冷速对液态金属Mg凝固过程中微观结构演变的影响

采用分子动力学方法对不同冷速下液态金属镁(Mg)快速凝固过程中的微观结构演变进行了模拟研究.并采用能量-温度(E-T)曲线、双体分布函数、Honeycutt-Andersen键型指数法、原子团簇类型指数法(CTIM-3)以及三维可视化等方法系统地考察了凝固过程中微观结构演变与相转变过程.结果发现:在以冷速为1×10~(11)K/s的凝固过程中,亚稳态bcc相优先形成,随后大量解体,其变化规律符合Ostwald规则,系统最终形成以hcp结构为主体与fcc结构共存,中间还夹杂部分bcc结构的致密晶体结构.在1×10~(12)K/s冷速下,结晶过程呈现迟缓现象,形成bcc结构的初始温度降低,系统形成以hcp居多、与bcc和fcc三相共存的结构,且因相互竞争、相互制约而导致不易形成粗大的晶粒结构.而在1×10~(13)K/s冷速下,系统则形成以1551,1541,1431键型为主的多种非晶态基本原子团组成的非晶态结构.此外,在冷速1×10~(12)与1×10~(13)K/s之间的确存在一个形成非晶态结构的临界冷速.     

Oriented Shadowing Property and $$\Omega $$-Stability for Vector Fields

We call that a vector field has the oriented shadowing property if for any \(\varepsilon >0\) there is \(d>0\) such that each \(d\)-pseudo orbit is \(\varepsilon \)-oriented shadowed by some real orbit. In this paper, we show that the \(C^1\)-interior of the set of vector fields with the oriented shadowing property is contained in the set of vector fields with the \(\Omega \)-stability.     

Two quantum dialogue protocols without information leakage

By swapping the entanglement of Bell states, we propose two quantum dialogue protocols, which have two different characters, one with the “two-step” character and the other with the “ping-pong” character. The common merits of two dialogue protocols are that the information leakage does not exist.     

An equation of state for the detonation product of copper oxide/aluminum nanothermite composites

An equation of state (EOS) for the detonation product of the copper oxide/aluminum (CuO/Al) nanothermite composites is developed based on the Chapman–Jouguet (CJ) theory and the nanothermite detonation experiment. The EOS is implemented into a coupled computational fluid dynamics and computational solid dynamics code through the material point method for the model-based simulations of the detonation response of the CuO/Al nanothermite material placed in a small well. The simulations demonstrate the validity of the formulated EOS to catch the essential feature of the detonation response of the CuO/Al nanothermite. The EOS parameters are determined by comparing simulated and experimentally measured pressure–time histories.     

Interaction of in-band and in-gap lattice soliton trains in optically induced two-dimensional photonic lattices

We demonstrate the coherent interactions of lattice soliton trains, including in-band solitons (IBSs) and gap soliton trains (GSTs), in optically induced two-dimensional photonic lattices with self-defocusing nonlinearity. It is revealed that the $\pi$-staggered phase structures of the lattice soliton trains will lead to anomalous interactions. Solely by changing their initial separations, the transition between attractive and repulsive interaction forces or reversion of the energy transfer can be obtained. The `negative refraction' effect of the soliton trains on the interaction is also discussed. Moreover, two interacting IBSs can merge into one GST when attraction or energy transfer happens.     

Single‐Molecule Measurement of Adsorption Free Energy at the Solid–Liquid Interface

Adsorption plays a critical role in surface and interface processes. Fractional surface coverage and adsorption free energy are two essential parameters of molecular adsorption. However, although adsorption at the solid–gas interface has been well‐studied, and some adsorption models were proposed more than a century ago, challenges remain for the experimental investigation of molecular adsorption at the solid–liquid interface. Herein, we report the statistical and quantitative single‐molecule measurement of adsorption at the solid–liquid interface by using the single‐molecule break junction technique. The fractional surface coverage was extracted from the analysis of junction formation probability so that the adsorption free energy could be calculated by referring to the Langmuir isotherm. In the case of three prototypical molecules with terminal methylthio, pyridyl, and amino groups, the adsorption free energies were found to be 32.5, 33.9, and 28.3 kJ mol^?1, respectively, which are consistent with DFT calculations.     

Rhodium(I)/Zn(OTf)2‐Catalyzed Asymmetric Ring Opening/Cyclopropanation of Oxabenzonorbornadienes with Phosphorus Ylides

The strong binding ability of P‐ylides with transition metals limits the utilization of stabilized P‐ylide as nucleophiles in asymmetric organometallic catalysis. Herein we describe the first rhodium‐catalyzed asymmetric ring‐opening reaction of P‐ylides utilizing oxabicyclic alkenes as the electrophilic partner. Various P‐ylides including ester‐, ketone‐ and amide‐style P‐ylides are all applicable. This asymmetric reaction occurs through the cleavage of two bridgehead C?O bonds and the formation of two C?C bonds, and oxabenzonorbornadienes are used as 1,4‐biselectrophiles, thus providing access to benzonorcaradienes in good yields with high enantioselectivity and perfect diastereoselectivity. The present protocol also constitutes the first highly enantioselective direct catalytic asymmetric cyclopropanation of stabilized P‐ylide nucleophiles.     

Concise Synthesis of Open‐Cage Fullerenes for Oxygen Delivery

Open‐cage fullerenes with a 19‐membered orifice were prepared in three steps from C₆₀. The key step for cage‐opening is aniline mediated ring expansion of a fullerene‐mixed peroxide with a ketolactone moiety on the orifice. Release of ring strain on the spherical fullerene cage served as the main driving force for the efficient cage‐opening sequence. Encapsulation of oxygen could be achieved at room temperature under moderate pressure (50 atm) and the encapsulated oxygen could be released slowly under ambient conditions. The activation energy of the oxygen‐releasing process is 18.8 kcal mol^?1 and the half‐life at 37 °C was 73 min, which makes this open‐cage fullerene derivative a potential oxygen‐delivery material.     

Computational insight into excited states of the ring-opening radicals from the pyrolysis of furan biofuels

The low-lying valence excited states and Rydberg states of the radical species from the ring-opening reactions in pyrolysis of furan biofuels have been determined by extensive density functional theory and sophisticated wave function theory calculations. The radicals 1-C₄H₅O-2, 2-furylCH₂, and 4-C₆H₇O with the delocalized π-type single electron are predicted to be most stable among the reactive species here for furan, 2-methyfuran, and 2,5-dimethylfuran, respectively. Predicted vertical transition energies by TD-CAM-B3LYP show good agreement with those by CASPT2. Some among the electronic excitations to low-lying states can take place in the visible light region, and they may be involved in the combustion process. Further surface hopping dynamics simulations on the excited states of the most stable ring-opening radical 1-C₄H₅O-2 of furan as an example reveal that 89.9% sampling trajectories at the initial excited state of 2²A”(π¹π*²) decay to the 1²A’(n¹π*²) state within an average of 384 fs, and then 81.2% trajectories at the 1²A’ state go to the ground state within an average of 114 fs. At the end of the simulation for 1000 fs, 18.8% trajectories still stay on the excited states of 2²A” and 1²A’, suggesting that the reactive radicals in the ground state are mainly responsible for the combustion chemistry of furan biofuels. © 2018 Wiley Periodicals, Inc.