Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is pandemic. Prevention and control strategies require an improved understanding of SARS-CoV-2 dynamics. We did a rapid review of the ...literature on SARS-CoV-2 viral dynamics with a focus on infective dose. We sought comparisons of SARS-CoV-2 with other respiratory viruses including SARS-CoV-1 and Middle East respiratory syndrome coronavirus. We examined laboratory animal and human studies. The literature on infective dose, transmission and routes of exposure was limited specially in humans, and varying endpoints were used for measurement of infection. Despite variability in animal studies, there was some evidence that increased dose at exposure correlated with higher viral load clinically, and severe symptoms. Higher viral load measures did not reflect coronavirus disease 2019 severity. Aerosol transmission seemed to raise the risk of more severe respiratory complications in animals. An accurate quantitative estimate of the infective dose of SARS-CoV-2 in humans is not currently feasible and needs further research. Our review suggests that it is small, perhaps about 100 particles. Further work is also required on the relationship between routes of transmission, infective dose, co-infection and outcomes.
•COVID-19 is transmitted from asymptomatic individuals to susceptible individuals.•COVID-19 is transmitted from symptomatic individuals to susceptible individuals.•Since R0=1.6 is greater than 1, the ...COVID-19 will spread exponentially.•If COVID-19 is not controlled, it is estimated that about 20 million people will become infected in the next three years.
We present a mathematical model for the transmission of COVID-19 by the Caputo fractional-order derivative. We calculate the equilibrium points and the reproduction number for the model and obtain the region of the feasibility of system. By fixed point theory, we prove the existence of a unique solution. Using the generalized Adams-Bashforth-Moulton method, we solve the system and obtain the approximate solutions. We present a numerical simulation for the transmission of COVID-19 in the world, and in this simulation, the reproduction number is obtained as R0=1:610007996, which shows that the epidemic continues.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
As an alluring metal-free polymeric semiconductor material, graphite-like carbon nitride (g-C
3
N
4
; abbreviated as GCN) has triggered a new impetus in the field of photocatalysis, mainly favoured ...from its fascinating physicochemical and photoelectronic structural features. However, certain inherent drawbacks, involving rapid reassembly of photocarriers, low specific surface area and insufficient optical absorption, limit the wide-range applicability of GCN. Generation of 0D point defects mainly by introducing vacancies (C and/or N) into the framework of GCN has spurred extensive consideration owing to their distinctive qualities to manoeuvre substantially, the optical absorption, radiative carrier isolation, and surface photoreactions. The present review endeavours to summarise a comprehensive study on vacancy defect engineered GCN. Starting from the basic introduction of defects and C/N vacancy modulated GCN, numerous advanced strategies for the controlled designing of vacancy rich GCN have been explored and discussed. Afterwards, light was thrown on the various substantial technologies which are useful for characterising and identifying the introduction of defects in GCN. The salient significance of defect engineering in GCN has been reviewed concerning its impact on optical absorption, charge isolation and surface photoreaction ability. Typically, the achievement of defect engineered GCN has been scrutinised toward various applications like photocatalytic water splitting, CO
2
conversion, N
2
fixation, pollutant degradation, and H
2
O
2
production. Finally, the review ends with conclusions and vouchsafing future challenges and opportunities on the intriguing and emerging area of vacancy defect engineered GCN photocatalysts.
As an alluring metal-free polymeric semiconductor material, graphite-like carbon nitride (g-C
3
N
4
; abbreviated as GCN) has triggered a new impetus in the field of photocatalysis, mainly favoured from its fascinating physicochemical and photoelectronic structural features.
Unlike quantum dots, photophysical properties of carbon dots (CDs) are not strongly correlated with particle size. The origin of CD photoluminescence has been related to sp2 domain size and the ...abundance of oxidized surface defects. However, direct imaging of surface-accessible spatially localized oxidized defects is still lacking. In this work, solvothermal-synthesized CDs are fractionated into different colors by polarity-based chromatography. We then study the mechanism of CD fluorescence by directly imaging individual CDs with subparticle resolution by scanning tunneling microscopy. Density of states imaging of CDs reveals that the graphitic core has a large bandgap that is inconsistent with observed fluorescence wavelength, whereas localized defects have smaller electronic gaps for both red-emitting dots (rCDs) and blue-emitting dots (bCDs). For individual bCDs within our laser tuning range, we directly image optically active surface defects (ca. 1–3 nm in size) and their bandgaps, which agree with the emission wavelength of the ensemble from which the bCDs were taken. We find that the emissive defects are not necessarily the ones with the smallest gap, consistent with quantum yields less than unity (0.1–0.26). X-ray photoelectron spectroscopy and pH-dependent fluorescence titration show that oxygen-containing surface-accessible protonatable functional groups (e.g., phenolic −OH, −COOH) define the chemical identity of the defects. This observation explains why we detect neither long-lived optical excitation of the core nor a correlation between size and emission wavelength. Instead, control over the number of oxygen-containing defects defines the emission wavelength, with more oxidized defects at the surface producing redder emission wavelengths.
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IJS, KILJ, NUK, PNG, UL, UM
Since it was first discovered, thousands of years ago, silkworm silk has been known to be an abundant biopolymer with a vast range of attractive properties. The utilization of silk fibroin (SF), the ...main protein of silkworm silk, has not been limited to the textile industry but has been further extended to various high-tech application areas, including biomaterials for drug delivery systems and tissue engineering. The outstanding mechanical properties of SF, including its facile processability, superior biocompatibility, controllable biodegradation, and versatile functionalization have allowed its use for innovative applications. In this review, we describe the structure, composition, general properties, and structure-properties relationship of SF. In addition, the methods used for the fabrication and modification of various materials are briefly addressed. Lastly, recent applications of SF-based materials for small molecule drug delivery, biological drug delivery, gene therapy, wound healing, and bone regeneration are reviewed and our perspectives on future development of these favorable materials are also shared.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Designing Doherty power amplifiers (PAs) at high millimeter-wave (mm-Wave) range remains a major challenge because most Doherty combiners at this frequency band are inefficient. To resolve this ...bottleneck, we analyze balun response under load variation and subsequently propose the Doherty PA architecture with impedance inverting and scaling baluns that perform active load modulation on differential PAs and delivers combined power to a single-ended load. At the PA output/input stage, instead of utilizing the transformer-based balun commonly used at RF and low mm-Wave frequencies, we explore the coupler-based balun to resonate out the device parasitic capacitance and achieve well-balanced differential to single-ended conversion at high mm-Wave frequencies. Based on the coupled-line theory and our analysis, we derive the Y matrix of the coupler-based balun and originate various solutions for baluns that can invert or scale impedance. From this derivation, we conceive a canonical form of impedance inverting baluns when the electrical length of coupled lines equals 45°. We also propose a close-formed solution for the coupler-based impedance scaling balun that is electrically equivalent to an idealistic transformer in series with a small inductance. We then combine the proposed impedance inverting and scaling balun structures to construct a Doherty network that exhibits desirable Doherty active load modulation and occupies a single-transformer footprint. On the active circuit design, we employ the adaptive biasing circuit for both driver and PA stages of the auxiliary PA to enhance the main and auxiliary cooperation. Using a 45-nm GlobalFoundries CMOS SOI process, we fabricate a proof-of-concept Doherty PA that demonstrates 20.1-dBm P sat , 19.3dBm OP 1,dB , 26% peak power-added efficiency (PAE), and 16.6% PAE at 7-dB power back-off (PBO) from OP 1 dB at 60 GHz. Our results indicate a substantial PAE enhancement at PBO and a state-of-the-art modulation efficiency achieved when transmitting digital pre-distortion (DPD)-free 64-QAM-modulated signals.
Solar radiation is a sustainable, unlimited source of energy for electricity and chemical reactions, yet the conversion efficiency of actual processes is limited and controlled by photocarriers ...migration and separation. Enhancing the conversion efficiency would require to suppress the recombination of photogenerated electron–hole pairs and improve the low redox potentials. This can be done during the growth of step-scheme (S-scheme) heterojunctions. Here we review the charge transfer of S-scheme heterojunctions involving a reduction and oxidation photocatalyst in staggered band arrangement with Fermi level differences. We present factors determining the validation of the S-scheme mechanism with respective characterization techniques, including in situ and ex situ experiments, and theoretical studies. We show mechanistic drawbacks of traditional photocatalytic systems to highlight the advantages of S-scheme photocatalysts. We describe co-catalyst loading, bandgap tuning, and interfacial optimization that ultimately achieve highly efficient photocatalysis. Last, application for water splitting, CO
2
conversion, pollutant degradation, bacterial inactivation and others is discussed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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