Characteristics of the initiation of chain and thermal explosions of energetic materials by pulsed laser radiation

A comparative experimental and theoretical study of the initiation of silver azide (SA) single crystals and pressed pentaerythritol tetranitrate (PETN)–metal nanoparticles by a neodymium laser pulse is performed. The main differences in the explosive decomposition of the samples are associated with the absence of the induction period and the presence of subthreshold effects in the initiation of PETN-based composites. By contrast, the initiation of SA single crystals always features an induction period, but no subthreshold effects. It is shown that the observed differences in the explosive decomposition are due to the fact that SA single crystals decompose by the chain explosion mechanism, whereas pressed PETN–metal nanoparticles samples, by the thermal explosion mechanism in the micro-hotspot mode. The kinetic parameters of the initiation of the decomposition reaction calculated within the framework of the existing model are consistent with the available experimental data. An experimental criterion for distinguishing between the chain and thermal (in micro-hotspot) mechanisms of the initiation of an explosion under the action of a laser radiation pulse is formulated, according to which the absence of the induction period and a pronounced manifestation of subthreshold effects are indicative of a thermal explosion, whereas the presence of the induction period and the absence of subthreshold effects are characteristic of a chain explosion.     

On the spectral theory of the Bessel operator on a finite interval and the half-line

We study the minimal and maximal operators generated by the Bessel differential expression on a finite interval and the half-line. We describe the domains of the Friedrichs and Krein extensions of the minimal operator and all nonnegative self-adjoint extensions of the minimal operator.     

Characterization of bupivacaine-loaded formulations based on liquid crystalline phases and microemulsions: the effect of lipid composition

This report details the structural characterization and the in vitro drug-release properties of different local anesthetic bupivacaine (BUP)-loaded inverted-type liquid crystalline phases and microemulsions. The effects of variations in the lipid composition and/or BUP concentration on the self-assembled nanostructures were investigated in the presence of the commercial distilled glycerol monooleate Myverol 18-99K (GMO) and medium-chain triglycerides (MCT). Synchrotron small-angle X-ray scattering (SAXS) and rotating dialysis cell model were used to characterize the BUP formulations and to investigate the in vitro BUP release profiles, respectively. The evaluation of SAXS data for the BUP-loaded GMO/MCT formulations indicates the structural transition of inverted-type bicontinuous cubic phase of the symmetry Pn3m → inverted-type hexagonal (H(2)) phase → inverted-type microemulsion (L(2)) with increasing MCT content (0-40 wt %). In the absence of MCT, the solubilization of BUP induces the transition of Pn3m → H(2) at pH 7.4; whereas a transition of Pn3m → (Pn3m + H(2)) is detected as the hydration is achieved at pH 6.0. To mimic the drug release and transport from in situ formed self-assembled systems after subcutaneous administration, the release experiments were performed by injecting low viscous stimulus-responsive precursors to a buffer in the dialysis cell leaving the surface area between the self-assembled system and the release medium variable. Our results suggest that the pH-dependent variations in the lipidic partition coefficient, K(l/w), between the liquid crystalline nanostructures and the surrounding buffer solution are significantly affecting BUP release rates. Thus, a first step toward understanding of the drug-release mechanism of this drug-delivery class has been undertaken tackling the influence of drug ionization as well as the type of the self-assembled nanostructure and its release kinetics under pharmaceutically relevant conditions.     

Grafting copolymerization of vinyl monomers on polyimide macroinitiators by the method of atom transfer radical polymerization

Graft copolymers with the main polyimide chain and side chains of poly(n-butyl acrylate), poly(tert-butyl acrylate), poly(methyl methacrylate), poly(tert-butyl methacrylate), polystyrene, and polystyrene-block-poly(methyl methacrylate) were synthesized by atom transfer radical polymerization on the multicenter polyimide macroinitiators in the presence of the halide complexes of univalent copper with nitrogen-containing ligands. Polymerization of metha-crylates is most efficiently developed on the polyimide macroinitiators. The obtained graft copolymers initiate the secondary polymerization (“post-polymerization”) of methyl methacrylate. The conditions of detachment of side chains of graft polymethacrylates that do not involve the ester groups of their monomeric units were found. The molecular mass characteristics of the graft copolymers and isolated polymers, being the detached side chains of the copolymers, were determined. The detached side chains of different chemical structures have low values of the polydispersity index. The procedure developed was used for the preparation of new graft polyimides with side chains of poly-4-nitro-4′-[N-methylacryloyloxyethyl-N′-ethyl]amino-azobenzene that cause the nonlinear optical properties and with the side chains of poly(N,N-dimethylaminoethyl methacrylate) that cause the thermosensitive properties of the copolymers.     

Simulations of liquid ammonia based on the combined quantum mechanical/molecular mechanical (QM/MM) approach

Two combined quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations, namely, HF/MM and B3LYP/MM, have been performed to investigate the local structure and dynamics of liquid ammonia. The most interesting region, a sphere containing a central reference molecule and all its nearest surrounding molecules (first coordination shell), was treated by the Hartree-Fock (HF) and hybrid density functional B3LYP methods, whereas the rest of the system was described by the classical pair potentials. On the basis of both HF and B3LYP methods, it is observed that the hydrogen bonding in this peculiar liquid is weak. The structure and dynamics of this liquid are suggested to be determined by the steric packing effects, rather than by the directional hydrogen bonding interactions. Compared to previous empirical as well as Car-Parrinello (CP) molecular dynamics studies, our QM/MM simulations provide detailed information that is in better agreement with experimental data.     

Synthesis and molecular structures of the Co3(μ-OOCPh)4(μ,η2-OOCPh)2[OC(Ph)OHNEt3]2 and Co(Hdmpz)2(OOCPh)2 complexes (Hdmpz = 3,5-dimethylpyrazole)

The product of the thermal reaction between cobalt acetate hydrate and benzoic acid reacts with a triethylamine excess to form the trinuclear complex Co₃(μ-OOCPh)₄(μ,η²-OOCPh)₂[OC(Ph)OHNEt₃]₂, and its reaction with 3,5-dimethylpyrazole yields the mononuclear complex Co(Hdmpz)₂(OOCPh)₂. The compound structures are discussed on the basis of X-ray crystallographic data.     

Reactions of aqueous copper acetate with triethylamine and 3,5-dimethylpyrazole

The dissolution of aqueous copper acetate in tetrahydrofuran gives the Cu₂(μ-OOCMe)₄(thf)₂ complex (1), and its reaction with triethylamine in the presence of acetic acid yields “[Cu₂(μ-OOCMe)₄[μ-OOCMe(HNEt₃)]” _n polymer (2). Complexes 1 and 2 react with 3,5-dimethylpyrazole to form Cu(Hdmpz)₂(OOCMe)₂ (3) and Cu₂(μ-OOCMe)₄(Hdmpz)₂ (4), respectively. The structures of complexes 1–4 and that of solvate 4 × 0.5C₆H₆ (5) are determined by X-ray diffraction.     

Differential geometry of grassmannians and the Plücker map

Using the Plücker map between grassmannians, we study basic aspects of classic grassmannian geometries. For ‘hyperbolic’ grassmannian geometries, we prove some facts (for instance, that the Plücker map is a minimal isometric embedding) that were previously known in the ‘elliptic’ case.     

SiC JBS二极管和SiC MOSFET的空间辐照效应及机理

基于第六代650 V碳化硅结型肖特基二极管(SiC JBS Diode)和第三代900 V碳化硅场效应晶体管(SiC MOSFET),开展SiC功率器件的单粒子效应、总剂量效应和位移损伤效应研究。20～80 MeV质子单粒子效应实验中,SiC功率器件发生单粒子烧毁(SEB)时伴随着波浪形脉冲电流的产生,辐照后SEB器件的击穿特性完全丧失。SiC功率器件发生SEB时的累积质子注量随偏置电压的增大而减小。利用计算机辅助设计工具(TCAD)开展SiC MOSFET的单粒子效应仿真,结果表明,重离子从源极入射器件时,具有更短的SEB发生时间和更低的SEB阈值电压。栅-源拐角和衬底-外延层交界处为SiC MOSFET的SEB敏感区域,强电场强度和高电流密度的同时存在导致敏感区域产生过高的晶格温度。SiC MOSFET在栅压偏置(U_GS=3 V,U_DS=0 V)下开展钴源总剂量效应实验,相比于漏压偏置(U_GS=0 V,U_DS=300 V)和零压偏置(U_GS=U_DS=0...     

舰载导弹电源线尖峰信号敏感度指标要求与考核

舰载导弹在值班状态时被认为是一种舰上设备，在飞行状态时被认为是一种飞行器。GJB151B-2013中明确了舰载平台设备需进行CS106项目检测，而导弹由于并非直接与舰上电网连接，如若仍按照GJB151B-2013中规定的尖峰信号指标进行考核，明显存在过试验的情况。针对舰载导弹在电磁兼容CS106指标的裁剪需求，对其考核要求进行了充分的分析和研究，并给出了试验的裁剪建议。