Design of Energetic Materials Based on Asymmetric Oxadiazole

A new family of asymmetric oxadiazole based energetic compounds were designed. Their electronic structures, heats of formation, detonation properties and stabilities were investigated by density functional theory. The results show that all the designed compounds have high positive heats of formation ranging from 115.4 to 2122.2 kJ mol⁻¹. −N− bridge/−N₃ groups played an important role in improving heats of formation while −O− bridge/−NF₂ group made more contributions to the densities of the designed compounds. Detonation properties show that some compounds have equal or higher detonation velocities than RDX, while some other have higher detonation pressures than RDX. All the designed compounds have better impact sensitivities than those of RDX and HMX and meet the criterion of thermal stability. Finally, some of the compounds were screened as the candidates of high energy density compounds with superior detonation properties and stabilities to that of HMX and their electronic properties were investigated.     

Theoretical insights on a series of difluoramino group–based energetic molecules

A series of difluoramino group–based energetic molecules was designed and the relative properties were investigated by density functional theory. The results show that all the designed molecules have high positive heat of formation which ranges from 479.48 to 724.02 kJ/mol, detonation velocity ranges from 8.01 to 11.26 km/s, detonation pressure ranges from 28.03 to 63.46 GPa, and impact sensitivity ranges from 18.2 to 54.5 cm. Then, compounds D2, D3, D5, E4, E5, E6, and F2 were selected as the potential high energy density materials based on detonation properties and sensitivities. Natural bond orbital charges, electronic density, frontier molecular orbital, electrostatic potential on the surface, and thermal dynamic parameters of the screened molecules (compounds D2, D3, D5, E4, E5, E6, and F2) were also predicted at B3LYP/6‐31G(d,p) level to give a better understanding on the chemical and physical properties of them.     

Analytical investigation on unstable vibrations of single-mesh gear systems with velocity-modulated time-varying stiffness

Time-varying mesh stiffness parametrically excites gear systems and causes severe vibrations and instabilities. Taking speed fluctuations into account, the time-varying mesh stiffness is frequency modulated, and more complex instabilities might arise. Considering two different speed fluctuation models, parametric instability associated with velocity-modulated time-varying stiffness is analytically investigated using a typical single-mesh gear system model. Closed-form approximations are obtained by perturbation analysis, and verified by numerical analysis. The effects of the amplitude of the mesh stiffness variation, the characteristics of speed fluctuations and damping on parametric instability are systematically examined.     

Consecutive metal oxides with self-supported nanoarchitecture achieves highly stable and enhanced photoelectrocatalytic oxidation for water purification

Journal of Solid State Electrochemistry - Owing to its low cost and plentiful different semiconductor configurations resources, photoelectrocatalysis (PEC) has come into the spotlight in...     

两两NQD序列部分和的强大数定律

By using the moment inequality, maximal inequality and the truncated method of random variables, we establish the strong law of large numbers of partial sums for pairwise NQD sequences, which extends the corresponding result of pairwise NQD random variables.     

Molecular Engineering of a Metal-Organic Polymer for Enhanced Electrochemical Nitrate-to-Ammonia Conversion and Zinc Nitrate Batteries

Metal–organic framework-based materials are promising single-site catalysts for electrocatalytic nitrate (NO₃⁻) reduction to value-added ammonia (NH₃) on account of well-defined structures and functional tunability but still lack a molecular-level understanding for designing the high-efficient catalysts. Here, we proposed a molecular engineering strategy to enhance electrochemical NO₃⁻-to-NH₃ conversion by introducing the carbonyl groups into 1,2,4,5-tetraaminobenzene (BTA) based metal-organic polymer to precisely modulate the electronic state of metal centers. Due to the electron-withdrawing properties of the carbonyl group, metal centers can be converted to an electron-deficient state, fascinating the NO₃⁻ adsorption and promoting continuous hydrogenation reactions to produce NH₃. Compared to CuBTA with a low NO₃⁻-to-NH₃ conversion efficiency of 85.1 %, quinone group functionalization endows the resulting copper tetraminobenzoquinone (CuTABQ) distinguished performance with a much higher NH₃ FE of 97.7 %. This molecular engineering strategy is also universal, as verified by the improved NO₃⁻-to-NH₃ conversion performance on different metal centers, including Co and Ni. Furthermore, the assembled rechargeable Zn−NO₃⁻ battery based on CuTABQ cathode can deliver a high power density of 12.3 mW cm⁻². This work provides advanced insights into the rational design of metal complex catalysts through the molecular-level regulation for NO₃⁻ electroreduction to value-added NH₃.     

稀土“农乐”益植素的增产效果

稀土农用是国家经委要求的推广项目之一。石河子地区经过三年的小区试验和大面积示范,说明在春小麦的苗期、棉花的初花期喷施稀土“农乐”益植素可以收到明显的增产效果和经济效益。     

Optical diagnostics on the reactivity controlled compression ignition (RCCI) with micro direct-injection strategy

Micro direct-injection (DI) strategy is often used to extend the operation range of the reactivity controlled compression ignition (RCCI) to high engine load, but its combustion process has not been well understood. In this study, the ignition and flame development of the micro-DI RCCI strategy were investigated on a light-duty optical engine using formaldehyde planar laser-induced fluorescence (PLIF) and high-speed natural flame luminosity imaging techniques. The premixed fuel was iso-octane and an oxygenated fuel of polyoxymethylene dimethyl ethers (PODE) was employed for DI. The fuel-air equivalence ratio of DI was kept at 0.09 and the premixed equivalence ratio was varied from 0 to 1. RCCI strategies with early and late DI timing at –25° and –5° crank angle after top dead center were studied, respectively. Results indicate that the early micro-DI RCCI features a single-stage high-temperature heat release (HTHR). The combustion in the low-reactivity region shows a combination of flame front propagation and auto-ignition. The late micro-DI RCCI presents a two-stage HTHR. The second-stage HTHR is owing to the combustion in the low-reactivity region that is dominated by flame front propagation when the premixed equivalence ratio approaches 1. For both early and late micro-DI RCCI, the intermediate-temperature heat release (ITHR) of iso-octane, indicated by formaldehyde, takes place in the low-reactivity region before the arrival of the flame front. This is quite different from the flame front propagation in spark-ignition (SI) engine that shows no ITHR in the unburned region. The DI fuel mass is a key factor that affects the combustion in the low-reactivity region. If the DI fuel mass is quite low, there is more possibility of flame front propagation; otherwise, sequential auto-ignition dominates. The emergence of the flame front propagation in micro-DI RCCI strategy reduces its combustion rate and peak pressure rise rate.     

Effect of cation and anion defects on the resistive switching polarity of ZnO x thin films

In this paper, we achieve the resistive switching (RS) polarity from unipolar to bipolar in a simple Al/ZnO _x /Al structure by moderating the oxygen content in the ZnO sputtering process. In a pure Ar sputtering, Al/ZnO _x /Al shows unipolar behavior, as oxygen partial pressure increases, the RS polarity changes to bipolar, and the switch current decreases by about five orders of magnitude. The current transport properties of unipolar device show ohmic behavior under both high resistance (HRS) and low resistance states (LRS), but the bipolar device shows Schottky barrier modulated current transport properties. We study the defect types in the unipolar and bipolar devices through photoluminescence (PL) spectra. The PL results show that the interstitial zinc (Zn_i) and interstitial oxygen (O_i) are dominant in unipolar and bipolar devices, respectively. We attribute this phenomenon to Zn_i and O_i playing important role in unipolar (URS) and bipolar resistive switching (BRS), respectively.     

Hilbert空间中拟非扩张映像族的逼近定理

在Hilbert空间中,设计了一种新算法用以逼近拟非扩张映像族的公共不动点,并利用所提出的算法证明了拟非扩张映像族的公共不动点的逼近定理,所得结果改进和推广了一些最近文献的相关结果.