Quercetin is a bioactive compound that is widely used in botanical medicine and traditional Chinese medicine due to its potent antioxidant activity. In recent years, antioxidant activities of ...quercetin have been studied extensively, including its effects on glutathione (GSH), enzymatic activity, signal transduction pathways, and reactive oxygen species (ROS) caused by environmental and toxicological factors. Chemical studies on quercetin have mainly focused on the antioxidant activity of its metal ion complexes and complex ions. In this review, we highlight the recent advances in the antioxidant activities, chemical research, and medicinal application of quercetin.
This study tightly integrates complementary spectral and spatial features for deep learning based multi-channel speaker separation in reverberant environments. The key idea is to localize individual ...speakers so that an enhancement network can be trained on spatial as well as spectral features to extract the speaker from an estimated direction and with specific spectral structures. The spatial and spectral features are designed in a way such that the trained models are blind to the number of microphones and microphone geometry. To determine the direction of the speaker of interest, we identify time-frequency (T-F) units dominated by that speaker and only use them for direction estimation. The T-F unit level speaker dominance is determined by a two-channel chimera++ network, which combines deep clustering and permutation invariant training at the objective function level, and integrates spectral and interchannel phase patterns at the input feature level. In addition, T-F masking based beamforming is tightly integrated in the system by leveraging the magnitudes and phases produced by beamforming. Strong separation performance has been observed on reverberant talker-independent speaker separation, which separates reverberant speaker mixtures based on a random number of microphones arranged in arbitrary linear-array geometry.
•Flow and temperature at high temperature cannot be fully-developed.•Non-dimensional velocity and temperature are proposed to evaluate performances.•Local Nusselt number and friction factor at high ...and low temperature are similar.•Bigger inclined angle should be used in cold region when using hybrid channels.•Optimal inclined angles are depended on operating conditions.
High temperature heat exchanger is one of the most important components to transfer heat from the first loop to the second loop in the very high temperature reactor in nuclear energy application. In order to enhance the heat transfer performance, a mini-channel heat exchanger called printed circuit heat exchanger has attracted more attention in recent years. In this paper, the thermal–hydraulic performance of zigzag-type printed circuit heat exchanger with helium as the working fluid operating at the typical temperature of 900°C in the very high temperature reactor is studied. It is found that the flow and temperature at high temperature cannot achieve a fully-developed condition due to the significant variation of thermal physical properties arisen from the large temperature difference. However, the non-dimensional velocity and temperature can become steady after the second pitch and is similar to the fluid flow behaviors at low temperature. Therefore the local Nusselt number and friction factor at high temperature can match well with those at low temperature when the Reynolds number is bigger than 900. With the increase of inclined angle, the heat transfer and pressure drop increase. It is recommended to put the channel with a larger inclined angle to the cold region when using the hybrid channels. The heat transfer enhancement method with inclined angles completely depends on the operating conditions.
This study proposes a complex spectral mapping approach for single- and multi-channel speech enhancement, where deep neural networks (DNNs) are used to predict the real and imaginary (RI) components ...of the direct-path signal from noisy and reverberant ones. The proposed system contains two DNNs. The first one performs single-channel complex spectral mapping. The estimated complex spectra are used to compute a minimum variance distortion-less response (MVDR) beamformer. The RI components of beamforming results, which encode spatial information, are then combined with the RI components of the mixture to train the second DNN for multi-channel complex spectral mapping. With estimated complex spectra, we also propose a novel method of time-varying beamforming. State-of-the-Art performance is obtained on the speech enhancement and recognition tasks of the CHiME-4 corpus. More specifically, our system obtains 6.82%, 3.19% and 1.99% word error rates (WER) respectively on the single-, two-, and six-microphone tasks of CHiME-4, significantly surpassing the current best results of 9.15%, 3.91% and 2.24% WER.
•The printed circuit heat exchanger (PCHE) is tested in supercritical CO2 system.•The thermal performances of CO2 in transcritical and supercritical states are tested.•The correlations of CO2 ...operating in PCHE with straight channels are fitted.
The supercritical CO2 Brayton cycle (SCO2-BC) is proposed to be used as the concept of fast cooled reactor (FCR), which is a typical application in the 4th generation reactors. The recuperator and cooler, which acted as important components in SCO2-BC, are required for long-term operation especially at the high pressure condition. However, the traditional shell-and-tube heat exchanger, which already has mature fabrication technology, is not appropriate in the developing miniaturized thermal system because of its low compactness. In the present paper, the compact printed circuit heat exchanger (PCHE) with straight ribs is manufactured by the photochemical etching technology and the diffusion bonding method independently. Then, the thermohydraulic performance of PCHE is tested on the SCO2-water experiment platform. Considering the difference of thermal properties of working fluid, the comparison of thermal and hydraulic performance between SCO2 and water in the tested PCHE is studied at the same mass flow rate, which shows that the SCO2 has better heat transfer capability than water fluid. Further, the heat transfer rate and pressure loss of PCHE are investigated at different SCO2 operating pressure, which indicates that the PCHE has better comprehensive performance when it operates at higher pressure condition. Meanwhile, the extreme operating condition due to the pseudo-critical point of CO2 working in the PCHE is analyzed comparing with the normal operating condition. The results show that the comprehensive performance of PCHE is significantly reduced nearly 17.6% when operates at the transcritical state. The heat transfer correlation of PCHE with straight ribs is fitted by experimental data in both the supercritical and transcritical states in order to simplifying design process.
A copper-catalyzed aminoazidation of unactivated alkenes is achieved for the synthesis of versatile unsymmetrical 1,2-diamine derivatives. This transformation offers an effective approach to ...installing an amide and an azide from two diffenent amino precursors onto both terminal and internal alkenes, with remarkable regio- and stereoselectivity. Mechanistic studies show that this diamination reaction proceeds via a nucleophilic amino cyclization followed by an intermolecular C-N bond formation using electrophilic azidoiodinane. This pathway differs from previous azidoiodinane-initiated alkene functionalization, suggesting new reactivity of azidoiodinane. Furthermore, this aminoazidation reaction provides an efficient strategy to introduce azide, one of the most useful chemical reporters, onto a broad range of bioactive azaheterocycles, offering new opportunities in bioorthogonal chemistry and biological studies. Rapid syntheses of 5-HT
agonist, (-)-enduracididine and azido-cholesterol derivatives demonstrate broad applications of this method in organic synthesis, medicinal chemistry, and chemical biology.
The improvement of heat recovery in the industry has traditionally been approached from two different viewpoints – Process Intensification and Process Integration. Many of the developments took the ...form of Heat Transfer Enhancement or Heat Integration within Heat Exchanger Networks, developing in parallel. In the past decade, however, there have been successful applications of both approaches together, resulting in cost benefits for heat-integrated retrofits. Heat Integration literature has continued to provide a variety of network modelling and retrofit approaches. Recent reviews of the area show that the mathematical-based and thermodynamic-based approaches have reached maturity within the current modelling paradigm. There are indications that the modelling concepts and frameworks need a further step-change to bridge the gap between the solutions to heat recovery problems offered by the current methods and the practical implementation in terms of real retrofit actions, leading to economically feasible reduction of energy use and emissions. The current paper takes these indications as a departure point and reviews the history and the recent developments in the areas of Heat Transfer Enhancement and the retrofit of Heat Exchanger Networks, providing a critical analysis from the viewpoint of obtaining practical solutions with positive cash flows, while minimising the issues related to operability – emissions, flexible operation and control. The analysis clearly shows the need to focus future research and development efforts on increasing model fidelity and practicality, addressing operability issues, and most importantly – development of flexible and efficient tools for communicating optimisation results to industrial practitioners and plant managers who would implement the process retrofit recommendations.
•Combining Heat Transfer Enhancement and Heat Integration is highly beneficial.•Mathematical Programming and thermodynamic retrofit approaches have reached maturity.•Solutions for improving Waste Heat Utilisation in the industry need to be more practical.•Research objectives should refocus on maximising Life Cycle asset performance.•There is an ongoing need to extend the software tools to further support for energy retrofit.
The contents of ten heavy metals (Cr, Hg, As, Pb, Ni, Cd, Ti, Cu, Zn and V) in 413 topsoil samples from Puning City, Guangdong Province, China were investigated. Obvious enrichment of Hg, As, Pb, Cd ...and Zn were presented, and the contents of Hg and As in 5.8% and 3.4% samples respectively were higher than the guideline values recommended by the Chinese Environmental Quality Standard for Soils. Chromium and V were presented no enrichment and no pollution. According to one-way analysis of variance, the mean contents of Hg, Pb, Cu and Zn in land for construction were significantly higher than farmland and natural vegetation, but the land use had no obvious effect on other heavy metals. Furthermore, the potential sources of ten heavy metals were identified and apportioned in combination with geostatistics, correlation analysis and positive matrix factorization model. The results were following as: a) Pb, Zn and Cu mainly origin from vehicle emission and atmosphere deposition, and the hotspots approximately distributed in the areas of intensive traffic and near main roads; b) Hg and Cd were derived to industrial activities related to pharmaceutical industries, the textile and dyeing industries and e-waste recycling industries, and high-value areas were mainly concentrated in the northeast of the urban area where the industrial parks have been distributed; c) Soil parent material (Jurassic shale) was the main source of Cr, Ni, V and Ti; d) As mainly came from agricultural inputs such as pesticides or herbicides, livestock and fertilizers. Meanwhile, the contributions of four sources were 33.08%, 24.04%, 27.11% and 15.77% of the total contribution, respectively.
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•Obvious enrichment of Hg, Cd, Pb and Zn were found in Puning soils.•Four sources of soil heavy metals were apportioned by geostatistics and PMF.•Vehicle emission and industrial activities were the main anthropogenic source.
As reported by the World Health Organization, a novel coronavirus (2019-nCoV) was identified as the causative virus of Wuhan pneumonia of unknown etiology by Chinese authorities on 7 January, 2020. ...The virus was named as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by International Committee on Taxonomy of Viruses on 11 February, 2020. This study aimed to develop a mathematical model for calculating the transmissibility of the virus.
In this study, we developed a Bats-Hosts-Reservoir-People transmission network model for simulating the potential transmission from the infection source (probably be bats) to the human infection. Since the Bats-Hosts-Reservoir network was hard to explore clearly and public concerns were focusing on the transmission from Huanan Seafood Wholesale Market (reservoir) to people, we simplified the model as Reservoir-People (RP) transmission network model. The next generation matrix approach was adopted to calculate the basic reproduction number (R
) from the RP model to assess the transmissibility of the SARS-CoV-2.
The value of R
was estimated of 2.30 from reservoir to person and 3.58 from person to person which means that the expected number of secondary infections that result from introducing a single infected individual into an otherwise susceptible population was 3.58.
Our model showed that the transmissibility of SARS-CoV-2 was higher than the Middle East respiratory syndrome in the Middle East countries, similar to severe acute respiratory syndrome, but lower than MERS in the Republic of Korea.
Deep neural network (DNN) based end-to-end optimization in the complex time-frequency (T-F) domain or time domain has shown considerable potential in monaural speech separation. Many recent studies ...optimize loss functions defined solely in the time or complex domain, without including a loss on magnitude. Although such loss functions typically produce better scores if the evaluation metrics are objective time-domain metrics, they however produce worse scores on speech quality and intelligibility metrics and usually lead to worse speech recognition performance, compared with including a loss on magnitude. While this phenomenon has been experimentally observed by many studies, it is often not accurately explained and there lacks a thorough understanding on its fundamental cause. This letter provides a novel view from the perspective of the implicit compensation between estimated magnitude and phase. Analytical results based on monaural speech separation and robust automatic speech recognition (ASR) tasks in noisy-reverberant conditions support the validity of our view.
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