Adaptive Neural Back-Stepping Control with Constrains for a Flexible Air-Breathing Hypersonic Vehicle

The design of an adaptive neural back-stepping control for a flexible air-breathing hypersonic vehicle (AHV) in the presence of input constraint and aerodynamic uncertainty is discussed. Based on functional decomposition, the dynamics can be decomposed into the velocity subsystem and the altitude subsystem. To guarantee the exploited controller’s robustness with respect to parametric uncertainties, neural network (NN) is applied to approximate the lumped uncertainty of each subsystem of AHV model. The exceptional contribution is that novel auxiliary systems are introduced to compensate both the tracking errors and desired control laws, based on which the explored controller can still provide effective tracking of velocity and altitude commands when the actuators are saturated. Finally, simulation studies are made to illustrate the effectiveness of the proposed control approach in spite of the flexible effects, system uncertainties, and varying disturbances

Hyperbranched Liquid Crystals Modified with Sisal Cellulose Fibers for Reinforcement of Epoxy Composites

Well-defined functionalized sisal cellulose fibers (SCFs) grafted on hyperbranched liquid crystals (HLP) were synthesized to improve the compatibility between SCFs and epoxy resin (EP). The influence of SCFs-HLP on the mechanical and thermal properties of SCFs-HLP/EP composites was studied. The results show that the mechanical properties of SCFs-HLP/EP composites were enhanced distinctly. Particularly, compared with EP, impact strength, tensile strength, and flexural strength of composites with 4.0 wt % SCFs-HLP were 38.3 KJ·m−2, 86.2 MPa, and 150.7 MPa, increasing by 118.7%, 55.6%, and 89.6%, respectively. As well, the glass transition temperature of the composite material increased by 25 °C. It is hope that this work will inform ongoing efforts to exploit more efficient methods to overcome the poor natural fiber/polymer adhesion in the interface region

Enhanced mechanical and thermal properties of polypropylene/cellulose fibers composites with modified tannic as a compatibilizer

A novel compatibilizer tannic grafted poly(12-hydroxy stearate) (TA-g-PHS) was synthesized using tannic and 12-hydroxystearic acid as raw materials through the esterification reaction. The compatibilizer was used to improve the compatibility between polypropylene (PP) and microcrystalline cellulose fibers (MCF). The impact strength and tensile strength of MCF/PP composites modified with the TA-g-PHS were 38.51 kJ/m(2) and 30.45 MPa when the content loading of TA-g-PHS is 3 wt% and MCF is 10 wt%, which were improved by 40.5% and 76.9%, respectively, compared to the MCF/PP composites alone. The melt flow rate improved with the addition of TA-g-PHS. And the thermal properties have slightly improved. Moreover, the SEM images of the fracture surfaces display that MCF is relatively well dispersed in the PP matrix by adding TA-g-PHS. It can be inferred that the PP and MCF matrix interfacial bonding was strengthened. POLYM. COMPOS., 39:2036-2045, 2018. (c) 2016 Society of Plastics Engineer

Enhanced mechanical and thermal properties of polypropylene/cellulose fibers composites with modified tannic as a compatibilizer

A novel compatibilizer tannic grafted poly(12-hydroxy stearate) (TA-g-PHS) was synthesized using tannic and 12-hydroxystearic acid as raw materials through the esterification reaction. The compatibilizer was used to improve the compatibility between polypropylene (PP) and microcrystalline cellulose fibers (MCF). The impact strength and tensile strength of MCF/PP composites modified with the TA-g-PHS were 38.51 kJ/m(2) and 30.45 MPa when the content loading of TA-g-PHS is 3 wt% and MCF is 10 wt%, which were improved by 40.5% and 76.9%, respectively, compared to the MCF/PP composites alone. The melt flow rate improved with the addition of TA-g-PHS. And the thermal properties have slightly improved. Moreover, the SEM images of the fracture surfaces display that MCF is relatively well dispersed in the PP matrix by adding TA-g-PHS. It can be inferred that the PP and MCF matrix interfacial bonding was strengthened. POLYM. COMPOS., 39:2036-2045, 2018. (c) 2016 Society of Plastics Engineer

Effect of epoxidized soybean oil grafted poly(12-hydroxy stearate) on mechanical and thermal properties of microcrystalline cellulose fibers/polypropylene composites

A new green compatibilizer named epoxidized soybean oil grafted poly(12-hydroxy stearate) (ESO-g-PHS) was successfully synthesized using 12-hydroxy stearic acid and epoxidized soybean oil (ESO). The chemical structure of ESO-g-PHS was investigated through Fourier transformed infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. ESO-g-PHS was used as a compatibilizer to enhance the interfacial compatibility between polypropylene (PP) and microcrystalline cellulose fibers (MCF). The results showed that the impact strength and tensile strength were 33.55 and 27.57 MPa when the content loading of MCF reached 10 wt% and ESO-g-PHS was 4 wt%, which enhanced by 75.4 and 30.04 %, respectively, compared to that of composites without ESO-g-PHS. In addition, the SEM images of the fracture surfaces display that PP was highly bonded to MCF with ESO-g-PHS treated. In addition, the wide angle X-ray diffraction measurement revealed that the addition of ESO-g-PHS did not change the crystal structure of PP. Moreover, there was a slight improvement in thermal properties for PP composites with the addition of ESO-g-PHS

Intramolecular dynamic coupling slows surface relaxation of polymer glasses

Abstract Over the past three decades, studies have indicated a mobile surface layer with steep gradients on glass surfaces. Among various glasses, polymers are unique because intramolecular interactions — combined with chain connectivity — can alter surface dynamics, but their fundamental role has remained elusive. By devising polymer surfaces occupied by chain loops of various penetration depths, combined with surface dissipation experiments and Monte Carlo simulations, we demonstrate that the intramolecular dynamic coupling along surface chains causes the sluggish bulk polymers to suppress the fast surface dynamics. Such effect leads to that accelerated segmental relaxation on polymer glass surfaces markedly slows when the surface polymers extend chain loops deeper into the film interior. The surface mobility suppression due to the intramolecular coupling reduces the magnitude of the reduction in glass transition temperature commonly observed in thin films, enabling new opportunities for tailoring polymer properties at interfaces and under confinement and producing glasses with enhanced thermal stability

Improving thermal and mechanical properties of epoxy composites by using functionalized graphene

Perylene tetracarboxylic anhydride (PTCDA) was reacted with 6-aminocaproic acid to form the corresponding perylene bisimide (PBI). PBI was used as the foundation for oligomerisation of glycidol in a ring-opening reaction of glycidol leading to a hyper branched, water-soluble glycidol derivative of perylene (PBI-HPG). PBI-HPG was bound to the reduced graphene oxide via pi-pi stacking resulting in a compound termed PBI-HPG/RGO. The structure and morphology of PBI-HPG/RGO were investigated by infrared spectroscopy (FT-IR), wide angle X-ray diffractometry (WAXD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). PBI-HPG/RGO was blended at different loadings in order to improve the thermal and mechanical properties of epoxy composites. The maximum T-g of the epoxy composites was about 20 degrees C and the decomposition temperature (T-d) was 26 degrees C higher than that of neat epoxy. The incorporation of PBI-HPG/RGO yields a material with an impact strength of 39.6 kJ m(-2) and a tensile strength at 0.7 wt%. It increased by 50.8% and 62.3%, respectively, compared to the neat epoxy

γ-glutamylcysteine exhibits anti-inflammatory effects by increasing cellular glutathione level

Sepsis is a life-threatening organ dysfunction caused by dysregulated host response to infection and characterized by redox imbalance and severe oxidative stress. Glutathione (GSH) serves several vital functions, including scavenging free radicals and maintaining intracellular redox balance. Extracellular GSH is unable to be taken into the majority of human cells, and the GSH prodrug N-acetyl-l-cysteine (NAC) does not exhibit promising clinical effects. γ-glutamylcysteine (γ-GC), an intermediate dipeptide of the GSH-synthesis pathway and harboring anti-inflammatory properties, represents a relatively unexplored option for sepsis treatment. The anti-inflammatory efficiency of γ-GC and the associated molecular mechanism need to be explored. In vivo investigation showed that γ-GC reduced sepsis lethality and attenuated systemic inflammatory responses in mice, as well as inhibited lipopolysaccharide (LPS)-stimulated production of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), high-mobility group box 1 (HMGB1), and nitric oxide (NO) and the expression of inducible NO synthase and cyclooxygenase 2 in RAW264.7 cells. Moreover, both in vivo and in vitro experiments demonstrated that γ-GC exhibited better therapeutic effects against inflammation compared with N-acetyl-L-cysteine (NAC) and GSH. Mechanistically, γ-GC suppressed LPS-induced reactive oxygen species accumulation and GSH depletion. Inflammatory stimuli, such as LPS treatment, upregulated the expression of glutathione synthetase via activating nuclear factor-erythroid 2-related factor (Nrf2) and nuclear factor kappa B (NF-κB) pathways, thereby promoting synthesis of GSH from γ-GC. These findings suggested that γ-GC might represent a potential therapeutic agent for sepsis treatment. Keywords: γ-glutamylcysteine, Sepsis, Glutathione, N-acetyl-L-cysteine, Glutathione synthetas