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。

关键词： 种植体周围炎   光动力疗法   机械清创   翻瓣术   Meta分析  

摘要： 目的采用Meta分析方法系统评价光动力疗法(PDT)辅助机械清创(MD)或翻瓣清创术(OFD)治疗种植体周围炎的短期临床疗效。方法计算机检索PubMed、The Cochrane Library、Embase、中国知网、万方及维普等数据库,检索PDT辅助MD或OFD治疗种植体周围炎临床疗效观察的随机对照试验(RCTs),检索时限从建库至2019年6月1日。由2名评价员根据纳入排除标准独立筛选文献,进行文献质量评价、提取数据并交叉核对,采用Revman5.3软件进行统计学分析。结果共纳入9篇RCTs,研究对象544例。Meta分析结果显示,与单独的MD或OFD相比,辅助应用PDT种植体周围炎患者的探诊深度(PD)减少[MD=0.52,95%CI(0.13,0.92),P=0.010]、临床附着丧失(CAL)获得[MD=0.36,95%CI(0.11,0.61),P=0.004]、探诊出血指数(BOP)减少[MD=4.96,95%CI(1.87,8.06),P=0.002]、改良龈沟出血指数(m SBI)降低[MD=0.53,95%CI(0.32,0.73),P<0.00001]更加显著,差异有统计学意义(P<0.05),而改良菌斑指数(m PLI)降低[MD=0.05,95%CI(-0.12,0.22),P=0.55]差异无统计学意义。与辅助局部用药(LDD)相比,辅助应用PDT患者各临床指标差异均无统计学意义(P>0.05)。结论 PDT的辅助应用较单独的机械清创或翻瓣清创治疗种植体周围炎的临床疗效更佳,其效果与局部用药相当。

关键词： 气囊-旋转机械系统   限位器   冲击激励   非线性动力学  

摘要： 主要研究了冲击激励下含限位器的气囊-旋转机械系统的动力学特性。首先,考虑了轴承的非线性油膜力和转子的不平衡力等因素,建立了在冲击激励下气囊-旋转机械系统的非线性动力学模型;然后,采用数值模拟的方法分析了冲击激励下,限位器对气囊-旋转机械系统动力学特性的影响,讨论了在限位器不同刚度比、安装间隙、阻尼比等参数下气囊-旋转机械系统的动力学响应。结果表明:限位器的刚度和安装间隙对冲击激励下系统的最大相对位移和绝对加速度有较大影响,而阻尼对其影响会随着刚度比的增大而减小。

关键词： Adaptive neuro fuzzy inference system modeling   mechanical properties   moisture absorption   natural fibre composites  

摘要： Natural fibres possess low density, less abrasiveness, good strength and sound absorption capacity and its significance lies in being renewable and biodegradable. The mechanical characteristics and moisture absorption of pineapple fibres reinforced with polypropylene resin are focused in this study. Chopped fibres and unidirectional fibre mats of pineapple were reinforced with polypropylene resin to make pineapple fibre/polypropylene composites. The length of the pineapple fibres and the orientation of the layup of the fibre mats are varied to make composite specimens and the mechanical properties are tested. Moisture absorption studies were carried out and it was confirmed to follow Fickian diffusion. A total of 384 samples were tested and it was observed that all the samples reached its saturation in moisture absorption before 720 h and the strength was inversely proportional to the moisture absorbed. Specimens reinforced with unidirectional fibre mats of alternate orientation possessed high strength irrespective of the moisture absorbed when compared to the specimens reinforced with chopped fibres of random orientation. Neuro fuzzy modelling using ANFIS tool box in MATLAB was used to correlate the static mechanical properties of pineapple fibre-reinforced polymer under different moisture conditions, fibre orientations, fibre volume percentage, fibre size, etc.

关键词： Unstable pelvic ring injuries   Hemodynamically unstable   Polytrauma   Temporary pelvic fixation  

摘要： In polytrauma patients with unstable pelvic ring injuries, pelvic binders interfere with femoral arterial access and are frequently removed for emergent endovascular and abdominal procedures. The 'trochanteric C-clamp' (T-clamp) is a novel technique described for rapid stabilization of the pelvis without fluoroscopic imaging, while ensuring adequate access to the groin. This case series reports the feasibility and safety following T-clamp application for unstable pelvic ring injuries in patients requiring simultaneous endovascular intervention. Between May 2018 - May 2019, seventeen patients with unstable pelvic ring injuries were treated with a T-clamp in conjunction with other emergent endovascular or intra-abdominal procedures. Nine presented with unstable APC injuries, seven with unstable LC injuries and one with a vertical shear pattern. Complications related to the T-clamp were prospectively collected. Following T-clamp application, there were two cases of intraoperative over-reduction, one of which required exchange for an anterior external fixator. This was the result of a concomitant acetabulum fracture leading to iatrogenic acetabular protrusion secondary to the T-clamp. Twelve cases maintained the T-clamp fixation postoperatively ranging from 1-3 days. One postoperative loss of reduction was noted and required exchange for anterior external fixator. In hemodynamically unstable patients who require emergent endovascular procedures, such as pelvic angiography and REBOA, T-clamp application offers a reasonably safe and effective method for expeditious stabilization of the pelvis while allowing unimpeded access to the abdomen, groin and pelvis. Caution should also be applied in patients with concomitant acetabulum fracture for risk of malreduction. Additionally, its prolonged postoperative use should be limited to patients who are not immediately suitable for fixation of the pelvis. (C) 2020 Elsevier Ltd. All rights reserved.