Display omitted
A Sc(OTf)3-catalyzed diastereoselective 4 + 2 cycloaddition reaction of 3-benzylideneindoline-2-thiones with 2-alkylidene malonates has been realized, leading to biologically ...important indole-annulated thiopyran derivatives in moderate to good yields. Moreover, a gram-scale reaction and chemical transformation of the cycloadduct into a sulfone were carried out to further extend the synthetic utility.
In this study, a novel ultra-high-performance concrete (UHPC) composite plate that is reinforced with a fibre-reinforced polymer (FRP) grid (herein FRP-UHPC composite plate) is developed and ...reported. The durability and mechanical performance of FRP-UHPC composite plates in harsh environments are expected to be superior to conventional materials when used in optimal configurations; because i) both UHPC and FRP composites in isolation have excellent mechanical properties in specific directions, and ii) they are also durable materials. The flexural and tensile behaviour of FRP-UHPC composite plates, with and without the inclusion of steel fibres in the UHPC mix, were investigated via experimentation. The test results, which demonstrate the excellent interaction between FRP and UHPC, confirm the viability of the system: i) the inclusion of an FRP grid enhances the ultimate flexural capacity by over 150% and the ultimate tensile capacity by over 200%; ii) the FRP-UHPC composite plates exhibit tensile elastic-strain hardening behaviour and the average ultimate tensile stress of the composite plates with an FRP reinforcement ratio of about 0.69% is over 25 MPa; and iii) the interaction between the FRP grid and UHPC is sufficient to transfer stresses in the longitudinal FRP strips to the UHPC through the transverse strips of the FRP grid, while the steel fibres in the UHPC passing through the openings of the FRP grid reduce the likelihood of FRP debonding. The proposed strain-hardening FRP-UHPC plates are expected to be promising for structural elements with various purposes.
The study takes 10 urban agglomerations in China as the research object, focusing on the Chengdu-Chongqing urban agglomeration, and applies Data Envelopment Analysis (DEA) to measure and compare ...their scientific input and output efficiency of universities. First, this paper analyzes the input and output of scientific research in universities in major provinces in China in detail. Second, according to the construction principles of the indicator system, using qualitative interview to construct evaluation indicators of university research efficiency. Third, using DEA method, first analyze the input and output profile of some urban agglomeration universities such as Chengdu-Chongqing economic circle, measure and compare their research input and output efficiency, then compare and analyze the research efficiency of research-type sample universities within Chengdu-Chongqing economic circle, and conduct a projection study of non-DEA effective sample universities. The main conclusions are as follows: first, the average efficiency of scientific research in universities in Chengdu-Chongqing and other urban agglomerations in 2020 has slightly increased compared with that in 2016, but the gap between urban agglomerations is prominent, and the innovation level of scientific research in higher education institutions in urban agglomerations needs to be improved. Second, there is a mismatch between the themes of research, funding and human resources in research-oriented universities in the Chengdu-Chongqing economic circle. Third, there is considerable room for improvement in research efficiency, and the influence of scale on overall efficiency is weak. We found that excessive investment in scientific research in universities is the main reason for the non-effect.
Fiber reinforced polymer (FRP) reinfrocement has been proposed to be reinforcement in ultra-high performance concrete (UHPC) so as to avoid the post-peak strain softening behavior of UHPC under ...tension and to reduce the fiber dosage used in UHPC. In this paper, tubular beams made by FRP grid-reinforced UHPC composites (referred to as FRP-UHPC compoistes or simply FUC) have been proposed and ten FUC tubular beams were tested under shear loading. Effects of the shear span ratio, the fiber type (polyethylene (PE) fibers and steel fibers) on the shear behavior of FUC tubular beams were investigated. Results reveal that the proposed FUC tubular beams have an excellent ultimate strength and a ductile behavior under shear. A theoretical model based on the truss-arch theory is proposed for predicting the shear capacity FUC tubular beams, and its accuracy is verified against the test results.
Selenium (Se) is an important trace mineral having many essential roles at the cellular and organismal levels in animal and human health. The biological effects of Se are mainly carried out by ...selenoproteins (encoded by 25 genes in humans and 24 in mice). As an essential component of selenoproteins, Se performs structural and enzymic roles; in the latter context it is well known for its catalytic and antioxidative functions. Studies involving different animal models have added great value to our understanding regarding the potential implications of Se and selenoproteins in mammalian fertility and reproduction. In this review, we highlight the implications of selenoproteins in male fertility and reproduction followed by the characteristic biological functions of Se and selenoproteins associated with overall male reproductive function. It is evident from observations of past studies (both animal and human) that Se is essentially required for spermatogenesis and male fertility, presumably because of its vital role in modulation of antioxidant defense mechanisms and other essential biological pathways and redox sensitive transcription factors. However, bearing in mind the evidences from mainstream literature, it is also advisable to perform more studies focusing on the elucidation of additional roles played by the peculiar and canonical selenoproteins i.e., glutathione peroxidase 4 (GPX4) and selenoprotein P (SELENOP) in the male reproductive functions. Nevertheless, search for the elucidation of additional putative mechanisms potentially modulated by other biologically relevant selenoproteins should also be included in the scope of future studies. However, as for the implication of Se in fertility and reproduction in men, though a few clinical trials explore the effects of Se supplementation on male fertility, due to inconsistencies in the recruitment of subjects and heterogeneity of designs, the comparison of such studies is still complicated and less clear. Therefore, further research focused on the roles of Se and selenoproteins is awaited for validating the evidences at hand and outlining any therapeutic schemes intended for improving male fertility. As such, new dimensions could be added to the subject of male fertility and Se supplementation.
Different from the typical bi-linear stress–strain response, many recent studies have reported a stress reduction-recovery response (i.e., a three-segment behavior of strain ...hardening-softening-hardening) for fiber reinforced polymers (FRP)-confined concrete in stub columns, which might have detrimental effects on column performance (e.g., excessive deformation or instability). Therefore, the purpose of this paper is to conduct a state-of-the-art review on the stress reduction-recovery behavior of FRP-confined concrete in stub columns, particularly focusing on exploring the underlying causes. Five major root causes for stress reduction have been identified: (1) concrete core brittleness; (2) concrete core shrinkage; (3) non-uniform confinement due to the column shape; (4) insufficient confinement due to the characteristics of FRP materials or fiber orientations; and (5) the arching action. In addition, current strategies for mitigating stress reduction have also been summarized. Although increasing FRP confinement level is a common method, it has little effect for FRP partially confined concrete, for which reducing the area of exposed concrete is more effective. Moreover, increasing steel fiber content in concrete could mitigate stress reductions for columns with brittle concrete cores, while increasing corner radius ratio is more efficient for columns with non-circular shapes (i.e., square and rectangular columns). Furthermore, the hybrid use of small and large rupture strain FRP wraps and the optimum stacking of FRP wraps with different fiber orientations could enhance the FRP confinement and thus alleviate the stress reduction. By establishing a new database containing 317 datasets with stress reduction-recovery response, the performances of six three-segment design-oriented models were assessed. Other than discussing the weakness and strength of these models based on the assessment results, future directions in deriving more accurate models for FRP-confined concrete columns were also outlined.
In this article, an ultrahigh step-up quadratic boost converter based on coupled-inductor is proposed. The voltage gain of the proposed converter can be enhanced significantly by increasing the duty ...cycle due to the quadratic boost structure. A coupled-inductor integrated with a voltage doubler cell is applied to further improve conversion ratio and reduce voltage stresses. The leakage inductor current is utilized to achieve zero-current switching for output diode . Meanwhile, high efficiency is possible as the energy of the leakage inductor is recycled and transferred to the load. The operating principle and steady-state analysis are provided, and a 280-W prototype is designed to verify the validity of the proposed converter.
The regioselective ring‐opening of 1,2‐ and 1,3‐sulfamidates with fluorine anion is reported. Direct construction of monofluoro‐substituted amines and amino acid derivatives using inexpensive and ...easily available potassium fluoride (KF). The monofluorination process only needs 35 minutes under heating, which will be an attractive route for the synthesis of the PET fluorine‐18 radiotracer. The application of the product can be extended to the construction of fluorinated polypeptides after simple deprotection treatment.
The regioselective ring‐opening of 1,2‐ and 1,3‐sulfamidates with fluorine anion is reported. Construction of monofluoro‐substituted amines and amino acid derivatives is realized by using inexpensive potassium fluoride (KF). The monofluorination process only needs 35 minutes under heating, which will be an attractive new route for the synthesis of the PET fluorine‐18 radiotracer.
In this paper, we propose a profit-maximization-based pricing optimization model for the demand response (DR) management with customer behavior learning in the context of smart grids. By recognizing ...the different consumption patterns between shiftable and curtailable appliances, two different and distinguished behavior models are proposed. For shiftable appliances whose energy consumption can be shifted from high price periods to low price periods but total energy consumption is fixed, a probabilistic behavior model and its learning algorithm are proposed to model an individual customer's shifting probabilities dependent on different hourly prices. For curtailable appliances whose energy consumption cannot be shifted but total energy consumption can be adjusted, a regression model is proposed to model an individual customer's usage patterns dependent on prices and temperatures. After proposing the learning algorithms to identify these proposed behavior models, this paper further develops a genetic algorithm-based distributed pricing optimization algorithm for DR management with the aim to maximize the retailer's profit. Numerical results indicate the applicability and effectiveness of the proposed models and their benefits to the retailer by improving its profit.
•Compressive behavior of heat-damaged square concrete columns confined with BFRP jackets was investigated.•Effects of exposure temperature and BFRP jacket layers on the experimental results were ...studied.•The confinement mechanism of BFRP-confined heat-damaged concrete was discussed.•The accuracy of typical confinement models for FRP-confined heat-damaged concrete was examined.
Externally bonded fiber-reinforced polymer (FRP) composites are increasingly used to confine concrete columns as an effective strengthening technique. During the past two decades, a significant research effort has focused on the performance of FRP-strengthened concrete structures under fire exposure. However, there is still a lack of research on the structural behavior of heat- or fire-damaged concrete structures repaired with FRP composites. This paper presents the results of the first-ever experimental study on the compressive behavior of heat-damaged square concrete prisms that are either unconfined or confined by a promising type of FRP composites made of basalt fibers. A total of 51 specimens were prepared and tested under axial compression. The design variables included the heat-induced damage levels of concrete prisms after exposure to various elevated temperatures (200, 400, 600 and 800 °C) and the layers of basalt FRP (BFRP) jackets (2-, 3- and 4-layer) used for strengthening. The failure modes, compressive strengths, ultimate axial strains, axial stress–strain curves, and axial strain-to-hoop strain relationships of the specimens were investigated and compared. The external confinement of the BFRP jackets was proved to be effective in enhancing the strength and deformation capacities of heat-damaged concrete with a square cross-section. The strength growths and the ultimate axial strains of the BFRP-confined heat-damaged square concrete prisms were improved with the increase in the exposure temperature or the number of BFRP jacket layers. Two typical concrete confinement models were then modified by taking the residual mechanical properties of concrete into account to predict the compressive behavior of the BFRP-confined heat-damaged concrete with a square cross-section. The comparisons between the test results and the model predictions are presented, and the accuracy of the concrete confinement models are examined and discussed.
PDF
