关键词： 机械动力传动系统   关键部件   故障预测  

摘要： 工程机械广泛应用于国民经济各行业。要想实现工程机械充分发挥其建设价值,一个重要方面是机械故障检测和维修措施。当前,科学技术的不断进步和革新,为各行业的发展提供了更多的契机,但是,在工程机械使用频率和范围逐渐提高和扩大的背景下,其出现故障的可能性也有提升。工程机械故障检测和维修是工程建设行业发展的关键性保障。在机械设备的应用过程中,尤其是在机械设备的管理实践中,应该全面分析机械修理维护中存在的问题,明确机械设备修理维护的意义,全方位提升机械设备的整体性能。

关键词： 高血压,肺性   通气机,机械   血流动力学   细胞因子类  

摘要： 目的探讨机械通气联合西地那非用于新生儿持续性肺动脉高压(PPHN)治疗的临床效果及对相关指标的影响。方法收集2016年8月至2018年8月在南京中医药大学徐州中心医院儿科接受治疗的68例PPHN患儿,分为对照组(n=34)和观察组(n=34),对照组在常规治疗基础上给予机械通气+硫酸镁治疗,观察组在常规治疗的基础上给予机械通气+西地那非治疗,观察2组血浆细胞因子水平、血流动力学指标变化情况等。结果观察组平均吸氧时间、住院时间均显著短于对照组(t=7.946、10.307,P <0.05);与对照组比较,治疗后观察组收缩期肺动脉压、肺动脉压力、肺血管阻力、体血管阻力水平均显著减低(t=11.579、24.081、6.735、2.946,P均<0.05),体循环收缩压显著升高(t=11.579、5.931,P <0.05);观察组治疗后B型尿钠肽、内皮素1、肿瘤坏死因子α及白介素8均显著低于对照组(t=34.744、6.886、15.873、11.036,P均<0.05),血管紧张素1显著高于对照组(t=5.931,P <0.05);观察组治疗总有效率高于对照组[97.06%(33/34)vs 82.35%(28/34),χ^2=5.100,P=0.023]、并发症总发生率低于对照组[8.82%(3/34) vs 29.41%(10/34),χ^2=4.660,P=0.030]。结论常频机械通气联合西地那非治疗PPHN患儿,可使患儿血流动力学、血浆细胞因子获得更好调节,能够明显效提高总体治疗效果。

关键词： 装载机   凯斯   甲烷动力  

摘要： 2019年4月8日,在德国慕尼黑举行的bauma展上,凯斯纽荷兰工业集团旗下品牌凯斯工程机械发布了甲烷动力概念轮式装载机TETRA,让公众洞见了工程机械在可持续发展、人机互联和技术进步方面的未来。

关键词： Nanostructured materials  

摘要： Abstract: The kinetics of reduction of α-Fe2O3 nanopowder with hydrogen in an electromagnetic field with power mechanical treatment (PMT) in a vortex layer of ferromagnetic particles rotating in the field has been investigated. The kinetic parameters are calculated under the conditions of linear heating and isothermal conditions in accordance with the Freeman–Carroll and McKewan models, respectively. It is established that the electromagnetic field reduces the rate of reduction of the α-Fe2O3 nanopowder to 19% at 400°C, and PMT in a vortex layer intensifies the reduction process up to 4 times. The properties of the starting material and reduction products are studied using the thermogravimetry, X-ray diffraction, and electron microscopy methods. © 2019, Pleiades Publishing, Ltd.

关键词： 空间算子代数   冗余空间机械臂   避障控制   最小距离   躲避速度  

摘要： 研究冗余机械臂的高效率高精度避障控制,针对传统避障算法的不足,要求在保证末端作动器位置精度的同时提高机械臂避障算法的计算效率,提出一种基于空间算子代数的冗余机械臂多障碍物避障控制算法。利用空间算子符号简化机械臂雅克比复杂性,提高程式化,并且通过测算各个障碍物与机械臂之间的最小距离,采用雅克比转置矩阵得到各个杆件的躲避速度,并将躲避速度引入梯度投影法求得操作臂的关节角速度,结合对末端作动器的位置的跟踪控制实现机械臂的避障控制。利用Adams软件建立七自由度机械臂模型验证了算法的有效性。由仿真结果表明,上述控制方法能实现算法计算效率与自由度同阶且保证末端作动器位置精度的机械臂避障控制。

关键词： Mechanical model   Abrasive   Chemical mechanical polishing   Molecular dynamics simulation  

摘要： The loading process among the silicon substrate, silica cluster and polyurethane pad was performed by molecular dynamics simulations. The results showed that the interaction force between the cluster and pad did not change with the working pressure at low load stage due to strong fluidity of pad atoms. But at high load stage, the interaction force would increase with increase of the working pressure owing to the reduction of pad fluidity. These demonstrate that the contact status between the abrasives and pad will change from an elastic contact to plastic contact with increase of working pressure for a chemical mechanical polishing (CMP) process. Finally, a unified mechanical model for the single abrasive during CMP under different loads was established.

关键词： Graphene  

摘要： We investigate the mechanical properties of penta-graphene (PG), a recently proposed two-dimensional carbon allotrope using atomistic simulation techniques combined with the empirical description of interatomic interactions. We report on the dependence of its three in-plane mechanical moduli (i. e. Young's modulus, Poisson's ratio and shear modulus) on the deformation direction, strain and temperature. We show that PG displays a strongly manifested mechanical anisotropy, being characterized by Poisson's ratio and the shear modulus which both depend strongly on the deformation direction. By analyzing bond energies we study the influence of different carbon-carbon bonds on the mechanical response of PG and based on that we explain the origins of the observed anisotropy. We show that it is mostly a consequence of the characteristics of the sp(3)-hybridizied bonds, which form the diamond-like tetrahedral blocks. We investigate the auxeticity of PG in detail and show that it displays complete auxetic behavior, having negative Poisson's ratio for all the deformation directions. We show that the auxeticity of PG is similar to that of defective graphene containing 5-8-5 double vacancies, as it also originates from the so-called de-wrinkling mechanism. We study the influence of temperature and show that it only slightly affects the mechanical moduli of PG. (c) 2019 Elsevier Ltd. All rights reserved.

关键词： Polyanion   Methylene blue   Adsorbent recovery   Thermal degradation kinetics   SEM-EDX  

摘要： Molecular polyanion ammonium heptamolybdatetetrahydrate [(NH4)(6)(Mo7O24)]center dot 4H(2)O (AHMT) was used to remove methylene blue (MB) dye from an aqueous solution through adsorption technique. Due to an electrostatic interaction of MB cation and AHMT anion adsorption take place. AHMT and MB adsorbed AHMT named as MB-AHMT was characterized by FT-IR, PXRD, SEM and SEM-EDX techniques. Specific surface area (22.175 m(2) g(-1)) and pore volume (0.059 cm(3) g(-1)) of AHMT was analyzed by BET analysis. The thermal stability and thermal degradation kinetics of adsorbent were assessed by the thermogravimetric curves recorded at different heating rates. The adsorption equilibrium and kinetic studies indicate that adsorption follows with pseudo first order (R > 0.9998) rather than pseudo second order. Temperature variation study indicates that adsorption was spontaneous, exothermic and entropy increased processes. Experimental data fitted well with Langmuir rather than Freundlich isotherm with maximum adsorption capacity of 877.19 mg g(-1). Excess AHMT was recovered as salt of TBA-AHMT which was characterized by FT-IR spectroscopy. The investigations indicate that AHMT may be a prospective material for the removal of MB dye from polluted water.

关键词： Epoxy resin   Aminoacid   Nanocomposites   Curing   Thermal and mechanical properties  

摘要： In this study, novel spirobiindane based tetrafunctional epoxy resin (SBIE) was synthesized using 3,3,3',3'-tetramethyl-1,1'-spirobiindane-5,5',6,6'-tetraol reacting with epichlorohydrin. The molecular structure of the synthesized resin was characterized by Fourier transform infrared spectra (FTIR) and H-1 and C-13 Nuclear magnetic resonance spectra (NMR). The blends of SBIE with different proportions (2, 4, 6, 8 and 10 wt%) of montmorrilonite nanoclay (MMT) were prepared using ultrasonication process. The quality of dispersion and intercalation/exfoliation of the cured epoxy nanocomposites were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) studies. The curing reactions between SBIE and tryptophan, as an environmentally friendly curing agent, in the presence of 2,4,5-triphenylimidazole together with their nanocomposites including MMT were examined. Curing kinetic studies of the SBIE epoxy matrix and nanocomposites were characterized by differential scanning calorimetry (DSC) at different heating rates (10, 20 and 30 degrees C/min). Flynn-Wall-Ozava (FWO) and Vyzovkin (VYZ) methods were used to calculate the activation energies (Ea). The thermal degradation behaviour of the cured nanocomposites was investigated by using a thermogravimetric analyser (TGA). Moreover, the lap joint shear bonding strengths of SBIE/MMT nanocomposites were investigated. It was found that a significant improvement in thermomechanical performance of the resultant epoxy nano composites was obtained when compared to those of the neat epoxy matrices. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Thiazole   Triazole   Acetamides   Tyrosinase   Melanogenesis   Hemolytic   Binding energy  

摘要： The present research was designed for the selective synthesis of novel bi-heterocyclic acetamides, 9a-n, and their tyrosinase inhibition to overwhelm the problem of melanogenesis. The structures of newly synthesized compounds were confirmed by spectral techniques such as H-1 NMR, C-13 NMR, and EI-MS along with elemental analysis. The inhibitory effects of these bi-heterocyclic acetamides (9a-n) were evaluated against tyrosinase and all these molecules were recognized as potent inhibitors relative to the standard used. The Kinetics mechanism was analyzed by Lineweaver-Burk plots which explored that compound, 9h, inhibited tyrosinase competitively by forming an enzyme-inhibitor complex. The inhibition constants K-i calculated from Dixon plots for this compound was 0.0027 mu M. The computational study was coherent with the experimental records and these ligands exhibited good binding energy values (kcal/mol). The hemolytic analysis revealed their mild cytotoxicity towards red blood cell membranes and hence, these molecules can be pondered as nontoxic medicinal scaffolds for skin pigmentation and related disorders.