Search

Many emerging materials, such as ultrastable glasses.sup.1,2 of interest for phone displays and OLED television screens, owe their properties to a gradient of enhanced mobility at the surface of glass-forming liquids. The discovery of this surface mobility enhancement.sup.3-5 has reshaped our understanding of the behaviour of glass formers and of how to fashion them into improved materials. In polymeric glasses, these interfacial modifications are complicated by the existence of a second length scale--the size of the polymer chain--as well as the length scale of the interfacial mobility gradient.sup.6-9. Here we present simulations, theory and time-resolved surface nano-creep experiments to reveal that this two-scale nature of glassy polymer surfaces drives the emergence of a transient rubbery, entangled-like surface behaviour even in polymers comprised of short, subentangled chains. We find that this effect emerges from superposed gradients in segmental dynamics and chain conformational statistics. The lifetime of this rubbery behaviour, which will have broad implications in constraining surface relaxations central to applications including tribology, adhesion, and surface healing of polymeric glasses, extends as the material is cooled. The surface layers suffer a general breakdown in time-temperature superposition (TTS), a fundamental tenet of polymer physics and rheology. This finding may require a reevaluation of strategies for the prediction of long-time properties in polymeric glasses with high interfacial areas. We expect that this interfacial transient elastomer effect and TTS breakdown should normally occur in macromolecular systems ranging from nanocomposites to thin films, where interfaces dominate material properties.sup.5,10. Surface enhancements in glass mobility are complicated in polymers by the interplay of the surface mobile layer thickness with a second length scale (the size of the polymer chains), giving rise to a transient rubbery surface even in polymers with short chains., Author(s): Zhiwei Hao [sup.1] , Asieh Ghanekarade [sup.2] , Ningtao Zhu [sup.1] , Katelyn Randazzo [sup.3] , Daisuke Kawaguchi [sup.5] , Keiji Tanaka [sup.5] , Xinping Wang [sup.1] , David [...]

In this paper, we study the real interpolation theory for variable Lorentz–Karamata spaces as well as for the corresponding martingale Hardy spaces. As a consequence, the generalization of Doob's maximal inequality will be proved. Moreover, the atomic decompositions of the variable martingale Hardy–Lorentz–Karamata spaces are also presented. The results obtained here are new even for martingale Hardy–Lorentz–Karamata spaces. [ABSTRACT FROM AUTHOR]

Self‐resistance electric (SRE) heating for the curing of carbon fiber reinforced plastic (CFRP) offers the benefits of saving energy consumption and reducing investment in equipment. In this work, the investigation was carried out to illustrate the effect of carbon nanotubes (CNTs) addition (0.5, 1.0, and 1.5 wt%) on the thermoset curing and mechanical properties of carbon fiber‐reinforced epoxy laminates fabricated by SRE heating method. The results show that adding CNTs can improve the temperature uniformity and interlayer‐resin flow during the SRE heating process and have a limited influence on the curing degree of CFRP composites. The tensile strength in the longitudinal direction of the composites increased with the increase of CNT addition. Meanwhile, the flexural strength and interlaminar shear strength had the maximum value with the CNTs content of 0.5 wt% and decreased significantly at the CNTs content of 1.5 wt%. It concludes that the appropriate content of CNTs addition has the potential to improve the thermoset curing performance and mechanical properties of the CFRP laminate composites fabricated by SRE heating. Highlights: This study focuses on the effect of CNT addition on SRE heating for CFRP.The addition of CNTs improved the temperature uniformity during SRE heating.The addition of CNTs can reduce the voids of SRE‐cured CFRP composites.Threshold value of CNTs affected the mechanical performance of SRE‐cured CFRP. [ABSTRACT FROM AUTHOR]

A novel estimation scheme for joint torque information is constructed by observer design method in the case that force/torque/velocity/acceleration sensors of manipulator are not available. Based on generalized dynamic scaling function and scalar filtering, the globally exponentially stable observer for torque estimation with only position measurement is presented in this article. The main contribution lies in the development of the classic Nicosia observer with performance improvements and significant order reduction compared to the existing results. Comparative simulations demonstrate the effectiveness and superiority of the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a novel neural-network-based (NN-based) adaptive composite terminal sliding mode (TSM) control scheme for a class of spacecraft systems with mismatched disturbances and input uncertainties. The key point of the proposed scheme is that the multiple uncertainties are considered and well-handled by the combined second-order disturbance observer (SODO) method and an NN. First, for the purpose of handling the mismatched disturbances, a SODO is applied to obtain the exact estimation of the mismatched disturbances. Second, for satisfying the output constraints and avoiding the computational complexity, the constrained output signals are transformed into unconstrained ones by error transformation. Moreover, to ensure the fast convergence characteristic of the considered system, a SODO-based composite nonsingular terminal sliding mode (SODO-NTSM) manifold is designed. Furthermore, the external disturbances, the input uncertainties, and the unknown nonlinearities are considered by several adaptive laws. As a result, by combining the SODO-NTSM manifold, the external disturbances adaptive compensation laws, the adaptive compensation laws of the input uncertainties, and the NN weights adaptive update laws, the novel new NN-based adaptive composite TSM control scheme is established for the spacecraft system. The simulation results show that the proposed scheme presents the satisfactory control performance. [ABSTRACT FROM AUTHOR]

This paper proposed an observer-based output feedback tracking controller with output constraints for the rigid-link flexible-joint space manipulator system considering the dynamic damping caused by the torque change. By combining the Barrier Lyapunov function, backstepping, coordinate transformation, dynamic scaling, and globally exponentially convergent velocity observer, the proposed scheme maintains the simplicity of independent design of observer and controller, where the observation gains and control gains can be designed separately. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites are a class of composite materials containing polymer continuous phase as matrix and inorganic nanoparticles as fillers. Combining the advantages of both polymer and nanofillers, polymer nanocomposites can yield some desirable functionalities that cannot be achieved by the individual components, thus exhibiting tremendous potential for a variety of applications. However, their performances markedly depend on the dispersion and distribution of nanofillers in the polymer matrix. Recently, in situ emulsion polymerization has been demonstrated to be a powerful approach for the preparation of multifunctional polymer nanocomposites with good dispersion and homogeneous distribution of nanofillers. In this review, the fundamentals of polymer nanocomposites and their preparation strategies are briefly discussed, and then are comprehensively summarized recent advances in the design, preparation, functionalization, and applications of polymer nanocomposites via in situ emulsion polymerization. The particular focus is placed on the strategies for achieving homogeneous and good dispersion of nanofillers within polymer matrixes. Moreover, the current challenges and future opportunities of in situ emulsion polymerization to polymer nanocomposites are discussed to motivate future contributions and explore new possibilities. [ABSTRACT FROM AUTHOR]

Oil and gas resources are closely related to daily life and are an important support for the economy of a city or even a country. Hydraulic fracturing is an indispensable technique to economically develop oil and gas resources through creating complex fractures. Temporary plugging and diverting fracturing (TPDF) can generate diversion fractures perpendicular to the initial fractures and enhance the stimulated area. The aperture of the diversion fractures determines its conductivity and the oil/gas production. However, it is difficult to evaluate the aperture of the diversion fracture due to the complex physical process of hydraulic fracturing. This work established a fluid–solid fully coupled simulation model to investigate the fracture aperture influenced by various factors during TPDF. The model can simulate the propagation of the initial fracture and the diversion fracture. Various factors include the tight plug's permeability, the tight plug's length, Young's modulus, rock tensile strength, in situ stress contrast, the leak-off coefficient of the fracture surface, and fluid injection rate. The results show that the aperture of the previous fracture can be enlarged, and the aperture of the diversion fracture can be decreased by the tight plug. The aperture at the diversion fracture mouth is much smaller than that along the diversion fracture. Reservoirs with low Young's modulus values and high rock tensile strength can generate the diversion fracture with a wider aperture. Moreover, increasing the fluid injection rate can effectively increase the fracture mouth aperture. In this way, the risk of screenout can be lowered. This work is beneficial for the design of the TPDF and ensures safe construction. [ABSTRACT FROM AUTHOR]

Diallyl sulfide (DAS), as a major component of garlic extracts, has been shown to inhibit growth of hepatocellular carcinoma cells (HCC), but the underlying mechanism is still elusive. In this study, we aimed to explore the involvement of autophagy in DAS‐induced growth inhibition of HepG2 and Huh7 hepatocellular carcinoma cells. We studied growth of DAS‐treated HepG2 and Huh7 cells using the MTS and clonogenic assays. Autophagic flux was examined by immunofluorescence and confocal microscopy. The expression levels of autophagy‐related proteins AMPK, mTOR, p62, LC3‐II, LAMP1, and cathepsin D in the HepG2 and Huh7 cells treated with DAS as well as the tumors formed by HepG2 cells in the nude mice in the presence or absence of DAS were examined using western blotting and immunohistochemistry analysis. We found that DAS treatment induced activation of AMPK/mTOR, and accumulation of LC3‐II and p62 both in vivo and in vitro. DAS inhibited autophagic flux through blocking the fusion of autophagosomes with lysosomes. Furthermore, DAS induced an increase in lysosomal pH and inhibition of Cathepsin D maturation. Co‐treatment with an autophagy inhibitor (Chloroquine, CQ) further enhanced the growth inhibitory activity of DAS in HCC cells. Thus, our findings indicate that autophagy is involved in DAS‐mediated growth inhibition of HCC cells both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Hybrid latex particles combine the unique properties of inorganic nano/micro particles with the inherent properties of polymers, exhibiting tremendous potential for a variety of applications. Recent years have witnessed an increased interest in the design and preparation of hybrid latex particles with well-defined size, structure and morphology. Due to its simplicity, versatility and environmental friendliness, the in situ (Pickering) emulsion polymerization has been demonstrated to be a powerful approach for the large-scale preparation of hybrid latex particles. In this review, the strategies and applications of in situ (Pickering) emulsion polymerization for the preparation of hybrid latex particles are systematically summarized. A particular focus is placed on the strategies for the preparation of hybrid latex particles with enhanced properties and well-defined core–shell, yolk–shell, multinuclear, raspberry-like, dumbbell-shaped, multipod-like or armored morphologies. We hope that the considerable advances, examples and principles presented in this review can motivate future contributions to provide a deeper understanding of current preparation technologies, develop new processes, and enable further exploitation of hybrid latex particles with outstanding characteristics and properties. [ABSTRACT FROM AUTHOR]

An output feedback trajectory tracking control scheme for nonholonomic mobile manipulator robot systems with full-output constraints is presented in this article. Different from the previous methods, the kinematic model of the system is transformed into a special chained form by a rotation-like matrix. A globally exponentially stable speed observer with generalized dynamic scaling function is constructed to obtain the velocity estimation of the system. The output feedback tracking constrained controller is successfully constructed by Barrier Lyapunov function, backstepping and the excellent observer, which considering the system dynamics and the full-output constraints is achieved with only measurable outputs. [ABSTRACT FROM AUTHOR]

In this paper, we deal with the existence and multiplicity of solutions for fractional p (x) -Kirchhoff-type problems as follows: { M (∫ Q 1 p (x , y) | v (x) − v (y) | p (x , y) | x − y | d + s p (x , y) d x d y) (− Δ p (x) ) s v (x) = λ | v (x) | r (x) − 2 v (x) , in Ω , v = 0 , in R d ∖ Ω , where (− △ p (x) ) s is the fractional p (x) -Laplacian. Different from the previous ones which have recently appeared, we weaken the condition of M and obtain the existence and multiplicity of solutions via the symmetric mountain pass theorem and the theory of the fractional Sobolev space with variable exponents. [ABSTRACT FROM AUTHOR]