Computational modelling of multi-material energetic materials and systems

ABSTRACT

In this paper, we present a systematic roadmap for developing a robust and parallel multi-material reactive hydrodynamic solver that integrates historically stable algorithms with new and current modern methods to solve explosive system design problems. The Ghost Fluid Method and Riemann solvers were used to enforce appropriate interface boundary conditions. Improved performance in terms of computational work and convergence properties was achieved by modifying a local node sorting strategy that decouples ghost nodes, allowing us to set material boundary conditions via an explicit procedure, removing the need to solve a coupled system of equations numerically. The locality and explicit nature of the node sorting concept allows for greater levels of parallelism and lower computational cost when populating ghost nodes. Non-linear numerical issues endemic to the use of real Equations of State in hydro-codes were resolved by using more thermodynamically consistent forms allowing us to accurately resolve large density gradients associated with high energy detonation problems at material interfaces. Pre-computed volume tables were implemented adding to the robustness of the solver base.     

Decay of 1.643 h <Superscript>95</Superscript>Ru and its daughter's level structure

The decay of ⁹⁵Ru has been investigated by means of γ-ray spectroscopy. The ⁹⁵Ru nuclei were produced by the reaction ⁹²Mo( α, n) ⁹⁵Ru at a beam energy of 17MeV. High-purity Ge detectors have been used singly and in coincidence to study γ-rays in the decay of ⁹⁵Ru to ⁹⁵Tc. 132 γ-rays are reported, among them, energies and intensities for 127 transitions have been determined. A decay scheme of ⁹⁵Ru with 31 levels is proposed which accommodates 127 of these transitions. Spins and parities for three new levels are proposed from calculated log ft values, measured γ-ray branching ratios, and in-beam experiment results of the daughter nucleus ⁹⁵Tc. Combining with the high-spin states observed by in-beam γ-ray spectroscopy of previous decay works, the structure of the excited states of ⁹⁵Tc is discussed in the framework of the projected shell model.     

Structure of 231Ac: Measurements of level half-lives

There is lack of knowledge of the structure of the ²³¹Ac nucleus located in the upper border of the island of octupole deformation centered around A = 225. We have populated the excited states in ²³¹Ac by beta-decay from the parent ²³¹Ra produced at ISOLDE, CERN. The low-energy structure of ²³¹Ac has been investigated by means of γ, conversion electrons, γ-γ and γ-e^- spectroscopy. We report here in the precise determination in ²³¹Ac of the half-life of the most intensively populated states by the Advanced Time Delayed ββγ(t) technique.     

GSI experiments on synthesis and nuclear structure investigations of the heaviest nuclei

Isotopes of elements up to Z = 113 have been synthesized using medium heavy projectiles and target nuclei around doubly magic ²⁰⁸Pb. Synthesis of still heavier elements in reactions of ⁴⁸Ca projectiles with actinide target nuclei has been reported. To obtain more information about production mechanism of transfermium isotopes nuclear reaction studies including investigations of massive transfer were resumed at SHIP, GSI. Nuclear structure investigations at SHIP have been concentrated so far mainly on systematic investigations of low lying Nilsson levels in odd-mass nuclei. Recently this field has been extended to decay studies of isomeric states in nobelium nuclei at E^* > 1 MeV.     

Characterization of the Landau expansion equation for SrTiO3 under pressure

This work focuses on the characterization of the expansion of Landau's main equation for Pm3?m structures, which are transformed with symmetry subgroups, associated with M+3 and R+4 special points of the Brillouin zone, under hydrostatic pressure. This solution has been adapted to include the general influence of hydrostatic pressure and the evolution of the order parameter. We present a simple scheme in order to search systematically the ground state of all perovskite structures derivable from octahedral rotations under high pressure. We have applied this adaptation to SrTiO₃ perovskite. Results of the characterization of Landau′s equation for the cubic-tetragonal phase transition under pressure are discussed here.     

硅烯中受电场调控的体能隙和朗道能级

近年来, 硅烯(单层硅)由于其独特的结构和电子性质以及在量子霍尔效应等领域的潜在应用而成为理论和实验研究的一个热点. 借助于四带次近邻紧束缚模型, 详细计算和研究了硅烯中受电场调制的体能隙和电子能级. 结果表明: 硅烯原胞中的两个子格处于不同的平面上, 可以通过外电场区分和控制这两个子格, 这将破坏在纯石墨烯中无法被破坏的K-K'对称性, 并消除由这一对称性导致的电子能级的二重简并; 外加电场还会引起硅烯中次近邻格点之间的Rashba自旋轨道耦合, 这一作用会在不同狄拉克点有选择地消除电子能级在部分电场点的简并, 相邻能级从交叉状态变为反交叉状态; 电子能级中除一些孤立的交叉点外, 每个能级都具有确定的自旋取向, 石墨烯中电子能级的四重简并在硅烯中被完全消除, 从而导致填充因子ν=0, ±1, ±2, ±3,…的量子霍尔平台.     

The A = 51 mirror nuclei 51Fe and 51Mn

Eighteen previously unknown γ-ray transitions were identified in the T _z = - 1/2 nucleus ⁵¹Fe following the fusion-evaporation reaction ³²S(²⁸Si,2α1n)⁵¹Fe. The level scheme reaches the fully aligned I ^π = 27/2^- terminating state of the five holes in the f _7/2 shell. The 17/2^- state was found to be isomeric, and the lifetime was measured to be 2.87 ns. The mirror symmetry of ⁵¹Fe and ⁵¹Mn is discussed, and the level scheme of ⁵¹Fe is compared to shell-model calculations. Received: 20 July 2000 / Accepted: 1 August 2000     

Landau damping of ion-acoustic waves with simultaneous effects of non-extensivity and non-thermality in the presence of hybrid Cairns-Tsallis distributed electrons

The dispersion properties and Landau damping rate of ion-acoustic waves (IAWs) with the hybrid Cairns-Tsallis distributed (CTD) electrons and Maxwellian ions are investigated using the plasma kinetic model based on Vlasov-Poisson's equations. For both super-extensive (q < 1) and sub-extensive (q > 1) plasmas, the dielectric response function, real frequency, and Landau damping rate of IAWs are derived. By taking the effect of θ_{i, e} (ion-to-electron temperature ratio) into account, it is found that with the increase of ion temperature, the real frequency and wave dispersion effects increase as well (for both super-extensive and sub-extensive cases). Exploring the properties of the Landau damping rate of IAWs with the simultaneous presence of non-thermal parameter α and non-extensive parameter q, a comparison of numerical and analytical results is presented. It is found that in different ranges of θ_{e, i} (electron-to-ion temperature ratio), on decreasing the values of the non-extensive parameter and increasing values of the non-thermal parameter, the weak damping rate is observed (vice versa) in super-extensive or super-thermal plasma, although the trend of the damping rate in sub-thermal plasma is similar (as in the case of super-thermal plasma) but is less weak. It is further revealed that the damping rate of IAWs in thermal plasmas (Maxwellian) is stronger than the damping rate of IAWs in the case of non-thermal plasmas (CTD). The current study is applicable to provide deep insight and further allow the exploration of electrostatic plasma modes in different space and laboratory plasma environments where the hybrid CTD plasma exists.     

基于窄带多区域水平集方法的遥感图像分割

由于遥感图像存在边缘混叠等问题,经典的C-V模型会产生大量的冗余轮廓,而且无法分割多个同质区域的目标.为此,提出了基于C-V模型的窄带多区域水平集图像分割方法,采用N-1个水平集函数将图像分割成N(N＞1)个区域,每个水平集函数表达一个区域.该方法一方面通过建立独立多区域水平集模型可以消除多余的轮廓,避免分割区域的重叠...     

First observation of trapped high-field seeking ultracold neutron spin states

Ultracold neutrons were stored in a volume, using a magnetic dipole field shutter. Radial confinement was provided by material walls. Low-field seeking neutrons were axially confined above the magnetic field. High-field seeking neutrons are trapped inside the magnetic field. They can systematically shift the measured neutron lifetime to lower values in experiments with magnetic confinement.