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.
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.
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.
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•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.
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.
In this article, a class of low-profile dual-band circular polarizers based on aperture-coupled patch resonators (ACPRs) are proposed to achieve versatile linear-to-circular polarization (LP-to-CP) ...conversions. Initially, a dual-band dual-polarized bandpass frequency-selective surface (FSS), consisting of a composite array of two independent ACPRs subelements, is presented to obtain the desired transmission properties for vertically and horizontally polarized incident waves. The equivalent circuit model is then introduced to analyze the proposed FSS, exhibiting that transmission magnitude properties of vertically and horizontally polarized transmitted waves can be independently designed within these two passbands. Furthermore, two pairs of rectangular slots are introduced in the patches of these ACPRs subelements and extensively investigated to demonstrate that versatile phase differences between vertically and horizontally polarized transmitted waves with equal magnitude can be achieved. Based on this concept, within these two passbands, a right- or left-hand circularly polarized (RHCP or LHCP) transmitted wave is then attained by designing the vertical and horizontal components of a 45° tilted LP incident wave with equal magnitudes and ±90° phase difference, thus leading to dual-band LP-to-CP polarization conversions. To validate the design concept, two prototypes of dual-band circular polarizers with orthogonally and identically LP-to-CP conversions in each operation band are designed, fabricated, and measured. Experimental results have well revealed that our proposed structure has a few attractive advantages of ultrathin profile, low axial ratio, and flexible designs in LP-to-CP conversions and frequency band ratios.
Abstract
The ketone functional group has a unique reactivity in organic chemistry and is associated with a number of useful reactions. Catalytic methods for ketone synthesis are continually being ...developed. Here, we report a photoredox, nickel and phosphoranyl radical synergistic cross-electrophile coupling of commercially available chemicals, aromatic acids and aryl/alkyl bromides. This allows for concise synthesis of highly functionalized ketones directly, without the preparation of activated carbonyl intermediates or organometallic compounds, and thus complements the conventional Weinreb ketone synthesis. Use of the appropriate photocatalyst, ligand amount and solvents can match the reaction rate required by any simple catalytic cycle. The practicality and synthetic robustness of the reaction are illustrated by the facile synthesis of complex ketones from readily available feedstock chemicals.
The development of high-performance and cost-effective electrocatalysts is of great significance for hydrogen production by water splitting but remains challenge. Herein, a metal organic frameworks ...(MOFs) templating approach is proposed to synthesize Co incorporating FeP nanotubes (Co-Fe-P nanotubes) for efficient for hydrogen evolution reaction (HER). The MOFs-derived tubular structure with in situ Co substitution lead to abundant catalytic sites, fast mass and charge transport pathways, and desirable electronic configuration. These beneficial effects enable Co-Fe-P nanotubes efficient HER catalytic activity in a wide pH range, achieving small overpotentials of 86, 138, and 66 mV at a current density of 10 mA cm−2 in 1 M KOH, 1 M phosphate buffer solution (PBS), and 0.5 M H2SO4, respectively. The catalytic activity of Co-Fe-P nanotubes outperforms most of the reported FeP-based electrocatalysts. Density functional theory calculations further reveal that Co substitution results in increased density of states near Fermi level, boosting the intrinsic electrocatalytic activity of Co-Fe-P nanotubes. This work affords a feasible way to the synthesis of cheap and efficient FeP-based electrocatalysts for HER.
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•Co-Fe-P nanotubes are synthesized by a MOFs templating approach.•The Co-Fe-P electrocatalysts show excellent HER catalytic activity in wide pH range.•The tubular nanostructure of Co-Fe-P is crucial for the superior HER performances.•Desirable electronic states for efficient HER are achieved by Co incorporation.
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