关键词： 机械设计制造   学院   三峡大学   能源与动力工程   机械电子工程   材料成型   控制工程   本科专业  

摘要： 2014年1月原机械与材料学院更名为机械与动力学院，学院现设有机械设计制造及其自动化、机械电子工程、材料成型及控制工程、工业工程、能源与动力工程、核工程与核技术六个本科专业，其中机械设计制造及其自动化为国家特色专业、第二批卓越工程师教育培养计划专业和省本科品牌专业，材料成型及控制工程为第三批卓越工程师教育培养计划专业。

关键词： growth plate chondrocytes   mechanical strain   yes-associated protein (YAP)   extracellular signal-regulated kinase (ERK)   mechanotransduction  

摘要： Yes-associated protein (YAP) and extracellular signal-regulated kinase (ERK) have been considered as key regulators in tissue homeostasis, organ development, and tumor formation. However, the roles of YAP and ERK in the mediating strain mechanosensing in the growth plate cartilage have not been determined. In this study, chondrocytes obtained from the growth plate cartilage of 2-week-old Sprague-Dawley rats were subjected to the mechanical strain with different magnitudes and durations at a frequency of 0.5Hz. We found that YAP and ERK activation in response to mechanical strain was time and magnitude dependent. Pretreatment with a RhoA inhibitor (C3 toxin) or a microfilament cytoskeleton disrupting reagent (cytochalasin D) could suppress their activation. In addition, activated YAP and ERK were able to induce cell cycle progression by up-regulating the expression of cell cycle-related genes. These results shed new light on the function of YAP and ERK in mechanical strain-promoted growth plate development. Our results also provided evidence that RhoA and cytoskeletal dynamics are required for this mechanotransduction. (c) 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1121-1129, 2016.

关键词： Constraint   Periodic motion   Bifurcation   SC-CNN   Circuit   Hardware implementation  

摘要： A two-degree-of-freedom periodically forced system with multiple motion limiting constraints is considered. The incidence relation between dynamics and key parameters (clearance, constraint stiffness and forcing frequency) is numerically studied by selecting different values of constraint stiffness and finely scanning the (forcing frequency, clearance)-parameter plane. Two cases, associated with the non-prepressing and prepressing constraints, are considered in the research. The fundamental group of impact motions with an excitation period and the different impact number is studied with emphasis on the generation mechanism. The complicated and regular transition characteristics between adjacent fundamental impact motions are analyzed by their existence domains and bifurcation boundaries in the (forcing frequency, clearance)-parameter plane. The influence of the constraint parameters on multiformity and transitional characters of periodic-impact motions of the system is studied in relatively large parameter spaces. An electronic circuit in the framework of state-controlled cellular neural network (SC-CNN) is designed for experimental verification of dynamic mechanical behaviors of the non-smooth system driven by periodical exciting forces. Real electronic circuit, based on four SC-CNN cells, is made by using printed circuit board, and the oscilloscope output of phase portraits of electrical waveforms generated by the circuit itself is experimentally observed. A good agreement among the numerical results of the mechanical model, the electronic design simulation of the circuit and the real oscilloscope outputs of hardware implementation is confirmed. The results fully show that the modeling method using the strategy based on SC-CNN is suitable for the modeling of the periodically forced systems with multiple motion limiting constraints. The high availability and reliability of the electronic circuit, based on the SC-CNN framework, are verified by the contrast analyses.

关键词： Curing characteristics   Thermosetting resin   Molecular dynamics   Mechanical properties  

摘要： We performed molecular dynamics (MD) simulation that includes multidisciplinary characteristics from synthesis to mechanical properties of epoxy resin. First, to reproduce the actual chemical reaction between matrix and curing agents, we conducted curing simulation wherein the activation energy and heat of formation are considered for the chemical reaction. Subsequently, we performed MD simulations using cross-linked structure obtained from curing simulation to derive density and Young's modulus. Results indicated that cross-linked structures involving both activation energy and heat of formation could reproduce experiment results that are evaluated using differential scanning calorimetry (DSC) measurements and mechanical tests. The simulated results imply that electrostatic interaction plays an important role in Young's modulus. The density of the hydrogen bond between the oxygen of the hydroxyl group and the hydrogen atom is a key factor for the difference in Young's modulus for each base resin. These findings confirm that MD simulation is a potential alternative to experiments for the appropriate material selection of epoxy resin. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： Polyoxymethylene   recycled carbon fiber   composites   reinforcement   mechanical properties  

摘要： Recycled carbon fiber (RCF) was employed as a reinforcing material to prepare polyoxymethylene (POM)-based composites through a simple melting extrusion. An effective approach was developed to clean and modify the surface of the as-received RCF with nitric acid and then with a silane coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for POM/RCF composites due to the improved interfacial adhesion between the fibers and the matrix. The thermal stabilities of the composites were also improved in the presence of RCF. The morphological observation of impact fracture surfaces indicated that the RCF gained a homogeneous dispersion in POM matrix due to good interfacial boding between fibers and matrix. The studies on nonisothermal and isothermal crystallization behaviors showed that RCF acted as a nucleation agent for the crystallization of POM domain in composites;therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of RCF. These crystallization features may be advantageous for the enhancement of mechanical performance and processability of POM-based composites.

关键词： Kinetics   Thermogravimetry analysis   Rare earth metals   Thermal decomposition   Solid-state reaction  

摘要： The formation of light rare earth metal oxides such as CeO2, La2O3, Sm2O3, Nd2O3 and Pr2O3 from thermal decomposition of its nitrate precursors (Ce(NO3)(3)center dot 6H(2)O, La(NO3)(3)center dot 6H(2)O, Sm(NO3)(3)center dot 6H(2)O, Nd(NO3)(3)center dot 6H(2)O and Pr(NO3)(3)center dot 6H(2)O) have been investigated by thermogravimetric analysis. The rare earth metal oxides obtained were characterized for the nature of chemical bonds and textural properties using FTIR and N-2-physisorption analyses, respectively. The FTIR analysis of the rare earth metal precursors and the oxides showed that the OH- and NO- bonds depicting the presence of hydrated water molecules and nitrate disappeared after the thermal decomposition leaving out only the pure solid oxides. The kinetics data obtained from the thermogravimetric analysis were fitted into "model free" kinetic expressions such as Kissinger, Ozawa-Flynn-Wall to calculate the apparent activation energy of the solid-state decomposition reaction of the rare earth metal precursors. The kinetic parameters were further analyzed using Coat-Redfern model to determine the possible mechanism of the decomposition process. The calculated values of the activation energy obtained from both Kissinger and Ozawa-Flynn-Wall models were similar compared to that obtained from Coat-Redfern model. Highest activation energies of 230.26, 344.78, 320.2.78, 392.72 and 258.26 kJ mol(-1) were obtained from decomposition of Ce(NO3)(3)center dot 6H(2)O, La(NO3)(3)center dot 6H(2)O, Sm(NO3)(3)center dot 6H(2)O, Nd(NO3)(3)center dot 6H(2)O and Pr(NO3)(3)center dot 6H(2)O), respectively, using Kissinger model, while the analysis of the kinetic data using Ozawa-Flynn-Wall model gave the highest activation energies of 229.01, 350.56, 348.56, 392.72 and 388.56 kJ mol(-1) for decomposition of Ce(NO3)(3)center dot 6H(2)O, La(NO3)(3)center dot 6H(2)O, Sm(NO3)(3)center dot 6H(2)O, Nd(NO3)(3)center dot 6H(2)O and Pr(NO3)(3)center dot 6H(2)O), respectively. Thirte

关键词： Boron nitride nanoribbons   MD simulation   Tersoff potential   Thermal properties   Mechanical property  

摘要： Thermo-mechanical properties of boron nitride nanoribbons (BNNRs) were computed using molecular dynamics simulation with optimized Tersoff empirical potential. Thermal conductivity (TC) and heat transport properties of BNNRs were calculated as functions of both temperature and nanoribbon's length. The results show that TC of BNNRs decreases with raising temperature by T-1.5 up to 1000 K. The phonon-phonon scattering relaxation time, mean free path of phonons, and contribution of high frequency optical phonons in TC of BNNRs were calculated at various temperatures. TC decreases as nanoribbon size increases and it converges to similar to 500 W m(-1)K(-1) for nanoribbons with length longer than 30 nm. The mechanical properties, including Gruneisen parameter, stress-strain response curves, Young's modulus, intrinsic strength, critical strain, and Poisson's ratio were calculated in the temperature range of 137-1000 K. The simulation results show that Gruneisen parameter and poisson's ratio of BNNRs are -0.092 and 0.245, respectively. The Young's modulus of BNNRs decreases with raising temperature and its value is 630 GPa at 300 K. According to the results, BNNRs duo to their extraordinary thermo-mechanical properties, are the promising candidate for the future nano-device manufacturing. (C) 2016 Elsevier Inc. All rights reserved.

关键词： Dynamics (Mechanics)   Machinery   Manufacturing   Proteins   Collapse   Drag (Fluid dynamics)   Rotation  

摘要： Bacteriophage T4 is one of the most common and complex of the tailed viruses that infect host bacteria using an intriguing contractile tail assembly. Despite extensive progress in resolving the structure of T4, the dynamics of the injection machinery remains largely unknown. This paper contributes a first model of the injection machinery that is driven by elastic energy stored in a structure known as the sheath. The sheath is composed of helical strands of protein that suddenly collapse from an energetic, extended conformation prior to infection to a relaxed, contracted conformation during infection. We employ Kirchhoff rod theory to simulate the nonlinear dynamics of a single protein strand coupled to a model for the remainder of the virus, including the coupled translation and rotation of the head (capsid), neck, and tail tube. Doing so provides an important building block toward the future goal of modeling the entire sheath structure which is composed of six interacting helical protein strands. The resulting numerical model exposes fundamental features of the injection machinery including the time scale and energetics of the infection process, the nonlinear conformational change experienced by the sheath, and the contribution of hydrodynamic drag on the head (capsid).

关键词： Osteocytes   Calcium   Endoplasmic reticulum   Fluid flow   Voltage-sensitive calcium channels  

摘要： One of the earliest responses of bone cells to mechanical stimuli is a rise in intracellular calcium (Ca2+), and osteocytes in particular exhibit robust oscillations in Ca2+ when subjected to loading. Previous studies implicate roles for both the endoplasmic reticulum (ER) and T-Type voltage-sensitive calcium channels (VSCC) in these responses, but their interactions or relative contributions have not been studied. By observing Ca2+ dynamics in the cytosol (Ca-cyt(2+)) and the ER (Ca-ER(2+)), the focus of this study was to explore the role of the ER and T-Type channels in Ca2+ signaling in bone cells. We demonstrate that inhibition of T-Type VSCC in osteocytes significantly reduces the number of Ca-cyr(2+) responses and affects Ca-ER(2+) depletion dynamics. Simultaneous observation of Ca2+ exchange among these spaces revealed high synchrony between rises in Ca-cyt(2+) and depressions in Ca-ER(2+), and this synchrony was significantly reduced by challenging T-Type VSCC. We further confirmed that this effect was mediated directly through the ER and not through store-operated Ca2+ entry (SOCE) pathways. Taken together, our data suggests that T-Type VSCC facilitate the recovery of Ca-ER(2+) in osteocytes to sustain mechanically induced Ca2+ oscillations, uncovering a new mechanism underlying the behavior of osteocytes as mechanosensors. (C) 2016 Elsevier Inc. All rights reserved.

关键词： Membrane bioreactor   Mechanical stirring   Membrane fouling   Mixed liquor properties   Hydrodynamic conditions  

摘要： Although membrane bioreactor is widely used in wastewater treatment, the problem of membrane fouling remains to be resolved. This paper focused on the influence of mechanical stirring on membrane fouling. Ammonium removal decreased with viscous bulking when stirring rates slowed down. Transmembrane pressure increased more rapidly when the stirring rate decreased. The resistance of the gel layer increased significantly under low stirring rates, which indicated that the fouling rates of MBR in different stages were attributed to gel layer variation. The proportion of small particles increased when stirring rates slowed down. Furthermore, 16S rRNA gene amplicon sequencing showed that Proteobacteria and Actinobacteria were dominant in the mixed liquor. The relative abundance of Actinobacteria increased from 41% to 50% in the entire experiment. The computational fluid dynamics model was used to simulate the fluid flow characteristics. The model indicated velocities and directions of the fluid flow changes with different stirring rates. (C) 2016 Elsevier Ltd. All rights reserved.