关键词： 振动与波   柔性机械臂   模态分析   弹性变形   动力学建模   振动分析  

摘要： 以仿人手臂的三旋转关节刚柔耦合机械臂为研究对象,对柔性部分建立理论模型并分析其动态特性。为了提高模型精确度,利用有限段方法分析研究不同边界条件下柔性臂各阶固有频率及振型函数,通过假设模态法和汉密尔顿原理,考虑重力,建立机械臂柔性部分动力学模型。引入角度轨迹,在Matlab中利用四阶Runge-Kutta法求解非线性时变微分方程组,获得柔性臂末端负载的残余振动。为实现柔性机械臂模型的进一步精确化和主动残余振动控制提供参考。

关键词： 12-Lead Electrocardiogram   Cardiac MRI   High-field MRI   ECG   MHD   Mechanical activation   Orientation   Magnetohydrodynamic  

摘要： To explore use of the Magnetohydrodynamic Voltage (VMHD), observed in intra-MRI 12-lead electrocardiograms (ECG), to indicate the timing of the onset of left-ventricular mechanical activation (LVMA) and the orientation of the aortic-arch (AAO). Blood flow through the aortic arch during systole, in the presence of the MRI magnetic field (B (0)), generates VMHD. Since the magnitude and direction of VMHD are determined by the timing and directionality of blood flow relative to B (0), we hypothesized that clinically useful measures, LVMA and AAO, could be extracted from temporal and vectorial VMHD characteristics. VMHD signals were extracted from 12-lead ECG traces by comparing traces obtained inside and outside the MRI scanner. VMHD was converted into the Vectorcardiogram frame of reference. LVMA was quantified in 1 subject at 1.5T and 3 subjects at 3T, and the result compared to CINE MRI. AAO was inferred for 4 subjects at 3T and compared to anatomical imaging of the aortic arch orientation in the transverse plane. A < 10% error was observed in LVMA measurements, while a < 3A degrees error was observed in aortic arch orientation measurements. The temporal and vectorial nature of VMHD is useful in estimating these clinically relevant parameters.

关键词： nickel-based single crystal superalloy   Kear-Wilsdorf lock   discrete dislocation dynamics   flow strength anomaly   tension-compression asymmetry  

摘要： Unlike common single crystals, the nickel-based single crystal superalloy shows surprisingly anomalous flow strength (i.e. with the increase of temperature, the yield strength first increases to a peak value and then decreases) and tension-compression (TC) asymmetry. A comprehensive three-dimensional discrete dislocation dynamics (3D-DDD) procedure was developed to model these abnormal mechanical properties. For this purpose, a series of complicated dynamic evolution details of Kear-Wilsdorf (KW) locks, which are closely related to the flow strength anomaly and TC asymmetry, were incorporated into this 3D-DDD framework. Moreover, the activation of the cubic slip system, which is the origin of the decrease in yield strength with increasing temperature at relatively high temperatures, was especially taken into account by introducing a competition criterion between the unlocking of the KW locks and the activation of the cubic slip system. To test our framework, a series of 3D-DDD simulations were performed on a representative volume cell model with a cuboidal Ni3Al precipitate phase embedded in a nickel matrix. Results show that the present 3D-DDD procedure can successfully capture the dynamic evolution of KW locks, the flow strength anomaly and TC asymmetry. Then, the underlying dislocation mechanisms leading to these abnormal mechanical responses were investigated and discussed in detail. Finally, a cyclic deformation of the nickel-based single crystal superalloy was modeled by using the present DDD model, with a special focus on the influence of KW locks on the Bauschinger effect and cyclic softening.

关键词： E. coli biofilms   Mechanical stability   Water jet   Laboratory screening   Hydrodynamic shear  

摘要： The desire to attain a deeper understanding of the fundamental aspects governing the mechanical properties of biofilms has become more prominent in recent years. This has largely been due to the realization that these sessile microbial communities often withstand environments where hydrodynamic turbulence and shearing forces are considerable. In the present study, Escherichia coli K-12 was used as a model system to develop a laboratory technique that can be used to quickly screen the mechanical integrity or stability of laboratory cultivated bacterial biofilms when exposed to such external, hydrodynamic shear forces. The screening method utilizes a custom-built, automated water jetting apparatus to generate and precisely apply a pressurized stream of water directly to biofilms cultured in multi-well plates. An optimized set of water jetting parameters was determined to resolve subtle to moderate differences in the mechanical stability of isogenic strains of E. coli K-12 as a function of percent biofilm removal. Mutations in both flagella biosynthesis (fliA) and acetate metabolism (ackA and ackA pta) were shown to impair the mechanical integrity of 24-h biofilms, while a housekeeping strain deficient in arginine metabolism (argD) exhibited a mechanical stability profile comparable to the parent strain.

关键词： Transition metal ions   montmorillonite   polylactic acid   thermogravimetric analysis   differential scanning calorimetry  

摘要： Polylactic acid nanocomposite was prepared by melt blending polylactic acid (PLA) and transition metal ion (TMI)-modified montmorillonite (MMT;TMI-MMT) using a co-rotating conical twin-screw microcompounder attached with a mini injection moulder. MMT was modified by ion exchange reaction using TMI. Intercalation morphology of TMI on MMT was investigated by x-ray diffraction (XRD) and transmission electron microscopic analyses. XRD patterns indicated penetration of the metal ions into the MMT interlayer and formation of intercalated structure. In order to increase the adsorbed amount of Zn2+ and Cu2+ ions, MMT was previously intercalated with ethylene diamine. Thermogravimetric analysis indicated an increase in the onset of degradation temperature of nanocomposites when compared with virgin PLA. The isothermal cold crystallization kinetics of PLA/TMI-MMT nanocomposites was investigated by differential scanning calorimetry in the temperature range of 100-120 degrees C and the development of relative crystallinity with the crystallization time was analyzed by the Avrami equation. PLA nanocomposites reinforced with TMI-MMT showed a significant increase in tensile and flexural modulus and impact strength when compared with virgin PLA. The flammability studies of PLA/TMI-MMT nanocomposites displayed slow rate of burning and enhanced carbonaceous char formation when compared with virgin PLA matrix.

关键词： caspase-9   glutathione   mitochondrial fission   mitophagy   proliferating cell nuclear antigen   protein carbonyls  

摘要： Doxorubicin (Dox) is an effective chemotherapeutic agent, but known to cause cardiac and hepatic toxicity. Mechanisms of toxicity have not been clearly identified, but shown to involve oxidative stress and mitochondrial dysfunction. However, antioxidant supplementation has only shown modest protection from Dox-induced toxicity in clinical trials. Therefore, further research is required to discern alternative mechanisms that may also play an important role in Dox-induced toxicity. Thus, we aimed to investigate the role of mitochondrial fusion and fission in Dox-induced hepatic toxicity, which has not yet been investigated. Six-week-old male F344 rats were injected IP with 20mg/kg of Dox or saline. Once administered, both groups of animals were fasted with no food or water until sacrifice 24h later. Dox decreased content of primary regulators of mitochondrial fusion (OPA1, MFN1, and MFN2) with no effect on regulators of fission (DRP1 and FIS1), thus shifting the balance favoring mitochondrial fission. Moreover, it was determined that mitochondrial fission was likely not coupled to cell proliferation or cytochrome c release leading to the activation of mitochondrial-mediated apoptotic signaling. Rather, mitochondrial fission may be coupled to mitophagy and may be an adaptive response to protect against Dox-induced hepatic toxicity. This is the first study to report the role of altered mitochondrial dynamics and mitophagy machinery in Dox-induced hepatic injury.

关键词： ANIMAL dispersal   LANDSCAPES   ANIMAL species   ZOOGEOGRAPHY   ANIMAL populations   EMIGRATION & immigration  

摘要： Understanding and predicting the dynamics of range expansion is a major topic in ecology both for invasive species extending their ranges into non-native regions and for species shifting their natural distributions as a consequence of climate change. In an increasingly modified landscape, a key question is 'how do populations spread across patchy landscapes?' Dispersal is a central process in range expansion and while there is a considerable theory on how the shape of a dispersal kernel influences the rate of spread, we know much less about the relationships between emigration, movement and settlement rules, and invasion rates. Here, we use a simple, single species individual-based model that explicitly simulates animal dispersal to establish how density-dependent emigration and settlement rules interact with landscape characteristics to determine spread rates. We show that depending on the dispersal behaviour and on the risk of mortality in the matrix, increasing the number of patches does not necessarily maximise the spread rate. This is due to two effects: first, individuals dispersing at the expanding front are likely to exhibit lower net-displacement as they typically do not travel far before finding a patch;secondly, with increasing availability of high quality habitat, density-dependence in emigration and settlement can decrease the number of emigrants and their net-displacement. The rate of spread is ultimately determined by the balance between net travelled distance, the dispersal mortality and the number of dispersing individuals, which in turn depend on the interaction between the landscape and the species' dispersal behaviour. These results highlight that predicting spread rates in heterogeneous landscapes is a complex task and requires better understanding of the rules that individuals use in emigration, transfer and settlement decisions.

关键词： Copper interconnect   Elastic properties   PPP3R1 gene   Mechanical properties   Bundles   Carbon Nanotubes   GTF2E1 gene   Iron   elastic parameters   Finite   Molecular Dynamics  

摘要： As an important type of potential interconnection nanostructures, metallic carbon nanotube bundles (CNBs) are expected to replace the copper interconnect lines as interconnects in the microelectronic packaging. By embedding discontinuous CNBs in a soft matrix for considering the intertube Van der Waals interaction, a finite element (FE) model is proposed to estimate the effective mechanical properties of CNBs. We also propose a molecular dynamics (MD) model to predict the intertube spacing and elastic parameters of both the carbon nanotubes and soft matrix by combining the analytical equations. The present FE numerical results show a good agreement with the analytical andMD results. Compared to the micromechanics-based analytical model, the proposed FE model can give a more exact description for the CNBs with a finite size while offering tremendous improvements in computational cost. The influences of the number of the tubes, the radius of the individual tube, and the length of the CNBs on the effective elastic properties, are especially examined. It is found that the geometric factors play an important role in characterizing the effective elastic properties.

关键词： ARSENIC   AB initio methods (Quantum mechanics)   HYDROLYSIS   PROTON transfer reactions   HYDROGEN bonding   FOURIER transform infrared spectroscopy   OXONIUM ions  

摘要： This work presents a hybrid ab initio quantum mechanical/molecular mechanical simulation at the RI-MP2 level of theory investigating the hydrolysis process of arsenic(III), ultimately leading to arsenous acid (H3AsO3). A newly implemented dissociative water model has been applied to treat the interactions in the classical region, which is capable of describing non-neutral water species such as hydroxide and oxonium ions. Three stages of hydrolysis have been observed during the simulation and besides profound dynamical considerations, detailed insights into structural changes and atomic partial charge shifts are presented. In particular, the geometrical properties of H-bonds involved in each of the three proton transfer events and subsequent proton hopping reactions are discussed. A Laguerre tessellation analysis has been employed to estimate the molecular volume of H3AsO3. Estimations of pKa values of the arsenic(III)-aquo-complexes have been obtained at the G4 and CBS-Q//B3 levels of theory using a thermodynamic cycle, whereas rate constants for the final hydrolysis step have been determined via reaction path optimization and transition state theory. Newly recorded Fourier transform infrared (FT-IR) spectroscopy measurements have been compared to power spectra obtained from the simulation data, confirming its quality. The simulation findings, as well as results from computational spectroscopic calculations utilizing the PT2-VSCF methodology, proved valuable for the interpretation of the experimental FT-IR data, elucidating the particularities of the strongly observed IR Raman noncoincidence effect.

关键词： net Cd influx   root absorbing power   soil solution concentration   model   sensitivity analysis  

摘要： Maize, sunflower, flax, and spinach differed in the accumulation of Cd when grown on a Cd contaminated soil. This was mainly due to the different Cd net influx, I-n , that varied among species by a factor of up to 30. The objective of this study was to find possible reasons for the different Cd I-n by using a mechanistic model. After 14days of Cd uptake the model calculated only a small Cd depletion at the root surface, e.g. from 0.22mol L(-1)down to 0.19mol L(-1)for maize and from 0.48mol L(-1)down to 0.35mol L(-1)for spinach. Even so the model always overestimated the Cd I-n , for spinach by a factor of 1.5 and for maize by a factor of 10. Only simulating a decrease of C-Li or the root absorbing power, , by 40% to 90% gave an agreement of calculated and measured I-n . This may be interpreted as that about 40% in the case of spinach and 90% in the case of maize of the Cd in soil solution were not accessible for plant uptake. The high sensitivity to also shows that not the Cd transport to the root but was limiting the step for Cd uptake.