Thermal nanofluids, the engineered fluids with dispersed functional nanoparticles, have exhibited extraordinary thermophysical properties and added functionalities, and thus have enabled a broad ...range of important applications. The poor dispersion stability of thermal nanofluids, however, has been considered as a longexisting issue that limits their further development and practical application. This review overviews the recent efforts and progresses in improving the dispersion stability of thermal nanofluids such as mechanistic understanding of dispersion behavior of nanofluids, examples of both water-based and oil-based nanofluids,strategies to stabilize nanofluids, and characterization techniques for dispersion behavior of nanofluids. Finally,on-going research needs, and possible solutions to research challenges and future research directions in exploring stably dispersed thermal nanofluids are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The debt crisis of 1982 caused serious economic disruptions in most developing countries. Reform, Recovery, and Growth explains why some of these countries have recovered from the debt crisis, while ...more than a decade later others continue to stagnate. Among the questions addressed are: What are the requirements for a stabilization policy that reduces inflation in a reasonable amount of time at an acceptable cost? What are the effects of structural reforms, especially trade liberalization, deregulation, and privatization, on growth in the short and long runs? How do macroeconomic instability and adjustment policies affect income distribution and poverty? How does the specific design of structural adjustment efforts affect results? In this companion to Macroeconomics of Populism in Latin America, the authors confirm that macroeconomic stability has a positive effect on income distribution. The volume presents case studies that describe in detail the stabilization experiences in Brazil, Israel, Argentina, and Bolivia, and also includes discussion of Chile, Mexico, Peru, and Turkey.
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Polyurethane elastomers have a combination of excellent mechanical, physical and chemical properties along with exceptional biocompatibility. Therefore, these elastomeric systems are ...used in a diverse range of indoor, outdoor, underwater and biomedical applications. However, under certain conditions polyurethane elastomers undergo degradation, resulting in modified properties during usage or even complete failure. The degradation will not only severely affect the quality of the associated items, devices, or instruments, but may also cause catastrophic outcomes risking people’s safety and health. This review presents a comprehensive survey of the literature regarding various types of degradation of polyurethane elastomers, including photo-, thermal, ozonolytic, hydrolytic, chemical, enzymatic, in-vivo/in-vitro oxidative, biological, and mechanical degradation. The stability of polyurethane elastomers based on different building blocks of macrodiols (polyester, polyether, polycarbonate, polybutadiene, and polyisobutylene), isocyanates (aromatic and aliphatic), and chain extenders (diols, triols, and diamines) are summarised, and the mechanisms of different types of degradation are presented. The chemical components significantly influence not only the material structure and properties but also the degradative stability. Focussing on the components, we explore strategies for the enhancement of polyurethane stability through chemistry and engineering. A range of stabilizers, including both organic and inorganic additives for better stability against different types of degradation, are discussed, with a focus on their efficacy and mechanisms of action. A perspective on novel polyurethane materials with desired structures and properties combined with exceptional stability is also provided.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This article studies fixed-time stabilization (FxTS) of a general controllable linear system with an input delay <inline-formula><tex-math notation="LaTeX">\tau</tex-math></inline-formula>. It is ...shown that such a problem is not solvable if the prescribed convergence time <inline-formula><tex-math notation="LaTeX">T_{\tau }</tex-math></inline-formula> is smaller than <inline-formula><tex-math notation="LaTeX">2\tau</tex-math></inline-formula>. For <inline-formula><tex-math notation="LaTeX">T_{\tau }\geq 3\tau</tex-math></inline-formula>, a solution based on linear periodic delayed feedback (PDF) without any distributed delay is established. For <inline-formula><tex-math notation="LaTeX">T_{\tau }>2\tau</tex-math></inline-formula>, a solution based on linear predictor-based PDF containing a distributed delay is proposed. For both cases, the gains of the PDF can be chosen as continuous, continuously differentiable, and even smooth, in the sense of infinitely many times differentiable. If only an output signal is available for feedback, two classes of linear observers with periodic coefficients are designed, so that their states converge to the current and future states of the system at a prescribed finite time, respectively. With the observed current and future states, FxTS can also be achieved by using, respectively, the PDF and observer-based PDF. A linear periodic feedback (without delay) is also established to solve the FxTS problem of linear systems with both instantaneous and delayed controls, which cannot be stabilized by any constant instantaneous feedback in certain cases. Two numerical examples verify the effectiveness of the proposed approaches.
We propose a novel nonlinear control method for solving the problem of stabilization with guaranteed safety for nonlinear systems. The design is based on the merging of the well-known Control ...Lyapunov Function (CLF) and the recent concept of Control Barrier Function (CBF). The proposed control method allows us to combine the design of a stabilizing feedback law based on CLF and the design of safety control based on CBF(s); both of which can be designed independently. Our proposed approach can also accommodate the case of multiple CBFs which correspond to multiple different sets of unsafe states. Lastly, the efficacy of the proposed approach is demonstrated in the simulation results on the stabilization of a nonlinear mechanical system and on the navigation of a mobile robot.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
First‐order organic matter decomposition models are used within most Earth System Models (ESMs) to project future global carbon cycling; these models have been criticized for not accurately ...representing mechanisms of soil organic carbon (SOC) stabilization and SOC response to climate change. New soil biogeochemical models have been developed, but their evaluation is limited to observations from laboratory incubations or few field experiments. Given the global scope of ESMs, a comprehensive evaluation of such models is essential using in situ observations of a wide range of SOC stocks over large spatial scales before their introduction to ESMs. In this study, we collected a set of in situ observations of SOC, litterfall and soil properties from 206 sites covering different forest and soil types in Europe and China. These data were used to calibrate the model MIMICS (The MIcrobial‐MIneral Carbon Stabilization model), which we compared to the widely used first‐order model CENTURY. We show that, compared to CENTURY, MIMICS more accurately estimates forest SOC concentrations and the sensitivities of SOC to variation in soil temperature, clay content and litter input. The ratios of microbial biomass to total SOC predicted by MIMICS agree well with independent observations from globally distributed forest sites. By testing different hypotheses regarding (using alternative process representations) the physicochemical constraints on SOC deprotection and microbial turnover in MIMICS, the errors of simulated SOC concentrations across sites were further decreased. We show that MIMICS can resolve the dominant mechanisms of SOC decomposition and stabilization and that it can be a reliable tool for predictions of terrestrial SOC dynamics under future climate change. It also allows us to evaluate at large scale the rapidly evolving understanding of SOC formation and stabilization based on laboratory and limited filed observation.
Microbial explicit decomposition models have been developed to replace the conventional first‐order model used in most Earth System Models, but their evaluation was limited to observations from laboratory incubations or few field experiments. A comprehensive evaluation of these models is essential using large‐scale in situ observations. We found that, compared to first‐order decomposition model, microbial explicit model more accurately estimates SOC concentrations, microbe/SOC ratio, SOC composition and the sensitivities of SOC stock to changed climate, litter input and soil properties. We support to replace the first‐order decomposition model used in existing Earth System Models with microbial explicit model.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Carbon-supported first-row transition metal complexes drive electroreduction of CO2 to CO in aqueous medium with remarkable activity and selectivity. However, their durability under negative ...potentials is quite low and the deactivation mechanisms are still not clear. Herein, we present an in-depth mechanistic study on the stability of Co porphyrin-based catalysts during CO2 reduction in an aqueous electrolyte. The mechanisms of the degradation reactions were evaluated for Co tetraphenylporphyrin (CoTPP) using a combination of spectral, electrochemical, and theoretical methods. Our evidence shows that two major pathways contribute to the gradual activity loss. The first route is oxidative and yields the catalytically inactive complex CoIIITPPOH. The second pathway is based on reductive carboxylation of the porphyrin ring via transient formation of Co0TPP2– and Co0TPP-CO2–. The latter reaction disrupts the π-system of the porphyrin structure and leads to the complete disintegration of the macrocyclic core. In contrast to the earlier reports, we found that the direct poisoning by CO, demetallation, and reduction to chlorins play no significant role in the deactivation process. It was further determined that the bulky donating functional groups disfavor the formation of dianionic species and restrict access of CO2 to the vulnerable meso-position of the porphyrin ligand, thus improving the catalyst stability. The effect was found to be especially strong for the −OMe-substituted complex CoTPP-(OMe)8 that shows excellent reusability under overpotentials below 500 mV. In turn, electronegative substituents such as fluorine suppress the activity of the catalyst and provide no advantages in terms of durability.
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IJS, KILJ, NUK, PNG, UL, UM
•A hybrid hydrogel (ADPH) composed of ε-Polylysine, polydopamine and agarose was synthesized.•ADPH showed stable photothermal functionality and desirable physicochemical properties.•ADPH possessed ...excellent biocompatibility and photothermal sterilization efficiency.•ADPH significantly promoted wound healing by regulating bacteria-induced inflammation.
Polydopamine (PDA) is emerging as an attractive photothermal agent due to its good photothermal performance and excellent biocompatibility. However, without chemical modification, PDA is normally unstable and usually leached out from the constructed biomaterials, realistically limiting its application space. Here, we constructed a new hydrogel dressing with robust and stable photothermal performance by introduction of ε-Polylysine (ε-PL) into agarose/PDA matrix to efficiently lock PDA. By optimizing PDA/ε-PL rational dose in agarose network structure, a hybrid agarose/PDA/ε-PL hydrogel (ADPH) with stable photothermal functionality and desirable physicochemical properties could be achieved. ADPH possessed satisfactory microbicidal efficacy in vivo, which enabled the bacteria-infected skin wound to be cured quickly by successful suppressing inflammation, accelerating collagen deposition and promoting angiogenesis in a bacterial-infected wound model. Collectively, this study illustrates a simple, convenient but powerful strategy to design functionally stable ADPH dressing for treating dermal wounds, which could open vistas in clinical wound management.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Summary
In this article, we address the problem of achieving predefined‐time control for a class of nonlinear dynamical systems with parameter uncertainties. We introduce an adaptive predefined‐time ...control algorithm based on integrator backstepping for n$$ n $$th order nonlinear systems. Using Lyapunov's stability theory, we establish that the proposed predefined time control approach, combined with an adaptive law, ensures the boundedness of all signals within the closed‐loop system. A notable advantage of our method is its potential to achieve convergence within a predetermined time frame. To validate our approach's efficacy, we present a practical example involving a 2 DOF helicopter, demonstrating the effectiveness of the proposed scheme.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, 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
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