Defined cavities are found in biological systems, such as in enzymes to accelerate specific reactions with specific molecular targets, or as transport containers for molecular cargos. Chemists have ...been inspired by those phenomena found in nature and synthesized defined cage compounds for different purposes, such as for stabilizing reactive intermediates, running reactions within the cavities or studying recognition events. However, most cage compounds are based on the coordination of metal ions, and only a few are charge neutral. Purely organic cages are usually charge neutral and more stable due to existing covalent bonds. Covalent bonds can be made in two ways, applying irreversible reactions or reversible reactions. By introducing dynamic covalent chemistry (DCC), cages have become accessible in good yields from rather simple precursors. Here, we compare both methods and highlight those that give very good yields. Furthermore, the use of organic cage compounds in sorption, recognition, sensing, separation and stabilization of molecules will be discussed.
The synthesis of shape-persistent organic cage compounds
via
reversible and irreversible reactions as well as their use in stabilizing reactive intermediates, recognition of molecules and ions, sensing applications and gas sorption is discussed.
Thermoelectric (TE) materials provide a solid‐state solution in waste heat recovery and refrigeration. During the past few decades, considerable effort has been devoted towards improving the ...performance of TE materials, which requires the optimization of multiple interrelated properties. A fundamental understanding of the interaction processes between the various energy carriers, such as electrons and phonons, is critical for advances in the development of TE materials. However, this understanding remains challenging primarily due to the inaccessibility of time scales using standard atomistic simulations. Machine learning methods, well known for their data‐analysis capability, have been successfully applied in research on TE materials in recent years. Here, an overview of the machine learning methods used in thermoelectric studies is provided, with the role that each machine learning method plays being systematically discussed. Furthermore, to date, the scale of thermoelectric‐related databases is much smaller than those in other fields, such as e‐commerce, image identification, and speech recognition. To overcome this limitation, possible strategies to utilize small databases in promoting materials science are also discussed. Finally, a brief conclusion and outlook are presented.
Thermoelectric materials provide a solid‐state solution in waste heat recovery and refrigeration. A fundamental understanding of the interaction processes between electrons and phonons still remains challenging. An overview of the machine learning methods used in thermoelectric studies is provided, and the role that each machine learning method plays is systematically discussed.
Catalytic conversion of renewable biomass to “green” chemicals and fuel additives has been extensively investigated in the past few decades. Interests on two top platform intermediates for biofuel ...production, i.e. levulinic acid (LA) and 5-hydroxymethylfurfural (HMF), have increased significantly. These two chemicals are generally produced from biomass through acid hydrolysis. This review summarizes the discoveries of the most recent studies on acid-catalyzed hydrolysis, including (i) biomass pretreatment, (ii) glucose production from cellulose hydrolysis, (iii) fructose formation from glucose isomerization, (iv) HMF formation from glucose/fructose dehydration and (v) LA production from HMF rehydration. Humins, the main byproducts, are also discussed in the aspect of their influence on the hydrolysis process, structure, formation mechanism, and applications.
•Reaction mechanism of lignocellulosic biomass to levulinic acid is reviewed.•Challenges for commercial production of 5-hydroxymethylfurfural are studied.•The feasibility of commercial production of levulinic acid is discussed.•Value added conversion pathways of waste hummis are proposed.•Future research direction on biomass acid hydrolysis is recommended.
Using first-principles calculations and deformation potential theory, we investigate the intrinsic carrier mobility (μ) of monolayer MoS2 sheet and nanoribbons. In contrast to the dramatic ...deterioration of μ in graphene upon forming nanoribbons, the magnitude of μ in armchair MoS2 nanoribbons is comparable to its sheet counterpart, albeit oscillating with ribbon width. Surprisingly, a room-temperature transport polarity reversal is observed with μ of hole (h) and electron (e) being 200.52 (h) and 72.16 (e) cm2 V–1 s–1 in sheet, and 49.72 (h) and 190.89 (e) cm2 V–1 s–1 in 4 nm nanoribbon. The high and robust μ and its polarity reversal are attributable to the different characteristics of edge states inherent in MoS2 nanoribbons. Our study suggests that width reduction together with edge engineering provide a promising route for improving the transport properties of MoS2 nanostructures.
Cancer stem cells (CSCs) show a self-renewal capacity and differentiation potential that contribute to tumor progression and therapy resistance. However, the underlying processes are still unclear. ...Elucidation of the key hallmarks and resistance mechanisms of CSCs may help improve patient outcomes and reduce relapse by altering therapeutic regimens. Here, we reviewed the identification of CSCs, the intrinsic and extrinsic mechanisms of therapy resistance in CSCs, the signaling pathways of CSCs that mediate treatment failure, and potential CSC-targeting agents in various tumors from the clinical perspective. Targeting the mechanisms and pathways described here might contribute to further drug discovery and therapy.
Psychological health problems, especially emotional disorders, are common among adolescents. The epidemiology of emotional disorders is greatly influenced by stressful events. This study sought to ...assess the prevalence rate and socio-demographic correlates of depressive and anxiety symptoms among Chinese adolescents affected by the outbreak of COVID-19. We conducted a cross-sectional study among Chinese students aged 12–18 years during the COVID-19 epidemic period. An online survey was used to conduct rapid assessment. A total of 8079 participants were involved in the study. An online survey was used to collect demographic data, assess students’ awareness of COVID-19, and assess depressive and anxiety symptoms with the Patient Health Questionnaire (PHQ-9) and the Generalized Anxiety Disorder (GAD-7) questionnaire, respectively. The prevalence of depressive symptoms, anxiety symptoms, and a combination of depressive and anxiety symptoms was 43.7%, 37.4%, and 31.3%, respectively, among Chinese high school students during the COVID-19 outbreak. Multivariable logistic regression analysis revealed that female gender was the higher risk factor for depressive and anxiety symptoms. In terms of grades, senior high school was a risk factor for depressive and anxiety symptoms; the higher the grade, the greater the prevalence of depressive and anxiety symptoms. Our findings show there is a high prevalence of psychological health problems among adolescents, which are negatively associated with the level of awareness of COVID-19. These findings suggest that the government needs to pay more attention to psychological health among adolescents while combating COVID-19.
At present, the posterior probability measure widely used in English speech recognition has the situation that the posterior probability measure of different phonemes cannot be consistent to measure ...the pronunciation quality of the phoneme and the acoustic modeling method of voice recognition is inconsistent with the evaluation target. Therefore, in order to improve the evaluation effect of English pronunciation quality in colleges and universities, this article is based on artificial emotion recognition and high-speed hybrid model to analyze and filter various clutters that affect speech quality to improve students’ English speech recognition. Moreover, this article uses the characteristics of the clutter and the target in the data to conform to different distributions and based on the clutter distribution characteristics obtained by statistics, this article realizes the suppression of the clutter to improve the target detection performance. In addition, the method proposed in this paper solves the limitations of the clutter suppression technology in the traditional voice detection system and improves the target detection performance. In order to study the pronunciation quality evaluation effect of this model and its effect in English teaching, this paper designs a controlled experiment to analyze the model’s performance. The research results show that the model constructed in this paper has good performance.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Vertical integration of two-dimensional materials has recently emerged as an exciting method for the design of novel electronic and optoelectronic devices. Using density functional theory, we ...investigate the structural and electronic properties of two heterostructures, graphene/phosphorene (G/BP) and hexagonal boron nitride/phosphorene (BN/BP). We found that the interlayer distance, binding energy, and charge transfer in G/BP and BN/BP are similar. Interlayer noncovalent bonding is predicted due to the weak coupling between the p z orbital of BP and the π orbital of graphene and BN. A small amount of electron transfer from graphene and BN, scaling with the vertical strain, renders BP slightly n-doped for both heterostructures. Several attractive characteristics of BP, including direct band gap and linear dichroism, are preserved. However, a large redistribution of electrostatic potential across the interface is observed, which may significantly renormalize the carrier dynamics and affect the excitonic behavior of BP. Our work suggests that graphene and BN can be used not only as an effective capping layer to protect BP from its structural and chemical degradation while still maintaining its major electronic characteristics but also as an active layer to tune the carrier dynamics and optical properties of BP.
2D transition metal dichalcogenides (2D TMDs) (MoS
2
, WS
2
,
etc.
) have attracted considerable attention recently due to their unique structures, strong chemical stability and attractive ...semiconducting characteristics. In particular, these 2D materials have shown great potential for thermal management and thermoelectric energy generation due to their favourable combination of electrical and thermal transport properties, which can lead to a significantly large figure-of-merit. Importantly, recent studies have shown that various approaches, such as chemical functionalization, chemical doping, defect engineering, strain engineering and also forming heterostructures, can further enhance their figure-of-merit (
ZT
). In this article, we review recent advances in the study of the thermoelectric properties of 2D TMDs. We first briefly discuss thermoelectric effects, such as the Peltier and Seebeck effects, the coefficient of performance and figure-of-merit (
ZT
), and point out why TMD materials are ideal candidates for thermal management and thermoelectric applications. Next, we review the progress made in the understanding of the thermoelectric properties of 2D TMDs. Then, we discuss how chemical functionalization, chemical doping, defect engineering, strain engineering, forming heterostructures affect the thermoelectric properties of 2D TMDs. Finally, we present our conclusions and future perspectives.
2D transition metal dichalcogenides (2D TMDs) (MoS
2
, WS
2
,
etc.
) have attracted considerable attention recently due to their unique structures, strong chemical stability and attractive semiconducting characteristics.
The reduced dimensionality makes low-dimensional nanomaterials possessing diverse unusual size-dependent transport properties, due to the distinct quantum confinement, surface and interfacial ...scatterings for electron, photon and phonon at the nanoscale. In this review, we summarize the state-of-the-art studies on the topic of size-dependent phononic thermal transport in low-dimensional nanomaterials, including both theoretical and experimental reports. First, the length-dependent thermal transport in quasi-one-dimensional (quasi-1D) and two-dimensional (2D) nanomaterials are discussed, in which the underlying fundamental physics are correspondingly summarized. Then, we review the various effects of transverse dimensions on the thermal conductivity, including the diameter effect in nanowires, and the thickness and width effects in 2D sheets and nanoribbons. Finally, considering the significant importance of interfacial thermal resistance in nanoscale devices due to the increased density of interface, the size effect on the interfacial thermal resistance and thermal rectification is also discussed. The basic concept of phononic engineering to control the interfacial thermal resistance and also the detailed phonon scattering mechanisms are summarized. This perspective review would provide basic and advanced knowledge to understand and utilize the size-dependent thermal transport in nanomaterials, which will be beneficial to the further understanding of energy transport and conversion in the low-dimensional quantum devices.
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