介观尺度流体绕流球体的耗散粒子动力学模拟

采用耗散粒子动力学(dissipative particle dynamics, DPD)方法, 对两平行平板间流体绕流三维球体进行了计算. 球体和平行平板由达到平衡状态的冻结DPD粒子组成, 流体在不同无量纲外力驱动下流动, 球体受力由组成球体的所有冻结DPD粒子求和得到. 流动达到充分发展后, 输出球体在流动方向的受力, 并计算球体的阻力系数, 与文献中的关联式进行了对比. 结果表明, 在Re≤qslant 100的范围内, DPD方法能较准确地计算出阻力系数, 在较大雷诺数时, 由于流体的压缩性导致计算结果出现差异.     

Effects of Nb substitution for Zr on the phases,microstructure and magnetic properties of Co80Zr18−xNbxB2 melt-spun ribbons

The phases, microstructure, and magnetic properties of Co₈₀Zr_18−xNb_xB₂ (x=1, 2, 3, and 4) melt-spun ribbons were investigated. The small substitution of Nb for Zr in the Co–Zr–B melt-spun ribbons resulted in the improvement of magnetic properties, especially the coercivity. The main effect of added Nb on the coercovity of Co–Zr–Nb–B melt-spun ribbons, originated from modification of the grain size of Co₁₁Zr₂ phase. The coercivity of the Co–Zr–Nb–B melt-spun ribbons depends on the annealing temperature. The optimal magnetic properties of H_c=5.1 kOe, and (BH)_max=3.4 MGOe were obtained in the Co₈₀Zr₁₅Nb₃B₂ melt-spun ribbons annealed at 600 °C for 3 min.     

Structural characterization of β-V2O5 films prepared by DC reactive magnetron sputtering

β-V₂O₅ films were successfully prepared on silicon substrates by direct current (DC) reactive magnetron sputtering. X-ray diffraction (XRD), Raman spectra and field emission scan electron spectroscopy (SEM) were used to characterize the samples. Results revealed that the deposition temperature significantly influenced on the crystal structure of V₂O₅ films in the growth process. When the deposition temperature was below 500 °C, the sputtered film exhibited the α-V₂O₅ structure. However, β-V₂O₅ film was successfully obtained at 550 °C. High deposition temperature might provide V and O ions high mobility and energy in the reactive sputtering process, which induced the metastable β-V₂O₅ phase formed. The thermal stability of β-V₂O₅ film was studied by micro-Raman spectroscopy. The structure of sputtered β-V₂O₅ film was unstable under high temperature conditions (beyond 500 °C).     

Stress induced preferred orientation and phase transition for ternary WCxNy thin films

We deposit ternary WC_xN_y thin films on Si (1 0 0) substrates at 500 °C using direct current (DC) reactive magnetron sputtering in a mixture of CH₄/N₂/Ar discharge, and explore the effects of substrate bias (V_b) on the intrinsic stress, preferred orientation and phase transition for the obtained films by virtue of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and selective area electron diffraction (SAED). We find that with increasing the absolute value of V_b up to 200 V the carbon (x) and nitrogen (y) atom concentrations of WC_xN_y films keep almost constant with the values of 0.75 and 0.25, respectively. The XPS and SAED results, combined with the density-functional theory (DFT) calculations on the electronic structure of WC_0.75N_0.25, show our obtained WC_xN_y films are single-phase of carbonitrides. Furthermore, we find that the compressive stress sharply increases with increasing the absolute value of V_b, which leads to a pronounced change in the preferred orientation and phase structure for the film, in which a phase transition from cubic β-WC_xN_y to hexagonal α-WC_xN_y occurs as V_b is in the range of −40 to −120 V. In order to reveal the relationship between the stress and phase transition as well as preferred orientation, the DFT calculations are used to obtain the elastic constants for β-WC_xN_y and α-WC_xN_y. The calculated results show that the preferred orientation is dependent on the competition between strain energy and surface energy, and the phase transition can be attributed to a decrease in the strain energy.     

Synergistic degradation of methyl orange in an ultrasound intensified photocatalytic reactor

An original ultrasound (US) directly intensified photocatalytic reactor was designed to degrade azo dye pollutant methyl orange (MeO) using Degussa TiO(2) as the photocatalyst. The sonolytic, photocatalytic and sonophotocatalytic degradation of MeO in the new reactor and the synergistic effect between sonolysis and photocatalysis were investigated. Effects of operation parameters i.e., US power, TiO(2) dosage, liquid circulation velocity and air flow rate on degradation efficiency were investigated and optimized. The results showed that all parameters have optimal values for the sonophotocatalytic degradation of MeO, and the optimum conditions for the new process are US power 600 W, TiO(2) dosage 3g/L, liquid circulation velocity 4.05×10(-2) m/s and air flow rate 0.2 L/min. Under the optimum conditions, 91.52% MeO had been degraded within 1h, and the combination of sonolysis and TiO(2) photocatalysis exhibited an obvious synergetic effect.     

Room-temperature direct-bandgap photoluminescence from strain-compensated Ge/SiGe multiple quantum wells on silicon

Strain-compensated Ge/Si_0.15Ge_0.85 multiple quantum wells were grown on an Si_0.1>Ge_0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition technology on an n⁺-Si(001) substrate. Photoluminescence measurements were performed at room temperature, and the quantum confinement effect of the direct-bandgap transitions of a Ge quantum well was observed, which is in good agreement with the calculated results. The luminescence mechanism was discussed by recombination rate analysis and the temperature dependence of the luminescence spectrum.     

Electronic transport properties of zigzag carbon- and boron-nitride-nanotube heterostructures

Using first-principles density functional theory and non-equilibrium Green's function formalism for quantum transport calculation, we have investigated the electronic transport properties of heteronanotubes by joining a zigzag (6,0) carbon nanotube and a zigzag (6,0) boron nitride nanotube with different atomic compositions and joint configurations. Our results show that the atomic composition and joint configuration affect strongly the electronic transport properties. Obvious negative differential resistance behavior and large rectifying behavior are obtained in the heterostructure with certain composition and joint configuration. Moreover, tube length and tube radius can affect strongly the observed NDR and rectifying behaviors. The observed negative differential resistance and rectifying behaviors are explained in terms of the evolution of the transmission spectrum with applied bias combined with molecular projected self-consistent Hamiltonian states analysis.     

Multi-stacked organic light-emitting diodes using zinc oxide nanoparticle interfacial layers

Stacked organic light-emitting diodes (SOLEDs) with 30-nm nanoparticle (NP) interfacial layers were investigated. Zinc oxide (ZnO) was used as an interfacial layer between two green polymer (GP) layers. SOLEDs with NP interfacial layers had higher device efficiency than did a single-unit device due to the high probability of exciton recombination that originated from the Auger electron-assisted energy up-conversion process. Although the current density and luminance of SOLEDs with ZnO NP interfacial layers were smaller than those of the reference device, the efficiency was doubled because of the big band alignment difference and the large band gap between GP and ZnO NP interfacial layers, which induced more radiative-exciton recombination.     

Quantum information splitting of an arbitrary three-qubit state via the cavity input–output process

We propose a realizable quantum information splitting (QIS) scheme for an arbitrary three-qubit state via the cavity input–output process. In our scheme, a four-qubit cluster state and a three-qubit Greenberger–Horne–Zeilinge (GHZ) state are used as quantum channel. The sender and controller only need to perform Bell-state measurements and a single-qubit measurement, respectively. The receiver can reconstruct the arbitrary three-qubit state by classical communication and local operations. Compared with the scheme in Nie et al. [Optics Communications 284 (2011) 1457], the quantum resources and classical information in our scheme are decreased by 5 qubits and 1 bit, respectively. Moreover, we replace the W-state category measurement in the former with Bell-state measurements and a single-qubit measurement, which is more simple and feasible in experiment.     

如何通过测量复摆的周期计算转动惯量

本文给出一种简约可行的方法,用来计算不规则物体绕任意轴转动时的转动惯量,同时,亦可定出质心轴位置.本文讨论的内容对教学有意义.