Synthesis of Thermally Stable Energetic 1,2,3‐Triazole Derivatives

Various thermally stable energetic polynitro‐aryl‐1,2,3‐triazoles have been synthesized through Cu‐catalyzed [3+2] cycloaddition reactions between their corresponding azides and alkynes, followed by nitration. These compounds were characterized by analytical and spectroscopic methods and the solid‐state structures of most of these compounds have been determined by using X‐ray diffraction techniques. Most of the polynitro‐bearing triazole derivatives decomposed within the range 142–319 °C and their heats of formation and crystal densities were determined from computational studies. By using the Kamlet–Jacobs empirical relation, their detonation velocities and pressures were calculated from their heats of formation and crystal densities. Most of these newly synthesized compounds exhibited high positive heats of formation, good thermal stabilities, reasonable densities, and acceptable detonation properties that were comparable to those of TNT.     

Robust numerical analysis of the dynamic bubble formation process in a viscous liquid

The dynamics of bubble formation from a submerged nozzle in a highly viscous liquid with relatively fast inflow gas velocity is studied numerically. The numerical simulations are carried out using a sharp interface coupled level set/volume-of-fluid (CLSVOF) method and the governing equations are solved through a hydrodynamic scheme with formal second-order accuracy. Numerical results agree well with experimental results and it is shown that the sharp interface CLSVOF method enables one to reproduce the bubble formation process for a wide range of inflow gas velocities. From numerical results, one can improve their understanding of the mechanisms regarding the dynamics of bubble formation. For example, it is found that for some sets of parameters that the bubble formation process reaches steady state after several bubbles are released from the nozzle. At steady state, bubbles uniformly rise freely in the viscous liquid. It is observed that the fluid flow around a formed bubble has a significant role in determining the overall dynamic process of bubble formation; e.g. the effect of the fluid flow from the preceding bubble can be seen on newly formed bubbles.     

Experimental Study of the Rate of Unsteady Fluid Flow from a Prefilled Vessel

The variation of the flow-rate of a fluid flowing out of a prefilled cylindrical vessel through sinkholes with a diameter less than 0.1 of the vessel diameter has been studied experimentally. The study was carried out in both the presence and the absence of a vortex funnel around the sinkhole. In these experiments the vessel was filled in such a way that a funnel was formed only when a disk immersed in the fluid was rotated before the sinkhole was opened. The time dependence of the flow-rate is found for various initial heights and rates of artificial swirl. Four different outflow stages were detected. It is shown that for certain flow parameters there is a time interval on which the fluid flow-rate is independent of the column height. A critical rotation velocity W _0* below which (W ₀ < W _0*) an intense funnel is not formed is found. A limiting curve approached by all the flow-rate curves in the final stage of outflow is obtained.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 113–121.Original Russian Text Copyright © 2005 by Shtarev.     

The ornithine effect in peptide cation dissociation

Facile cleavage C‐terminal to ornithine residues in gas phase peptides has been observed and termed the ornithine effect. Peptides containing internal or C‐terminal ornithine residues, which are formed from deguanidination of arginine in solution, were fragmented to produce either a y‐ion or water loss, respectively, and the complementary b‐ion. The fragmentation patterns of several peptides containing arginine were compared to those of the ornithine analogues. Conversion of arginine to ornithine results in a decrease of the gas phase proton affinity of the residue, thereby increasing the mobility of the ionizing proton. This alteration allows the nucleophilic amine to facilitate a neighboring group reaction to induce a cleavage of the adjacent amide bond. The selective cleavage at the ornithine residue is proposed to result from the highly favorable generation of a six‐membered lactam ring. The ornithine effect was compared with the well‐known proline and aspartic acid effects in peptide fragmentation using angiotensin II, DRVYIHPF and the ornithine analogue, DOVYIHPF. Under conditions favorable to either the aspartic acid (i.e. singly protonated peptide) or proline effect (i.e. doubly protonated peptide), the ornithine effect was consistently observed to be the more favorable fragmentation pathway. The highly selective nature of the ornithine effect opens up the possibility for conversion of arginine to ornithine residues to induce selective cleavages in polypeptide ions. Such an approach may complement strategies that seek to generate non‐selective cleavages of the related peptides. Copyright © 2013 John Wiley & Sons, Ltd.     

Heteroclinic contours and self-replicated solitary waves in a reaction–diffusion lattice with complex threshold excitation

The space–time dynamics of the network system modeling collective behavior of electrically coupled nonlinear cells is investigated. The dynamics of a local cell is described by the FitzHugh–Nagumo system with complex threshold excitation. Heteroclinic orbits defining traveling wave front solutions are investigated in a moving frame system. A heteroclinic contour formed by separatrix manifolds of two saddle-foci is found in the phase space. The existence of such structure indicates the appearance of complex wave patterns in the network. Such solutions have been confirmed and analyzed numerically. Complex homoclinic orbits found in the neighborhood of the heteroclinic contour define the propagation of composite pulse excitations that can be self-replicated in collisions leading to the appearance of complex wave patterns.     

Quantum Correlations in a Two-Qubit Heisenberg XX Model under Intrinsic Decoherence

Taking into account the intrinsic decoherence, we have investigated quantum correlations in a two-qubit Heisenberg XX model when a nonuniform magnetic field is included. We compare entanglement measured by entanglement of formation, quantum discord and measurement-induced measurement (MID) and illustrate their different characteristics. Quantum discord and MID show the same features and always exist even though there is no entanglement in the long time limit. In the time evolution, quantum discord could be generated or enhanced to the stable value, while MID just decreases to the stable value.     

CdS纳米棒的水热法制备及形成机理研究

采用水热法以Na2S· 9H2O为硫源,Cd3O12S3·8H2O为镉源,PVP为表面活性剂,成功制备了CdS纳米棒.并利用X射线衍射(XRD)、透射电子显微镜(TEM)和相应选区电子衍射(SAED)、高分辨透射电子显微镜(HRTEM)、X射线能量色散分析谱仪(XEDS)和紫外可见(UV-vis)分光光度计等测试手段对样品的晶体结构、形貌、微观结构和光学特性等特征进行了表征分析,实验结果表明本方法所制备的CdS纳米棒为纤锌矿结构,沿[001]方向择优生长,平均直径大约为50 nm,棒宽均匀、分散性好,带隙为2.43 eV.同时也对CdS纳米棒的形成机理进行了初步探讨,提出了CdS纳米棒的生长模型,其形貌从三角形到阶梯形棒晶,最后再到完整的棒状晶体的一个定向团聚的自组装过程.     

ZnSb2O4纳米正三角形的合成与生长机理讨论

以混合的ZnO粉和金属Sb作为前驱物,通过化学气相沉积方法在Si衬底上合成了ZnSb2O4纳米正三角形.利用场发射扫描电子显微镜、透射电子显微镜以及附带的能谱仪对它们的结构和成分进行了表征.并对ZnSb2O4纳米正三角形的生长机理进行了讨论.     

DFT Study on Molecule C20H10:Five Carbon-carbon Single Bonds Linking Two Pentaprismane Cages

1 INTRODUCTION In recent years, a great number of achievements have been achieved in the field of molecules with cage-like structures, such as fullerenes and poly- hedral hydrocarbons. Each of these molecules has only one cage, such as C60 and dodecahedrane. As is well known, every carbon atom can form four single bonds with other atoms. Since each carbon atom at the cage surface of the carbo-polyhedral molecule only forms three bonds with other carbon atoms, it may form the fourth singl…     

Gas-phase thermochemical properties of some tri-substituted phenols: A density functional theory study

The study of the energetics of phenolic compounds has a considerable practical interest since this family of compounds includes numerous synthetic and naturally occurring antioxidants. In this work, density functional theory (DFT) has been used to investigate gas-phase thermochemical properties of the following tri-substituted phenols: 2,4,6-trimethylphenol, 2,6-dimethyl-4-tert-butylphenol, 2,6-dimethyl-4-methoxyphenol, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-methoxyphenol, 2,4,6-trimethoxyphenol, 2,6-dimethoxy-4-methylphenol and 2,6-dimethoxy-4-tert-butylphenol. Molecular structures were computed with the B3LYP and the ωB97X-D functionals and the 6-31G(d) basis set. More accurate energies were obtained from single-point energy calculations with both functionals and the 6-311++G(2df,2pd) basis set. Standard enthalpies of formation of the phenolic molecules and phenoxyl radicals were derived using an appropriate homodesmotic reaction. The OH homolytic bond dissociation enthalpies, gas-phase acidities and adiabatic ionization enthalpies were also calculated. The general good agreement found between the calculated and the few existent experimental gas-phase thermochemical parameters gives confidence to the estimates concerning the phenolic compounds which were not yet experimentally studied.