This article aims to delve into the role of boredom on students' engagement which has always attracted attention in that it is one of the most common academic feelings felt by students that causes ...them to feel more or less enthusiastic to engage in class activities, and there is a growing increase in such feelings among adolescents; therefore, its various dimensions should be taken into consideration. First and foremost, a variety of definitions from different points of view have been proposed. Then, with a focus on the distinction between state boredom and trait boredom which is one of the most radical classifications of boredom it has been continued. Following that, the antecedents of boredom are additionally taken into consideration along with the role of boredom in students' engagement that necessitates a few changes in the curriculum of schools. Moreover, some coping strategies on how to overcome boredom have been featured. Finally, in the discussion part, the emphasis of the points, which have been mentioned above, in the learning context for both teachers and students has been discussed, and new suggestions for further studies have been proposed.
The construction of an aryl ketone structural unit by means of catalytic carbon-carbon coupling reactions represents the state-of-the-art in organic chemistry. Herein we achieved the direct ...deoxygenative ketone synthesis in aqueous solution from readily available aromatic carboxylic acids and alkenes, affording structurally diverse ketones in moderate to good yields. Visible-light photoredox catalysis enables the direct deoxygenation of acids as acyl sources with triphenylphosphine and represents a distinct perspective on activation. The synthetic robustness is supported by the late-stage modification of several pharmaceutical compounds and complex molecules. This ketone synthetic strategy is further applied to the synthesis of the drug zolpidem in three steps with 50% total yield and a concise construction of cyclophane-braced 18-20 membered macrocycloketones. It represents not only the advancement for the streamlined synthesis of aromatic ketones from feedstock chemicals, but also a photoredox radical activation mode beyond the redox potential of carboxylic acids.
Wind forcing injects energy into mesoscale eddies and near-inertial waves (NIWs) in the ocean, and the NIWs are believed to solve the puzzle of mesoscale energy budget by absorbing energy from ...mesoscale eddies. This work studies the turbulent energy transfer in the NIW–quasigeostrophic mean mesoscale eddy coupled system based on a previously derived two-dimensional model which inherits conserved quantities in Boussinesq equations (Xie & Vanneste, J. Fluid Mech., vol. 774, 2015, pp. 147–169). The conservation of energy, potential enstrophy and wave action implies the existence of phase transition with a change of the relative strength between NIW and mean-flow, quantified by a parameter $R$. By running forced-dissipative numerical simulations, we justify the existence of second-order phase transition around a critical value $R_c$. When $0<R<R_c$, energy transfers bidirectionally, wave action transfers downscale and vorticity forms strong cyclones. When $R>R_c$, energy transfers downscale, wave action transfers bidirectionally and vortex filaments are dominant. We find the catalytic wave induction mechanism where the NIW induces a downscale energy flux of the mean flow, which differs from the stimulated loss of balance mechanism observed in inertial value problems. In the parameter regime $0<R<R_c$, catalytic wave induction is similar to the stimulated loss of balance as the downscale energy transfer is proportional to the NIW energy injection, however, catalytic wave induction has a distinct feature of the absence of energy conversion from mesoscale eddies to NIWs. The new mechanism is effective in the toy-model study, making it potentially important for ocean energetics.
Visible-light photoredox catalysis has been esteemed as one sustainable and attractive synthetic tool. In the past four years, a new yet challenging trend, visible-light-driven redox-neutral radical ...C-C cross-coupling involving putative radical intermediates, has been booming rapidly. Its advent brings a powerful platform to achieve non-classical C-C connections, and should lead to fundamental changes in retrosynthetic analysis. In this tutorial review, we highlight the recent achievements of visible-light-mediated redox-neutral radical C(sp
3
)-C(sp
2
), C(sp
3
)-C(sp), and C(sp
3
)-C(sp
3
) bond formation, opening a new window for C-C cross-coupling through the photoredox electron shuttling cycle between two coupling partners. While radical-radical coupling steered by the persistent radical effect was proposed as a rational explanation for the redox-neutral photoredox events, alternative kinetically driven chain propagation and radical addition pathways cannot be ruled out. This tutorial review aims to highlight the recent achievements of photoredox-neutral radical C-C coupling in synthetic chemistry.
Visible-light-driven redox-neutral radical C-C coupling brings a powerful platform to achieve non-classical C-C connection in the absence of external reductants or oxidants through a photoredox electron shuttling cycle.
In recent years, visible-light-mediated C–H bond functionalization has become an emerging field at the forefront of organic synthesis. It is of considerable interest to academic and industrial ...chemists owing to the atom/step economical features as well as the overall sustainability. In this Letter, we mainly discussed the recent typical examples in sp2 and sp3 C–H bond functionalization by means of visible-light photoredox catalysis.
C-H bonds are ubiquitous in organic molecules. Homogenous gold-catalyzed direct functionalization of unsaturated C-H bonds has emerged as a powerful method in our synthetic toolbox. However, C
sp
3
...-H bonds have larger dissociation energy and lower proton acidity, and thus the efficient and exquisitely selective cleavage of this kind of chemical bonds for the formation of new carbon-carbon and carbon-heteroatom bonds is still a great challenge. In this tutorial review, we will highlight the recent achievements of gold-catalyzed oxidative and redox-neutral C
sp
3
-H bond functionalization, which opens new avenues for economical and sustainable construction of fine chemicals.
Homogeneous gold-catalyzed sp
3
C-H bond functionalization strategy opens a new avenue for economical and sustainable construction of fine chemicals.
The rapidly growing demand for humidity sensing in various applications such as noninvasive epidermal sensing, water status tracking of plants, and environmental monitoring has triggered the ...development of high-performance humidity sensors. In particular, timely communication with plants to understand their physiological status may facilitate preventing negative influence of environmental stress and enhancing agricultural output. In addition, precise humidity sensing at bio-interface requires the sensor to be both flexible and stable. However, challenges still exist for the realization of efficient and large-scale production of flexible humidity sensors for bio-interface applications. Here, a convenient, effective, and robust method for massive production of flexible and wearable humidity sensor is proposed, using laser direct writing technology to produce laser-induced graphene interdigital electrode (LIG-IDE). Compared to previous methods, this strategy abandons the complicated and costly procedures for traditional IDE preparation. Using graphene oxide (GO) as the humidity-sensitive material, a flexible capacitive-type GO-based humidity sensor with low hysteresis, high sensitivity (3215.25 pF/% RH), and long-term stability (variation less than ± 1%) is obtained. These superior properties enable the sensor with multifunctional applications such as noncontact humidity sensing and human breath monitoring. In addition, this flexible humidity sensor can be directly attached onto the plant leaves for real-time and long-term tracking transpiration from the stomata, without causing any damage to plants, making it a promising candidate for next-generation electronics for intelligent agriculture.
Display omitted
•A convenient, effective, and robust method for massive production of flexible and wearable humidity sensor is developed based on laser-induced technology.•A flexible capacitive-type GO-based humidity sensor with low hysteresis, high sensitivity, and long-term stability is obtained.•The fabricated flexible and wearable sensor can be used for noncontact humidity sensing and human breath monitoring.•Real-time and long-term tracking of plant transpiration at bio-interface in realized without causing any physical damage to plants.
Radical deuteration Li, Nian; Li, Yantao; Wu, Xiaopeng ...
Chemical Society reviews,
08/2022, Letnik:
51, Številka:
15
Journal Article
Recenzirano
Deuterated chemicals are becoming irreplaceable in pharmaceutical engineering, material science and synthetic chemistry. Many excellent reviews have discussed acid/base-dependent or metal-catalyzed ...deuteration reactions, but radical deuterations have been discussed less. With the development of radical chemistry, there has been a rapid growth in radical deuterium-labelling technology. Diverse mild, cheap and efficient strategies for deuterium atom installation have been reported, and this review summarizes the recent achievements of radical deuteration classified by the reaction types.
This review is a systematic summary of radical deuteration with four reaction types: reductive deuteration, defunctionalization-deuteration, hydrogen-deuterium (H/D) exchange and radical deuteroalkylation.
Human action recognition is an important branch among the studies of both human perception and computer vision systems. Along with the development of artificial intelligence, deep learning techniques ...have gained remarkable reputation when dealing with image categorization tasks (e.g., object detection and classification). However, since human actions normally present in the form of sequential image frames, analyzing human action data requires significantly increased computational power than still images when deep learning techniques are employed. Such a challenge has been the bottleneck for the migration of learning-based image representation techniques to action sequences, so that the old fashioned handcrafted human action representations are still widely used for human action recognition tasks. On the other hand, since handcrafted representations are usually ad-hoc and overfit to specific data, they are incapable of being generalized to deal with various realistic scenarios. Consequently, resorting to deep learning action representations for human action recognition tasks is eventually a natural option. In this work, we provide a detailed overview of recent advancements in human action representations. As the first survey that covers both handcrafted and learning-based action representations, we explicitly discuss the superiorities and limitations of exiting techniques from both kinds. The ultimate goal of this survey is to provide comprehensive analysis and comparisons between learning-based and handcrafted action representations respectively, so as to inspire action recognition researchers towards the study of both kinds of representation techniques.
•We provide a comprehensive stud over the state-of-the-art action representations.•Deep learning-based representations are compared to handcrafted representations.•Pros and cons of current deep learning-based approaches are discussed.
The main object of this paper is to construct a new generalization of the Bernstein operator, depending on a non-negative real parameter. We investigate some elementary properties of this operator, ...such as end point interpolation, linearity and positivity, etc. By using these generating operators, we provide another proof of the Weierstrass Approximation Theorem. We give the detailed proofs to the rate of convergence and Voronovskaja type asymptotic estimate formula for the operators. Moreover, an upper bound for the error is obtained in terms of the usual modulus of continuity. Shape preserving properties of the generalized Bernstein operators are also studied. It is proved that monotonic or convex functions produce monotonic or convex generalized Bernstein polynomials.
PDF
