C–H bond activation and decarboxylation are two significant processes in organic synthesis. The combination of these processes provides a novel synthetic strategy, that is, decarboxylative C–H bond ...functionalization. Considerable attention has been focused on such an active research field. This review offers an overview of the utility of decarboxylative C–H bond functionalization in the synthesis of various organic compounds, such as styrenes, chalcones, biaryls, and heterocycles, covering most of the recent advances of the decarboxylative functionalization of Csp–H, Csp2–H, and Csp3–H bonds, as well as their scopes, limitations, practical applications, and synthetic potentials.
We describe here a 3+3-type condensation reaction of O-acetyl ketoximes and α,β-unsaturated aldehydes that is synergistically catalyzed by a copper(I) salt and a secondary ammonium salt (or amine). ...This redox-neutral reaction allows modular synthesis of a variety of substituted pyridines under mild conditions with tolerance of a broad range of functional groups. The reaction is driven by a merger of iminium catalysis and redox activity of the copper catalyst, which would initially reduce the oxime N–O bond to generate a nucleophilic copper(II) enamide and later oxidize a dihydropyridine intermediate to the pyridine product.
Quasi-zero stiffness system has been widely used to isolate structural vibrations. However, its small dynamic stiffness may result in drastic low-frequency vibration. This is a curse of employing ...quasi-zero stiffness systems in engineering. In this paper, a nonlinear energy sink (NES) is used to overcome this difficulty. In order to reduce the additional weight of the NES, the mass of the NES is replaced by an inerter. By superposing the quasi-zero stiffness system and the inertial NES together, a combined vibration control technique is proposed. The equations of the motion of the primary structure and the combined control system are established. The steady-state response of the system is solved by the harmonic balance method and verified numerically. The suppression performance is evaluated based on the resonance suppression efficiency and the effective vibration isolation bandwidth. In addition, the parameters of the inertial NES are optimized. The results show that the combined control system has a better vibration control effect than the quasi-zero stiffness isolator. Specifically, the combined control system provides a smaller resonance amplitude and a wider vibration isolation band. In summary, the combined control scheme has both effects of the nonlinear isolation and the nonlinear absorption. Therefore, this paper proposes a vibration control technique that can achieve a wide band of vibration isolation and small vibration amplitude with a very little additional mass.
For simulating phase change process of pure solid gallium, previously published literature contains some key problems, including the inappropriate definition & computation for interface errors, and ...the unsatisfactory numerical verifications & validations. Herein, the 2D verifications and 2D validations for the enthalpy-porosity modeling of pure gallium melting starting from a vertical end wall have been reported comprehensively. The well-known and classic experimental data presented in literature are used to verify and validate the model. The groundbreaking contributions in this work are that: i) The definition and computational method of the interface-position errors between the numerical and experimental results are revisited and proven carefully; ii) The numerical schemes as well as major parameters of 2D modeling gallium melting are selected with overall interface error <9%. However, these schemes and parameters are not appropriate for the solidification modeling of gallium due to the irregular and non-reproducible interface shapes caused by highly anisotropic properties of solid crystal gallium as experimentally reported in literature; iii) The 2D validations of enthalpy-porosity modeling of gallium melting are investigated in detail, and the maximum interface error is within the limits of ±12%. Moreover, the simulated liquid volume fractions and dimensionless heat transfer coefficients are well correlated in terms of related criteria parameters, and they are compared with correlations available in literature. It is concluded that to solidly validate the modeling of pure metal melting, both the global parameters (e.g., volume-averaged liquid fraction) and the local parameters (e.g., interface position) need to be considered together.
•Revisit definition and computational method of local interface error.•Define evaluation indexes of global interface-position errors synthetically.•Clarify numerical schemes and key parameters of 2D modeling gallium melting.•Validate 2D enthalpy-porosity modeling melting by literature's experimental data.
Literature survey found that three important scientific problems including: i) The feasibility of 2D modeling was not be further validated by compared the 3D & 2D simulations with the famous classic ...experiments of literature; In literature's work, ii) the plus exponent of the aspect ratio in liquid-fraction correlation is questionable, and iii) how to calculate the Mean Liquid Layer Thickness (lc) was not mentioned and/or discussed that would lead to get the value of lc-based Nusselt number difficultly. Therefore, in this work, the 3D validation and 2D feasibility are roundly reported as compared by all the experimental data of literature. The novel results and core findings in the paper are that: i) It is confirmed that the present 3D simulation on pure gallium melting by enthalpy-porosity technique is completely validated, and 3D simulation can be replaced by 2D one, and it also should be replaced by 2D due to high running time ratio nearly from 17 to 27 times depended powerfully on the aspect ratio of computational domain; Thereinto, ii) the sign of the aspect-ratio exponent shown in the correlation equation of Liquid fraction vs. Stefan number of literature is clarified and corrected, and iii) the correlation of lc is now well-proposed to calculate the lc-based Nusselt number directly and quickly, and then the developed lc's correlation is commented from multi-points of views. Finally, the discrepancy sources between current 3D & 2D modeling and literature's experimental measuring on the pure solid‑gallium phase change are discussed and summarized in detail. It should be mentioned that the currently obtained new results and novel findings will promote the new understandings and high efficiency applications in related fields, e.g., transient cooling of high heat-flux electronic devices in aerospace and navigation that would be researched in the future.
•Validate 3D enthalpy-porosity modeling pure gallium melting completely.•Illuminate feasibility on 3D simulation replaced by 2D simplification strictly.•Correct aspect-ratio exponent in literature's liquid-fraction correlation as negative.•Develop correlation of mean liquid layer thickness to calculate Nusselt number.
•Lower double fin is proposed to enhance the PCM melting.•Impacts of the double-fin parameters and HTF temperature are examined.•Characteristics of lower double fin on PCM melting enhancement are ...analyzed.•Outer tube conductivity has a great impact on melting behavior and fin arrangement.
Latent heat thermal energy storage (LHTES) with novel fin configuration to enhance heat transfer was proposed. The fins were placed in the lower half of the LHTES unit and were symmetrical along the vertical centerline. A transient two-dimensional numerical model was developed to study the melting characteristics of lauric acid (phase change material, PCM). The local double-fin at different fined angles (θ = 30°, 60°, 90°, 120°, 150° and 180°) were investigated and the results were compared with the uniform double-fin (base case), in which the two fins were placed on the top and bottom. It was found that with special θ, using local double-fin can greatly enhance melting than using the uniformly arranged. The effects of shell conductivity, dimensionless fin length (l) and heat-transfer fluid temperature on PCM melting were investigated. Results showed that the conductivity of shell had a remarkable effect on the melting behaviors and the performance of local double-fin. The complete melting time for the optimum θ can be saved by 66.7% when the dimensionless fin length increases from 0.50 (optimum at θ = 30°) to 1.00 (optimum at θ = 120°). The complete melting time decreases by 53.1% when heat-transfer fluid temperature increases from 333.15 to 353.15 K under l = 1.00 and θ = 120° Furthermore, it was found that the use of longer fins can improve the LHTES performance more greatly for the local double-fin than that of the base case.
Recent advances in the pathophysiologic understanding of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has indicated that patients with severe coronavirus disease 2019 ...(COVID-19) might experience cytokine release syndrome (CRS), characterized by increased interleukin (IL)-6, IL-2, IL-7, IL-10, etc. Therefore, the treatment of cytokine storm has been proposed as a critical part of rescuing severe COVID-19. Several of the cytokines involved in COVID-19 employ a distinct intracellular signaling pathway mediated by Janus kinases (JAKs). JAK inhibition, therefore, presents an attractive therapeutic strategy for CRS, which is a common cause of adverse clinical outcomes in COVID-19. Below, we review the possibilities and challenges of targeting the pathway in COVID-19.
Recent advances in the pathophysiologic understanding of COVID-19 infection have suggested a critical role of cytokine release syndrome (CRS) in severe COVID-19 patients.Several inflammatory cytokines that are involved in CRS and correlate with adverse clinical outcomes in COVID-19 employ a distinct intracellular signaling pathway mediated by Janus kinases (JAKs).JAK-STAT signaling may be an excellent therapeutic target for the development of much needed therapies for COVID-19.
The aim of the study is to create and validate a model of the relationship between specialization in leisure activities, the individual's adaptation to the environment and the heart flow experience. ...In order to clarify the role of the individual's adaptation to the environment in the relationship between specialization in leisure activities and the heart flow experience. The study utilized purposive sampling, cluster sampling, and random sampling. Using questionnaires and interviews to survey 525 cycling enthusiasts. Descriptive analysis, model construction and testing of the constructed path relationships were conducted using SPSS 20.0 and Amos 20.0. The results indicate that the model of the relationship between recovery specialization, individual-environment fit and heart flow experience has a good overall fit. The model shows good reliability and validity. Cyclists' recreational specialization has a statistically significant effect on individual-environment fit (β = 0.38, P < 0.001). The fit between individual and environment has a statistically significant influence on the heart flow experience (β = 0.39, P < 0.001). The fit between individual and environment serves as a mediating variable between recreational specialization and the heart flow experience, with the path showing statistical significance (β = 0.15, P < 0.001). Recreational specialization has a statistically significant effect on the heart flow experience (β = 0.30, P < 0.001). And the overall path of the effects of recreational specialization of cyclists on the fit between individual and environment is (β = 0.45, P < 0.001), with the path showing statistical significance.
The stronger the recreational specialization of cyclists and the greater the fit between individual and environment, the stronger their heart flow experience. The fit between individual and environment plays a partially mediating role.
Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an ongoing global health emergency. Here we highlight nine most important research ...questions concerning virus transmission, asymptomatic and presymptomatic virus shedding, diagnosis, treatment, vaccine development, origin of virus and viral pathogenesis.
Literature survey showed that three important and key scientific problems including: i) the mechanisms or underlying causes of the discrepant sources, especially at the top phase interfaces, are yet ...to be investigated, which are crucial to recognize the validation of the numerical technology for metal isothermal phase-change applications. Moreover, revisiting the well-known experiments in literature, they did ii) not display the interface shape under the conditions of aspect ratio = 0.714 & Stefan number = 0.0391 at the dimensionless time of 0.0184, but also iii) not discuss the equilibrium state of pure solid‑gallium phase change. Therefore, it is a fascinating and interesting concern that what happened for these two kinds of important problems or key questions ii) and iii). Here, all above-mentioned three problems i) to iii) are explored and addressed by finite-volume-based enthalpy-porosity methodology. The core findings in this work are that: i) The novel mechanisms of convective false diffusion are revealed and clarified for enthalpy-porosity modeling solid-liquid interface of pure solid‑gallium melting; ii) The novel phenomena of asymmetrical solid-liquid interface are found and explained for a large aspect ratio of 0.714; iii) The innovative findings and fitting correlations are discussed by extended literature’s study to phase-change equilibrium state, and it is comprehensively demonstrated that the dimensionless correlation of mean liquid layer thickness is equivalent to that of global liquid volume fraction.
•Clarify novel mechanisms of convective false diffusion in modeling phase interface.•Explain novel phenomena of asymmetrical interface even if geometry & boundary conditions are symmetric.•Extend literature's study with innovative findings of phase-change equilibrium state.•Find correlation of mean liquid layer thickness closes to that of liquid fraction.
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