A Class of Vector Lyapunov Functions for Stability Analysis of Nonlinear Impulsive Differential Systems

A novel and effective approach to stability of the solutions of nonlinear systems with impulsive effect is considered. The investigations are carried out by means of a class of vector Lyapunov functions and differential inequalities for piecewise continuous functions. Simulation examples are given to illustrate the presented results

Development of a post-form strength prediction model for a 6xxx aluminium alloy in a novel forming process

Accurate prediction of the post-form strength of structural components made from 6xxx series aluminium alloys has been a challenge, especially when the alloy undergoes complex thermo-mechanical processes such as the Fast light Alloys Stamping Technology (FAST). This process involves ultra-fast heating, high temperature plastic deformation, rapid quenching and is followed by multi-stage artificial ageing heat treatment. The strength of the material evolves with the formation of second phase precipitates during the entire process. The widely accepted precipitation sequence is SSSS - clusters - β” - β’ - β. However, due to the complexity of deformations and thermal profile during the process, the classic theory is not applicable. Therefore, in this research, precipitation behaviour during ultra-fast heating, viscoplastic behaviour, effect of residual dislocations generated during high temperature deformation, quenching sensitivity and multi-stage artificial ageing response have been comprehensively studied. A set of experiments, including ultra-fast heating tests, uniaxial tensile tests, pre-straining uniaxial tensile tests, quenching tests, artificial ageing tests and TEM observations were conducted to provide a thorough understanding of the novel forming technology. The underlying mechanisms for the FAST process were investigated through the in-depth analysis of experimental results. ·Under ultra-fast heating conditions, most of the precipitates are dissolved and the spherical pre-β” precipitates are formed and finely dispersed in the aluminium matrix, which are beneficial to accelerate the subsequent precipitation process. ·The residual dislocations, generated during plastic deformation, strengthen the material and act as nucleation sites for precipitates. The peak strength is reduced owing to the uneven accumulation of precipitates around dislocations. ·The coarse β’ and β precipitates induced due to the insufficient quenching are detrimental to precipitation response. These quench-induced precipitates consume both solute atoms and vacancies, which are unable to be reversely transferred to the preferred needle-shaped β” precipitates. Based on the scientific achievements, a mechanism-based unified post-form strength (PFS) prediction model was developed ab-initio to predict the strength evolution of the material during the entire complex FAST process with highly efficient computation. Constitutive equations were proposed to model the viscoplastic behaviour at elevated temperature. Important microstructural parameters, including dislocation density, volume fraction, radius of precipitates and solute concentration were correlated to predict the material strength. The particle size distribution (PSD) sub-model was further established to accurately interpret the detailed microstructural changes during the complex thermo-mechanical processes. Furthermore, the model has been programmed into an advanced functional module ‘Tailor’ and implemented into a cloud based FEA platform. The predictive capability of the module was verified by conducting forming tests of a U-shaped component in a dedicated pilot production line. It was found that the ‘Tailor’ module was able to precisely predict the post-form strength in agreement with experiments, with a deviation of less than 7% compared to experimental results.Open Acces

The Effect of Initial State Error for Nonlinear Systems with Delay via Iterative Learning Control

An iterative learning control problem for nonlinear systems with delays is studied in detail in this paper. By introducing the λ-norm and being inspired by retarded Gronwall-like inequality, the novel sufficient conditions for robust convergence of the tracking error, whose initial states are not zero, with time delays are obtained. Finally, simulation example is given to illustrate the effectiveness of the proposed method

Chaotic Tolerant Synchronization Analysis with Propagation Delay and Actuator Faults

The criteria for tolerant synchronization with a constant propagation delay and actuator faults are presented by using matrix analysis techniques. A new algorithm, which constructs the extended error systems in order to make the conservation of the stability lower, is proposed. Based on proper Lyapunov-Krasovskii functional, the novel delay-dependent fault tolerant synchronization analyses are derived. Finally, numerical examples show the effectiveness of the proposed method

Empirical model for fitting the viscosity of lithium bromide solution with CuO nanoparticles and E414

To research viscosity fitting model of stable nano-lithium bromide solution (nano-LiBr), the stability of the nano-LiBr and the dynamic viscosity of LiBr were measued by Ultraviolet-visible spectroscopy (UV-vis) and rotational viscometer respectively. Two LiBr with different additives were measured, i.e., LiBr with dispersant (E414) and LiBr with dispersant + copper oxide nanoparticles (CuO). The ranges of measuring temperature were from 25°C–60°C, the concentrations of LiBr were from 50%–59%, the volume fractions of the dispersants were from 0%–4%, and the fractions of nanoparticle volume were from 0%–0.05%. Results indicated that the nano-LiBr with E414 had good stability. The viscosity of the LiBr decreased when temperature increased, and increased when LiBr concentration and dispersant amount were increased. It is also found that the viscosity was directly proportional to the volume fraction of the nanoparticles. This study also showed that the higher the concentration of the base fluid was, the more significant increase of the viscosity was. An empirical viscosity model of stable nano-LiBr with a maximum error of 13% was developed

Reactive Oxygen Species Affect the Tenderness of Bovine Muscle by Regulating Glycolysis during the Early Stage of Postmortem Cold Storage

This study was conducted to investigate the regulatory mechanism of reactive oxygen species (ROS) on the glycolysis pathway of bovine muscle and its impact on meat tenderness at the early stage of postmortem cold storage. Fresh beef was treated with hydrogen peroxide (H2O2) as a major ROS, N-acetyl-L-cysteine (NAC) as an ROS scavenger, or physiological saline as a control before being stored at 4 ℃. After 0.5, 6, 12, 24, and 48 hours, the glycolysis level and tenderness indices were assessed. In addition, tandem mass tag (TMT)-labeled quantitative proteomics was used for protein identification and quantitative analysis of the samples after 24 hours and for screening of differential proteins in the glycolysis pathway. The findings showed that the glycolysis level increased significantly in the H2O2-treated group, and glycogenolysis and lactic acid accumulation were significantly higher than those in the other two groups (P < 0.05). In contrast, the glycolysis process was significantly suppressed by NAC treatment. The H2O2-treated group reached the ultimate pH after 12 hours, 12 and 36 hours earlier than the control and NAC groups, respectively. The shear force of the H2O2-treated group reached its maximum after 12 hours, and the myofibrillar fragmentation index (MFI) was significantly greater than that of the other two groups after 6–48 hours (P < 0.05), indicating that a higher ROS level can accelerate the tenderization of bovine muscle by enhancing the glycolysis capacity during postmortem refrigeration. Totally eight up-regulated proteins and two down-regulated proteins in the glycolysis pathway were identified in the H2O2-treated versus control groups after 24 hours of refrigeration. Among these proteins, the up-regulated core proteins of phosphoglycerate mutase (PGAM), enolase (ENO), and pyruvate dehydrogenase E1 subunit beta (PDHB) coordinated with the down-regulated pyruvate dehydrogenase E1 subunit alpha (PDHA) to accelerate the glycolysis process. In conclusion, ROS can speed up glycolysis and consequently improve meat tenderness by regulating the expression of key proteins in the glycolysis pathway

Ammonia Affects Mitochondrial Cell Apoptosis and Tenderness in Postmortem Yak Meat by Regulating Hypoxia Inducible Factor-1α Expression

This study aimed to investigate the effect of ammonia mediated hypoxia inducible factor-1α (HIF-1α) expression on mitochondrial cell apoptosis and tenderness in yak meat after slaughter. Ten mmol/L ammonium chloride (NH4Cl), 0.9% normal saline (control) and 10 mmol/L N-nitro-L-arginine methyl ester hydrochloride were used separately for treating yak Longissimus dorsi. By measuring the expression of HIF-1α, nitrogen monoxide (NO) content, energy metabolism-related enzyme activities, adenosine triphosphate (ATP) level, mitochondrial pathway of apoptosis and muscle tenderness, we explored the mechanism of cell apoptosis and tenderness change in yak meat after slaughter. The results showed that during the postmortem aging of yak meat, the expression of HIF-1α and the content of NO in each treatment group increased first and then decreased, and so did the activities of Na+-K+-ATPase, Ca2+-ATPase, caspase-9 and caspase-3 and shear stress. ATP content, the degree of mitochondrial permeability transition pore (MPTP) opening, mitochondrial membrane potential (MMP), and muscle fiber diameter and area showed a gradual downward trend, and myofibril fragmentation index (MFI) and the gap between muscle cells showed an opposite trend. During 6 to 24 h after slaughter, the expression of HIF-1α and the content of NO in the NH4Cl treatment group were significantly higher than those in the control group (P < 0.05), which were significantly higher than those in the L-NAME treatment group (P < 0.05). The ATP content in the NH4Cl group was significantly higher than that in the control and L-NAME groups during 6 to 72 h after slaughter. The activities of Na+-K+-ATPase and Ca2+-ATPase in the control group were significantly higher than those in the NH4Cl group (P < 0.05), but significantly lower than those in the L-NAME group (P < 0.05). During 6–120 h after slaughter, the opening of MPTP in the control group was significantly higher than that in the NH4Cl group (P < 0.05), but lower than that in the L-NAME group (P < 0.05). During 0 to 168 h after slaughter, the opening of MMP decreased by 47.72% in the NH4Cl group, 53.54% in the control group, and 60.05% in the L-NAME group. During 6 to 72 h after slaughter, the activities of caspase-9 and caspase-3 in the NH4Cl group were significantly lower than those in the control group (P < 0.05), which were lower than those in the L-NAME group (P < 0.05). During 6 to 120 h after slaughter, shear force and muscle fiber area and diameter in the NH4Cl group were higher than those in the control group, and MFI and the gap between muscle fibers in the NH4Cl group were lower than those in the control group, while the opposite result was observed for the L-NAME group. In conclusion, ammonia decreased the activities of Na+-K+-ATPase and Ca2+-ATPase and increased the content of ATP by up-regulating the expression of HIF-1α, which in turn regulated the energy metabolism of muscle cells and maintained the stability of the internal environment. By inhibiting the opening of MPTP and the decrease in MMP, ammonia reduced the activity of caspase-3/9, and inhibited mitochondrial cell apoptosis, thereby resulting in an increase in shear stress, a decrease in MFI and morphological changes of muscle cells, and finally causing a negative effect on the tenderness of yak meat

Electrically Guiding Migration of Human Induced Pluripotent Stem Cells

A major road-block in stem cell therapy is the poor homing and integration of transplanted stem cells with the targeted host tissue. Human induced pluripotent stem (hiPS) cells are considered an excellent alternative to embryonic stem (ES) cells and we tested the feasibility of using small, physiological electric fields (EFs) to guide hiPS cells to their target. Applied EFs stimulated and guided migration of cultured hiPS cells toward the anode, with a stimulation threshold of <30 mV/mm; in three-dimensional (3D) culture hiPS cells remained stationary, whereas in an applied EF they migrated directionally. This is of significance as the therapeutic use of hiPS cells occurs in a 3D environment. EF exposure did not alter expression of the pluripotency markers SSEA-4 and Oct-4 in hiPS cells. We compared EF-directed migration (galvanotaxis) of hiPS cells and hES cells and found that hiPS cells showed greater sensitivity and directedness than those of hES cells in an EF, while hES cells migrated toward cathode. Rho-kinase (ROCK) inhibition, a method to aid expansion and survival of stem cells, significantly increased the motility, but reduced directionality of iPS cells in an EF by 70–80%. Thus, our study has revealed that physiological EF is an effective guidance cue for the migration of hiPS cells in either 2D or 3D environments and that will occur in a ROCK-dependent manner. Our current finding may lead to techniques for applying EFs in vivo to guide migration of transplanted stem cells