关键词： HST   联合试验研究   匹配优化   农用机械  

摘要： 该文针对农用机械静液压传动(Hydrostatic Static Transmission,HST)系统及发动机联合系统的工作特性开展试验研究,经过试验得到不同油门开度及不同分流比例下的发动机输出特性以及HST系统传动特性,对不同工况下动力系统和传动系统的传动损失和泄漏损失进行研究,通过合理的匹配优化,以改进系统的效率。试验结果表明HST系统的传动效率受到动力输入及输出特性和分流比例的综合影响,通过合理的设计动力匹配,在分流比例为25%时,HST系统机械损失和泄漏损失减少,发动机与HST耦合系统效率可达80%以上,个别工况效率超过90%,比传统的静液压传动系统提高10%左右的效率,能够提高农用机械整体系统的效率,获得良好的系统动力性和燃油经济性。

关键词： Nanocrystalline structure   amorphous structure   gold   nanowire   molecular dynamics  

摘要： The effects of microstructure and loading mode on the mechanical properties of Au nanowires (NWs) are studied using molecular dynamics simulations based on the many-body embedded-atom potential. The effects are investigated in terms of common neighbour analysis, shear strain distribution, and stress-strain curves. The microstructure effect is examined using single-crystalline (SC), nanocrystalline (NC), and amorphous (AC) structures. The simulation results show that during tension, SC, NC, and AC NWs have visually similar deformations and similar ultimate strains, but completely different deformation mechanisms. For all loading modes, the SC NWs have the highest tensile and shear strength values and the NC NWs have the highest compressive strength. The AC NWs have poor strength under tensile, compressive, and shear loadings. The presence of grain boundaries increases the geometric instability of the NC NWs under compression and shear loadings.

关键词： 六自由度机械臂   Newton-Euler法   动力学   流体阻力  

摘要： 针对应用于深水环境的六自由度水下机械臂,首次基于迭代Newton-Euler矢量力学方法和Morison方程建立了静水条件下考虑流体阻力的六自由度机械臂动力学模型,得到了各关节流体拖曳力矩和附加质量力矩的解析表达式,进而推导获得了各关节的驱动力矩和水阻力矩解析表达式.通过Matlab软件仿真分析了流体阻力对机械臂关节控制力矩的最大影响可达8.69%,结果表明流体阻力对机械臂的影响是不可忽视的.在某些水下高精度作业的情况下,应用文中提出的考虑流体阻力影响的六自由度机械臂动力学模型可以获得更高的机械臂控制精度.

关键词： Epoxy resin   PEEK microparticles   Curing kinetics   Mechanical properties  

摘要： In this paper, a polyether-ether-ketone (PEEK)/epoxy composite was prepared by using PEEK microparticles as the reinforcement. The nonisothermal differential scanning calorimetry (DSC) test was used to evaluate the curing reaction of PEEK/epoxy resin system. The curing kinetics of this system were examined utilizing nonisothermal kinetic analyses (Kissinger and Ozawa), isoconversional methods (Flynn-Wall-Ozawa and KissingerAkahira-Sunose) and an autocatalytic reaction model. During these analyses, the kinetic parameters and models were obtained, the curing behavior of PEEK/epoxy resin system under dynamic conditions was predicted. The results show that isoconversional methods can adequately interpret the curing behavior of PEEK/epoxy resin system and that the theoretical DSC curves calculated by the autocatalytic reaction model are in good agreement with experimental data. Furthermore, the tensile elongation at break, tensile strength, flexural strength, compression strength and compression modulus increased by 81.6%, 33.66%, 36.53%, 10.98% and 15.14%, respectively, when PEEK microparticles were added in epoxy resin composites.

摘要： We present a case of abdominal aortic aneurysm open repair planned with temporary left ventricular support (Impella (R)) in a patient suffering from severe chronic heart failure. Only 1 single similar case was reported in the literature from 1974.

关键词： Metallic glasses   Molecular dynamics   Coordination numbers   Strain-rate  

摘要： Using molecular dynamics simulations with the embedded atomic method (EAM) to describe interatomic interactions, structural and mechanical properties of Mg-Al metallic glasses (MG) have been investigated for different compositions. The atomic structure is characterized using various techniques such as the Radial Distribution Function (RDF), the Voronoi Tessellation Analysis (VTA) and coordination number (CN) distribution. The results confirmed that the Mg-Al glass formation is accompanied by a splitting of the RDF second peak upon cooling process. The glass transition temperature is determined using different method involving a new suggested way consisting of the cross-over between low and high coordination numbers curves during cooling process. This last technique gives approximate results that converge to those given by classical methods. On the other hand, we applied a strain-rate of 10(10) s(-1) at 300 K and showed that with the increase of Al composition, the maximal stress increases as a function of strain. For a fixed composition of Mg-Al MG, the yield strength increases with the increase of strain-rate between 10(9) s(-1) and 10(10) s(-1). The impact of temperature on the mechanical behaviour of Mg-Al under various strain-rates has been investigated and the result suggests that for the same applied strain-rate, the ultimate tensile strength decreases as a function of temperature. Finally, the annealing effect has led to a softening of elastic moduli especially the Young modulus (E) which has been determined through both elastic constants C-ij and from the stress-strain curve.

关键词： Ordinary Portland cement   Retarder   Maltodextrin   Hydration kinetics   Adsorption  

摘要： In this study, the effect of maltodextrin on the hydration kinetics of ordinary Portland cement was investigated. Additionally, the impact of maltodextrin on the physical and mechanical properties of cement is further studied via setting time, fluidity and mechanical strength tests which has been conducted with different curing times (16 h, 1 d, 3 d, 28 d). The results revealed the impact on the mechanical properties of OPC is dosage and time dependent. At the early curing time of 16 h, the addition of maltodextrin decreased the compressive strength of all mortar samples substantially;a higher dosage of maltodextrin resulted in even lower compressive strength. However, at extended curing times such as 1 d, 3 d or 28 d, the impact on the compressive strength of OPC is dependent on dosage: relatively low dosages (0.01-0.05%) of maltodextrin increased the compressive strength of mortar, whereas higher dosages (>= 0.1%) of maltodextrin was found to decrease the compressive strength of mortar. Furthermore, the time - dependent development of hydration products was monitored via in-situ XRD at the different ages of cement hydration. The results showed that the addition of maltodextrin delays cement hydration which results in less hydration products like Portlandite and ettringite. Finally, the mode of interaction between maltodextrin and cement was assessed through adsorption and zeta potential measurements. The adsorption as well as zeta potential measurements confirm that the retarding mechanism of maltodextrin relies on adsorption on the surface of cement particles.

关键词： diabetes mellitus   quantitative systems pharmacology   SGLT2   1 selectivity   sodium‐   dependent glucose transporter   systemic glucose dynamics  

摘要： Sodium-dependent glucose transporter (SGLT) 2 is specifically expressed in the kidney, while SGLT1 is present in the kidneys and small intestine. SGLT2 inhibitors are a class of oral antidiabetic drugs that lower elevated plasma glucose levels by promoting the urinary excretion of excess glucose through the inhibition of renal glucose reuptake. The inhibition selectivity for SGLT2 over SGLT1 (SGLT2/1 selectivity) of marketed SGLT2 inhibitors is diverse, while SGLT2/1 selectivity of canagliflozin is relatively low. Although canagliflozin suppresses postprandial glucose levels, the degree of contribution for SGLT1 inhibition to this effect remains unproven. To analyze the effect of SGLT2 inhibitors on postprandial glucose level, we constructed a novel quantitative systems pharmacology (QSP) model, called human systemic glucose dynamics (HSGD) model, integrating intestinal absorption, metabolism, and renal reabsorption of glucose. This HSGD model reproduced the postprandial plasma glucose concentration-time profiles during a meal tolerance test under different clinical trial conditions. Simulations after canagliflozin administration showed a dose-dependent delay of time (T-max,T-glc) to reach maximum concentration of glucose (C-max,C-glc), and the delay of T-max,T-glc disappeared when inhibition of SGLT1 was negated. In addition, contribution ratio of intestinal SGLT1 inhibition to the decrease in C-max,C-glc was estimated to be 23%-28%, when 100 and 300 mg of canagliflozin are administered. This HSGD model enabled us to provide the partial contribution of intestinal SGLT1 inhibition to the improvement of postprandial hyperglycemia as well as to quantitatively describe the plasma glucose dynamics following SGLT2 inhibitors.

关键词： Polymer-metal multilayers   Ballistic impact resistance   High strain rates   Energy dissipation   Dislocation nucleation and recovery   Molecular dynamics  

摘要： Recent microprojectile impact tests have revealed that ultra-thin polymer films possess superior specific penetration energy, about ten times more than that of conventional armour materials. On the other hand, it is well established that metallic nanostructures demonstrate extraordinary mechanical properties. Therefore, it may be possible to achieve structures with superior dynamic performance by arranging ultrathin polymer and metal films in multilayer architectures. In order to test this hypothesis, we conducted molecular dynamics simulations of ballistic impact tests of multilayer aluminium-polyurea nanostructures. The computed specific penetration energy of a polymer-metal bilayer is 42% higher than the highest experimentally measured value for any material at a similar impact speed. Moreover, an aluminium layer confined between two polyurea layers has approximately 40% less impact-induced dislocations compared to an aluminium layer which is in contact with only one polyurea layer. This observation clearly demonstrates that the polymer exerts remarkable resistance on the dislocation nucleation in the metallic layer. Our results propose a potential bottom-up design pathway to develop structures with superior dynamic performance.

关键词： Phosphorene   Kirigami   Flexibility   Molecular dynamics  

摘要： The newly discovered two-dimensional phosphorene suffers low stretchability which limits its application in flexible devices. Herein we employ kirigami technique to overcome this limitation. Molecular dynamics simulation is employed to investigate the mechanical properties of kirigami-phosphorene under shear and tensile loadings. Our simulation results show that loading type, intrinsic structural anisotropy, and the height of middle cuts are three key factors that govern the mechanical response of kirigami-phosphorene. Under the tensile loading along the armchair direction, phosphorene exhibits a considerable increase in its tensile strain. By contrast, phosphorene is too weak to stand any structural modification induced by kirigami in the zigzag direction. Under shear loading, there is merely no improvement in the shear properties of kirigami-phosphorene. Our results demonstrate the prospective applications of kirigami-phosphorene along the armchair direction in modern wearable, and stretchable electronics and optoelectronics devices. (C) 2020 Elsevier B.V. All rights reserved.