Summary
This paper considers the problem of state feedback finite‐time stabilization for a class of high‐order nonlinear systems with an output constraint. By proposing a novel tan‐type barrier ...Lyapunov function combined with manipulating sign functions, the technique of adding a power integrator is skillfully revamped to develop a systematic approach that guides us to construct a state feedback finite‐time stabilizer for high‐order nonlinear systems while preventing the violation of a prespecified output constraint during operation. The proposed approach is a unified tool in the sense that it can provide a finite‐time stabilizer design even when the constraint is infinite, or equivalently, there is no need for a constraint. A simple example is presented to demonstrate the effectiveness of the proposed strategy.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Polyacrylonitrile (PAN) is a versatile man-made polymer and has been used in a large array of products since its first mass production in the mid 40s. Among all applications of PAN the widely used ...application is in manufacture of precursor fiber for fabrication of carbon fibers. The process of PAN-based carbon fiber production comprises fiber spinning, thermal stabilization and carbonization stages. Carbon fiber properties are significantly dependent on the quality of PAN precursor fiber and in particular the process parameters involved in thermal stabilization. This paper is the first comprehensive review that provides a general understanding of the links between PAN fiber structure, properties, and its stabilization process along with the use of mathematical modelling as a powerful tool in prediction and optimization of the processes involved. Since the promise of the mathematical modelling is to predict the future behaviour of the system and the value of the variables for the unseen or unmeasured domain of variables; and in the era of industry 4.0 rise, this review will be valuable in further understanding of the intricate processes of carbon fiber manufacture and utilising the advanced mathematical modelling using machine learning techniques to predict and optimize a range of critical factors that control the quality of PAN and resultant carbon fibers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Traditional macroeconomic stabilization policies seek to moderate swings in economic activity through measures that primarily augment aggregate demand. Such measures are, however, inadequate in ...mitigating the comprehensive effects of crisis such as the COVID-19, which affects both the demand and supply sides of the economy. Moreover, monetary policies are presently close to a liquidity trap combined with weakened transmission links to the real economy. Fiscal policies have been reactivated, albeit in an ad hoc and experimental manner. Based on a literature review and the policy responses following the COVID-19 crisis, the objective is to present a modified and extended framework for stabilization policies. In particular, the importance of microeconomic supply-side measures that promote entrepreneurial processes and knowledge-upgrading efforts are emphasized. Furthermore, a coherent realigning of policies at the micro- and macro-levels is argued to enhance the potential for long-term growth and to facilitate the restructuring of an economy that normally follows a crisis.
Plain English Summary
The COVID-19 crisis makes traditional stabilization policies obsolete. Reinstate the market and redirect policy from interest rates and unconditional state support toward providing employees and firms with adequate knowledge for future challenges. Traditional crises policies seek to moderate swings in economic activity by primarily lowering interest rates and increase governmental expenditure to stimulate demand and economic activity. However, the effectiveness of both of these measures has been questioned, in particular, further reductions in already extremely low-interest rates. The present COVID-19 crisis has highlighted the importance of taking firms, entrepreneurs, trade, etc., into account, i.e., the supply side of the economy. It is argued that traditional policies should partly be replaced by measures targeting entrepreneurial processes, firm growth, innovation, and knowledge upgrading. Corporate taxes should be used to increase firms’ crisis resilience, increase investment, and encourage start-ups, while state support should be conditioned on employees engaging in knowledge upgrading. Hence, the main conclusion of this study is that such redirection of policies will more effectively level out swings in the business cycle, increase the potential for long-term growth, and make it easier for employees and firms to adjust to new economic conditions.
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CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We solve the prescribed-time mean-square stabilization and inverse optimality control problems for stochastic strict-feedback nonlinear systems by developing a new nonscaling backstepping design ...scheme. A key novel design ingredient is that the time-varying function is not used to scale the coordinate transformations and is only suitably introduced into the virtual controllers. The advantage of this approach is that a simpler controller results and the control effort is reduced. By using this method, we design a new controller to guarantee that the equilibrium at the origin of the closed-loop system is prescribed-time mean-square stable. Then, we redesign the controller and solve the prescribed-time inverse optimal mean-square stabilization problem, with an infinite gain margin. Specifically, the designed controller is not only optimal with respect to a meaningful cost functional but also globally stabilizes the closed-loop system in the prescribed-time. Finally, two simulation examples are given to illustrate the stochastic nonlinear prescribed-time control design.
This paper considers the problem of sampled-data adaptive output feedback fuzzy stabilization for switched uncertain nonlinear systems associated with asynchronous switching. A state observer is ...designed to estimate the unmeasured states and fuzzy logic systems are employed to deal with the unknown nonlinear terms. Sampled-data controller and novel switched adaptive laws are constructed based on the recursive design method and an average dwell time constraint is given to ensure that the closed-loop system is stable. The proposed scheme is employed in a mass-spring-damper system to demonstrate its effectiveness.
•Humic acid residue (HAS) is currently a wasted resource.•We modified HAS with NH4H2PO4 to improve its heavy metal stabilization capacity.•N-HAS reduces the mobility of Hg and Pb in soils.•Addition ...of N-HAS alters soil physicochemical properties.•N-HAS was an industrially produced heavy metal passivator.
Humic acid residue (HAS), as a waste product from the extraction of humic acid from low-rank coal such as weathered coal and lignite, is characterized by its abundant yield and low price. However, the low efficiency and high pH value of HAS in passivating heavy metals limit their application in the passivation of heavy metals in soils. To improve the passivation efficiency of humic acid residues against heavy metals, in this study, modified humic acid residues (N-HAS) were prepared by pretreatment with HNO3 and modification with NH4H2PO4. The results showed that the passivation efficiency of N-HAS was up to 87.75% and 57.07% for Hg and Pb in the effective state, and the adsorption kinetics were under the pseudo-second-order model. The addition of N-HAS to the soil resulted in a change in the morphology of the heavy metals, with the acid extractable state of Hg and Pb reduced by 66.92% and 30.44% respectively, and the results of the Toxicity Leaching Test (TCLP) showed that the addition of N-HAS significantly reduced the leaching toxicity and potential ecological risk index (RI). The soil physicochemical properties changed after the addition of N-HAS and there was a correlation between the soil physicochemical properties and the effective state of Hg and Pb content. In conclusion, N-HAS has a positive effect on the remediation of heavy metal-contaminated soil and has a broad application prospect.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The paper provides a comparative investigation on accuracy and conservation properties of two particle regularization schemes, namely, the Dynamic Stabilization (DS) 1 and generalized Particle ...Shifting (PS) 2 schemes in simulations of both internal and free-surface flows in ISPH (Incompressible SPH) context. The paper also presents an Optimized PS (OPS) scheme for accurate and consistent implementation of particle shifting for free-surface flows. In contrast to PS, the OPS does not contain any tuning parameters for free-surface, consistently resulting in perfect elimination of shifting normal to an interface and resolves the unphysical discontinuity beneath the interface, seen in PS results.
•Accuracy and conservation properties of two particle regularization schemes are comparatively investigated.•The considered particle regularization schemes are dynamic stabilization and particle shifting.•An optimized particle shifting is proposed for free-surface flows.•The optimized particle shifting is free of tuning parameters and eliminates shifting normal to an interface.•The optimized particle shifting outperforms dynamic stabilization in terms of accuracy and energy conservation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The cross-section of carbon fibers (CFs) possessed radial heterostructure, which restricted its mechanical properties. In this paper, heating and γ-irradiation were integrated during PAN fibers ...stabilization process to improve the radial structure of CFs. The synergy between irradiation and heating during stabilization caused the decrease of ID/IG, increase of crystal size, and reduction of pore fractal dimension in whole CFs. Through Raman spectra along fibers cross-section, a radial heterogeneity was found during the whole carbonization process. The combination of γ-irradiation and heating reduced the ID/IG of core part more significantly compared to the skin part of CFs, which weakened radial heterogeneity of CFs. At the same time, it significantly enhanced the tensile strength of CFs. Subsequently, a hierarchy model with three zones containing outer-surface, sub-surface and core parts was presented to explain the evolution of tensile strength for CFs. The γ-irradiation during stabilization enhanced the structure of each part in CFs by generating more cross-linked structures.
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•γ-irradiation in stabilization enhance tensile strength of carbon fibers (CFs).•Three-zone radial heterogeneity model for CFs.•γ-irradiation in stabilization reduce ID/IG and radial heterogeneity of CFs.•Study on micromechanics of CFs by nanoindentation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Aqueous dispersions of graphene oxide are inherently unstable in the presence of electrolytes, which screen the electrostatic surface charge on these nanosheets and induce irreversible aggregation. ...Two complementary strategies, utilizing either electrostatic or steric stabilization, have been developed to enhance the stability of graphene oxide in electrolyte solutions, allowing it to stay dispersed in cell culture media and serum. The electrostatic stabilization approach entails further oxidation of graphene oxide to low C/O ratio (∼1.1) and increases ionic tolerance of these nanosheets. The steric stabilization technique employs an amphiphilic block copolymer that serves as a noncovalently bound surfactant to minimize the aggregate-inducing nanosheet–nanosheet interactions. Both strategies can stabilize graphene oxide nanosheets with large dimensions (>300 nm) in biological media, allowing for an enhancement of >250% in the bioconjugation efficiency of streptavidin in comparison to untreated nanosheets. Notably, both strategies allow the stabilized nanosheets to be readily taken up by cells, demonstrating their excellent performance as potential drug-delivery vehicles.
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IJS, KILJ, NUK, PNG, UL, UM
The changes in the main geotechnical properties (plasticity, unconfined compressive strength, swelling pressure and permeability) associated with the micro level texture and structure of untreated ...and lime-treated compacted FoCa clay samples were studied using X-Ray Diffraction, Thermogravimetric Analysis, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) methods. The TEM was found to be a useful tool in the identification of microscopic changes that arise in the lime-treated FoCa clay in comparison to untreated soil. Based on these studies it was identified that the treated FoCa clay has a greater number of packed layers in comparison to untreated or natural FoCa clay. The TEM technique was also useful to observe the appearance of a cementitious phase or pozzolanic phase that is constituted of a hydrate of calcium silicate aluminate (CSAH). SEM results show changes in the morphology of the clay particles and the concentration of calcium is higher on the border of the particles. The focus of this paper is to provide an explanation of improvements of geotechnical properties that arise in the expansive soil behaviour due to the lime-clay reactions, mainly a pozzolanic reaction, using microscopic analysis.
►The association of XRD, TGA, SEM and TEM analysis reveal the mechanisms of the lime-clay reaction. ►Morphological and structural changes were observed with the different stages of the reaction. Geotechnical properties improved with the progression of the reaction and the formation of new hydrate (CSAH).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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