关键词： graphene mechanical resonator   phonon-based information processing   coherent oscillation  

摘要： Vibrational modes in mechanical resonators provide a promising candidate to interface and manipulate classical and quantum information. The observation of coherent dynamics between distant mechanical resonators can be a key step toward scalable phonon-based applications. Here we report tunable coherent phonon dynamics with an architecture comprising three graphene mechanical resonators coupled in series, where all resonators can be manipulated by electrical signals on control gates. We demonstrate coherent Rabi oscillations between spatially separated resonators indirectly coupled via an intermediate resonator serving as a phonon cavity. The Rabi frequency fits well with the microwave burst power on the control gate. We also observe Ramsey interference, where the oscillation frequency corresponds to the indirect coupling strength between these resonators. Such coherent processes indicate that information encoded in vibrational modes can be transferred and stored between spatially separated resonators, which can open the venue of on-demand phonon-based information processing.

关键词： Poly(urethane-urea)   Amphiphilic   Self-assembly   Photoisomerization   Dynamic mechanical properties  

摘要： Azobenzene containing polymers have been used in the development of materials and devices responsive to light, devices for optical storage information, with shape-changing and shape-memory capacities, surface-relief grating, holograms, etc. Poly(urethane-urea)s (PUU) based on a hydrophilic polyethylene glycol (PEG-PUU), on a hydrophobic polycaprolactone diol (PCL-PUU) polyols, and on an equimolar mixture of them (PEG/PCL-PUU), 4,4'-diphenylmethane diisocyanate and 4,4'-diaminoazobenzene (DAAB), as a chain extender, were synthesized by a two-step route. PUU were characterized with respect to their chemical structure, molar masses, thermal and dynamic mechanical properties, and spectroscopic properties. The kinetics of the photo- and thermal-induced isomerization were studied in DMF solutions. The isomerization rate constant was two orders of magnitude higher for DAAB compared with PUU in DMF solution, except for PEG/PCL-PUU, for which the rate constant was half the value observed for DAAB. The amphiphilic nature of the PUU resulted in aggregates in DMF and, therefore, the azo isomerization for PEG-PUU and PCL-PUU occurred in a solid-state-like environment. On the other hand, PEG/PCL-PUU presented unimers and aggregates in DMF and the isomerization of azo groups in free PUU chains was faster. The PUU were semicrystalline and thermo-mechanically stable up 150 degrees C due to the hydrogen bonding involving urea, urethane and ester groups. The aggregates size in DMF solution, as well as the dynamic mechanical properties of the PUU, were sensitive to photo- and thermo-induced isomerization.

关键词： Dynamic membrane   Membrane fouling   Natural organic matter   Molecular dynamics simulations   Low-pressure filtration  

摘要： Membrane fouling caused by natural organic matter (NOM) in water is a pressing problem. To address this, heated aluminum oxide particles (HAOPs) have been used as dynamic membranes pre-deposited onto the primary membrane to effectively remove NOM and thereby significantly diminish the fouling potential. An in-depth understanding of the mechanisms underlying the superior performance of HAOPs remains amiss, which motivated this study. Molecular dynamics (MD) simulations were conducted to systematically compare the performance of HAOPs, which have been reported to be particularly effective for high molecular weight (HMW) NOM, with the conventional powdered activated carbon (PAC) adsorbent. Six NOM constituents, three of which have HMW and three have low molecular weight (LMW), were studied. Results indicate that the mechanisms underlying the effective removal of HMW NOM by HAOPs include: (1) higher foulant-HAOPs interaction energy;(2) greater hydration of the HMW NOM, which thereby increases the affinity to the more hydrophilic HAOPs;(3) diminished mobility of the foulant once adsorbed, which deters desorption;and (4) higher peak intensities in the radial distribution functions for multiple functional groups on the HMW NOM foulants. These results are expected to be valuable towards the better design of such materials for mitigating membrane fouling.

关键词： Chemical structure   Nanocomposites   Clay   Materials   Polymers  

摘要： Nacre-mimetic nanocomposites based on high fractions of synthetic high-aspect-ratio nanoclays in combination with polymers are continuously pushing boundaries for advanced material properties, such as high barrier against oxygen, extraordinary mechanical behavior, fire shielding, and glass-like transparency. Additionally, they provide interesting model systems to study polymers under nanoconfinement due to the well-defined layered nanocomposite arrangement. Although the general behavior in terms of forming such layered nanocomposite materials using evaporative self-assembly and controlling the nanoclay gallery spacing by the nanoclay/polymer ratio is understood, some combinations of polymer matrices and nanoclay reinforcement do not comply with the established models. Here, we demonstrate a thorough characterization and analysis of such an unusual polymer/nanoclay pair that falls outside of the general behavior. Poly(ethylene oxide) (PEO) and sodium fluorohectorite form nacre-mimetic, lamellar nanocomposites that are completely transparent and show high mechanical stiffness and high gas barrier, but there is only limited expansion of the nanoclay gallery spacing when adding increasing amounts of polymer. This behavior is maintained for molecular weights of PEO varied over four orders of magnitude and can be traced back to depletion forces. By careful investigation via X-ray diffraction and proton low-resolution solid-state NMR, we are able to quantify the amount of mobile and immobilized polymer species in between the nanoclay galleries and around proposed tactoid stacks embedded in a PEO matrix. We further elucidate the unusual confined polymer dynamics, indicating a relevant role of specific surface interactions.

关键词： HMX/LLM-105 co-crystal   Molecular dynamics(MD) simulation   Binding energy   CED   Bond length   Mechanical properties  

摘要： Based on molecular dynamics (MD) simulation, the binding energy, cohesive energy density (CED), bond length, and mechanical parameters were calculated for 2,6-diamino-3,5-dinitropyrazine-l-oxide (LLM-105) crystal, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal, and their co-crystals under different temperatures. Three LLM-105/HMX patterns were constructed to investigate the influence of component proportion on structures and properties of co-crystals, in which the mole ratios of LLM-105 and HMX are 1:1, 1:2, and 2:1. The effect of temperature and components on the stability and sensitivity were investigated as well. The results show that the binding energies, CED and mechanical parameters of all the co-crystals, decrease when the temperature increases from 248 to 398 K, while their maximum N-NO2 bond length (L-max) increases with rising temperature, indicating that the sensitivities increase and stabilities decrease when temperature rises. At all temperatures, co-crystals exhibit larger CED and shorter bond length than that of single explosive, demonstrating that they are more stable and less sensitive than single crystal, where the stability of co-crystals was ordered as 2:1>1:1>1:2. Moreover, the bulk modulus (K) and shear modulus (G) of co-crystals are lower than that of HMX, conversely, the Cauchy pressure and K/G are higher than that of HMX, implying co-crystals have better ductility. Finally, the 2:1 ratio of LLM-105/HMX co-crystal was identified as the excellent one, owning to the highest binding energy, highest CED, shortest L-max, and greatest ductility. Models of LLM-105/HMX and one of the properties

关键词： Molecular dynamics simulation   potentials   modulus   Poisson ratio  

摘要： As opposed to traditional laboratory testing, Molecular Dynamics (MD) offers an atomistic scale method to estimate the mechanical properties of metals. However, there is limited literature that shows the effect of interatomic potentials when determining mechanical properties. Hence, the present research was conducted to investigate the accuracy of various interatomic potentials in estimating mechanical properties of aluminium. Several types of potentials, including Embedded Atom Method (EAM), Modified EAM (MEAM) and Reactive Force Field (ReaxFF) were compared with available experimental data for pure aluminium to determine the most accurate interatomic potential. A uniaxial tensile test was performed at room temperature using MD simulations for nanoscale aluminium. Results demonstrated that those potentials parameterised with elastic constants at physically realisable temperatures were consistently more accurate. Overall, the Mishin et al. EAM potential was the most accurate when compared to single-crystal experimental values. Regardless of the potential type, the error was significantly higher for those potentials that did not consider elastic constants during development. In brief, the application of the interatomic potentials to estimate mechanical properties of a nanoscale aluminium was investigated.

关键词： 丹参注射液   机械通气   急性肺损伤   血流动力学  

摘要： 目的探讨丹参注射液对急性肺损伤老年患者机械通气后的肺保护疗效以及血流动力学的影响。方法选择2015年11月-2018年11月收治的急性肺损伤老年患者共120例,按随机数字表法分为对照组和观察组,每组均60例,两组患者均给予机械通气。对照组给予常规治疗。观察组在对照组基础上采取丹参注射液静脉滴注,10~20 mL/次,1次/d,连续治疗2周。比较两组血气分析、肺功能、血流动力学。结果治疗2周后,观察组患者的肺泡-动脉氧分压差(AaDO2)、呼吸指数(RI)明显低于对照组以及氧合指数(OI)、用力肺活量(FVC)、第1秒钟用力呼吸量(FEV1)、第1秒用力肺活量占预计值百分比(FEV1%)明显高于对照组(P<0.01);治疗2周后,观察组患者的平均动脉压(MAP)、心率(HR)、心指数(CI)、每搏量指数(SVI)明显高于对照组(P<0.01)。结论丹参注射液能改善急性肺损伤机械通气老年患者的血流动力、动脉血气指标,对肺保护的疗效确切。

关键词： Mechanical activation   Microwave heating   Thermal explosion   High-temperature annealing   Structural relaxation  

摘要： With the use of time-resolved X-Ray diffraction, the analysis of the phase formation dynamics processes in mechanically activated powder mixture of Ti + Al composition in the thermal explosion mode was carried out. The synthesis was conducted under conditions of heating by an external source of constant power. It was found that at the stage of low-temperature heating (preheating stage), a significant amount of reaction products (intermetallic phases) is formed. A possible reason for this is the presence of disordered transition zones that form at the interface between the reactants in the process of preliminary mechanical activation. However, in the process of nonequilibrium synthesis (thermal explosion), the formation of the only compound gamma-TiAl occurs. It was established that the structural changes continue after completion of the chemical reaction. At the first stage of high-temperature annealing, the processes of structural relaxation (which are not accompanied by the appearance of new compounds) are realized. At the second stage, the processes of transition to a thermodynamically equilibrium state occur. It was shown that the forced cooling of the system at various stages of the synthesis can be a way of controlling the structure, composition and, as a consequence, properties of the synthesis product.

关键词： 动力学模型   数学模型推导   机器人建模   重力分析   逆动力学控制  

摘要： 机器人系统建模在布局评估、合理性研究、动画展示以及离线编程等方面有越来越广的应用。文章对两个自由度机械臂基于拉格朗日动力学方程,进行建模。通过建立的模型,分析了重力对两自由度机械臂的影响以及在重力作用下不在稳定位置的机械臂的运动轨迹。基于机械臂的数学模型,基于Simulink仿真环境,建立机械臂的仿真模型。采用逆动力学方法对机械臂进行控制,观察其对机械臂的控制效果[1]。通过仿真建模,可以了解机械臂动力学模型以及机械臂动态模型的控制问题。

关键词： 欠驱动   柔性机械臂   动力学建模   控制律设计   Matlab仿真   结果分析  

摘要： 针对欠驱动柔性机械臂建模、控制困难的问题,文中采用在第一关节安装轻质弹簧的方法来表示机械臂的柔性,从而得到柔性臂的简化模型。将其应用到两连杆欠驱动柔性机械臂中,建立欠驱动柔性机械臂的系统模型,并利用拉格朗日函数法,对该系统进行动力学建模。同时通过构造基于系统能量和驱动杆状态的李雅普诺夫函数,设计该欠驱动柔性机械臂系统的控制律。最后,使用Matlab对该系统及所设计的控制律进行数值仿真。仿真结果表明,所构建的动力学模型以及设计的控制规则具有良好的有效性,且同时具备响应速度快、控制输入小的优点。