂,采用正向共沉淀法合成了钇铝石榴石（YAG）前驱体粉末。并用X射线衍射仪（XRD）、扫描电子显微镜（SEM）、粒度测试仪等分析了粉末的形貌和性能。结果表明,分散剂的加入,减少了粉末的团聚现象,而且由PEG400,PEG800分散剂制备的先驱体粉末经1200 ℃煅烧60 min后均能形成纯度较高的YAG相,但PEG1000样品粒度更细,比表面积为1748.78 m2/kg,中位径为1.42 m,而前者所得粉末的比表面积分别为29.39和128.60 m2/kg,中位径分别为196.14和20.55 m。     

Theoretical studies on the structure,sensitivity, density,thermodynamic properties and detonation performance of dinitrobitriazoles

Azodinitro- and dinitroethylene-bridged bitriazoles are of interest in the contest of high explosives, and were found to have true local energy minima at the B3LYP/aug-cc-pVDZ level of theory. The optimised structures, vibrational frequencies and thermodynamic quantities for bitriazoles were obtained in the ground state. Kamlet–Jacobs equations were used to evaluate the performance of bitriazoles based on the predicted density and the calculated heat of explosion. Detonation properties (D = 8.12 to 9.23 km s^?1 and P = 28.0 to 39.83 GPa) of bitriazoles were found to be promising compared with those of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX, D = 8.75 km s^?1 and P = 34.7 GPa) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX, D = 8.96 km s^?1 and P = 35.96 GPa). The fusion of azoles particularly appears to be a promising area for investigation, since it may lead to the desirable consequences of higher heat of explosion, higher density and thus improved detonation performance.     

The Lévy Swap Market Model

Models driven by Lévy processes are attractive since they allow for better statistical fitting than classical diffusion models. The dynamics of the forward swap rate process is derived in a semimartingale setting and a Lévy swap market model is introduced. In order to guarantee positive rates, the swap rates are modelled as ordinary exponentials. The model starts with the most distant rate, which is driven by a non‐homogeneous Lévy process. Via backward induction the remaining swap rates are constructed such that they become martingales under the corresponding forward swap measures. Finally it is shown how swaptions can be priced using bilateral Laplace transforms.     

Forward Variance Dynamics: Bergomi’s Model Revisited

Abstract

In this article, we propose an arbitrage-free modelling framework for the joint dynamics of forward variance along with the underlying index, which can be seen as a combination of the two approaches proposed by Bergomi. The difference between our modelling framework and the Bergomi (2008. Smile dynamics III. Risk, October, 90–96) models is mainly the ability to compute the prices of VIX futures and options by using semi-analytic formulas. Also, we can express the sensitivities of the prices of VIX futures and options with respect to the model parameters, which enables us to propose an efficient and easy calibration to the VIX futures and options. The calibrated model allows to Delta-hedge VIX options by trading in VIX futures, the corresponding hedge ratios can be computed analytically.     

An MPI parallel level-set algorithm for propagating front curvature dependent detonation shock fronts in complex geometries

We present a parallel, two-dimensional, grid-based algorithm for solving a level-set function PDE that arises in Detonation Shock Dynamics (DSD). In the DSD limit, the detonation shock propagates at a speed that is a function of the curvature of the shock surface, subject to a set of boundary conditions applied along the boundaries of the detonating explosive. Our method solves for the full level-set function field, φ(x, y, t), that locates the detonation shock with a modified level-set function PDE that continuously renormalises the level-set function to a distance function based off of the locus of the shock surface, φ(x, y, t)=0. The boundary conditions are applied with ghost nodes that are sorted according to their connectivity to the interior explosive nodes. This allows the boundary conditions to be applied via a local, direct evaluation procedure. We give an extension of this boundary condition application method to three dimensions. Our parallel algorithm is based on a domain-decomposition model which uses the Message-Passing Interface (MPI) paradigm. The computational order of the full level-set algorithm, which is O(N ⁴), where N is the number of grid points along a coordinate line, makes an MPI-based algorithm an attractive alternative. This parallel model partitions the overall explosive domain into smaller sub-domains which in turn get mapped onto processors that are topologically arranged into a two-dimensional rectangular grid. A comparison of our numerical solution with an exact solution to the problem of a detonation rate stick shows that our numerical solution converges at better than first-order accuracy as measured by an L1-norm. This represents an improvement over the convergence properties of narrow-band level-set function solvers, whose convergence is limited to a floor set by the width of the narrow band. The efficiency of the narrow-band method is recovered by using our parallel model.     

Statistical analysis of cellular detonation dynamics from numerical simulations: one-step chemistry

In this paper, two methods are developed for statistically analysing the nonlinear cellular dynamics from numerical simulations of gaseous detonations, one use of which is the systematic determination of detonation cell sizes from such simulations. Both these methods rely on signed vorticity records in which the individual families of transverse waves are captured independently. The first method involves an automated extraction of the main triple-point tracks from the vorticity records, allowing statistical analysis of the spacings between neighbouring tracks. The second method uses the autocorrelation function to spectrally analyse the vorticity records. These methods are then employed for a preliminary analysis of the cellular dynamics of the standard, idealized one-step chemistry model. Evidence is found for ‘cell size doubling’ bifurcations in the one-step model as the cellular dynamics become more irregular (e.g. as the activation is increased). It is also shown that the statistical models converge slowly due to systematic ‘shot-to-shot’ variation in the cellular dynamics for fixed parameters with different initial perturbations. Instead, it appears that a range of equally probable cell sizes can be obtained for given parameters.     

Structure and detonation performance of a novel HMX/LLM‐105 cocrystal explosive

Intermolecular interactions and properties of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐ tetrazocine (HMX) / 2,6‐diamino‐3,5‐dinitropyrazine‐1‐oxide (LLM‐105) cocrystal were studied by using the dispersion‐corrected density functionals (ωB97XD, B97D) and meta‐hybrid functional (M062x) methods. Binding energies, heats of formation, thermodynamic properties, atoms in molecules, and natural bond orbital analysis were performed to investigate HMX/LLM‐105 complexes. Results show that the main intermolecular interactions between HMX and LLM‐105 are CH…O, NH…O, N…O, and O…O interactions. In addition, Monte Carlo simulation was employed to predict the crystal structure of HMX/LLM‐105 cocrystal. The HMX/LLM‐105 cocrystal is most likely to crystallize in C2/c space group, and its corresponding cell parameters are Z = 8, a = 41.63 Å, b = 6.77 Å, c = 45.63 Å, ß = 164.55°, and ρ = 1.99 g/cm³. Detonation velocity and pressure of HMX/LLM‐105 cocrystal are 8.95 km/s, 37.69GPa, a little lower than those of HMX (9.10 km/s, 37.76GPa). However, according to the net charges of nitro group, HMX/LLM‐105 cocrystal exhibits less sensitive than HMX. Finally, bond dissociation energy calculation shows that HMX/LLM‐105 complexes are thermally stable. Considering thermal stability, sensitivity, and detonation performance, HMX/LLM‐105 cocrystal meets the requirements of insensitive high energy density materials. Copyright © 2013 John Wiley & Sons, Ltd.