•As of 3 March 2020, COVID-19 has spread rapidly in 46 countries, causing >90 000 confirmed cases and >2946 deaths.•Detection methods for SARS-CoV-2 include RT-qPCR and SHERLOCK technique.•Four ...structural proteins are essential for SARS-CoV-2 assembly and infection, comprising the S, M, E and N proteins.•Pangolin may be a potential intermediate host for SARS-CoV-2.•Antiviral therapy, cellular therapy, immunotherapy and Chinese medicine may be promising therapeutic strategies.
Coronavirus disease 2019 (COVID-19) originated in the city of Wuhan, Hubei Province, Central China, and has spread quickly to 72 countries to date. COVID-19 is caused by a novel coronavirus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) previously provisionally known as 2019 novel coronavirus (2019-nCoV). At present, the newly identified SARS-CoV-2 has caused a large number of deaths with tens of thousands of confirmed cases worldwide, posing a serious threat to public health. However, there are no clinically approved vaccines or specific therapeutic drugs available for COVID-19. Intensive research on the newly emerged SARS-CoV-2 is urgently needed to elucidate the pathogenic mechanisms and epidemiological characteristics and to identify potential drug targets, which will contribute to the development of effective prevention and treatment strategies. Hence, this review will focus on recent progress regarding the structure of SARS-CoV-2 and the characteristics of COVID-19, such as the aetiology, pathogenesis and epidemiological characteristics.
Soil stabilization technology based on microbial-induced carbonate precipitation (MICP) has gained widespread interest in geotechnical engineering. MICP has been found to be able to improve soil ...strength, stiffness, liquefaction resistance, erosion resistance, while maintaining a good permeability simultaneously. MICP processes involves a series of biochemical reactions that are affected by many factors, both intrinsically and externally. This paper reviews various influential factors for MICP process, including bacterial species, concentration of bacteria, temperature, pH, composition and concentration of cementation solution, grouting strategies, and soil properties. Through this comprehensive review, we find that: (1) the species and strains of bacteria, concentration of bacteria solution, temperature, pH value, and the cementation solution properties all affect the characteristics of formed calcium carbonate, such as crystal type, appearance and size, which consequently affect the cementation degree and distribution in geomaterials; (2) the condition with temperature between 20 and 40 °C, pH between 7 and 9.5, the concentration of the cementation solution within 1 mol/L, and high bacteria concentration is optimal for applying MICP in soil. Under the optimal condition, relatively low temperature, high pH value, and low concentration of cementation solution could help retain permeability and vice versa; (3) the effective grain size ranging from 10 to 1000 µm. MICP treatment works most effectively for larger size, well-graded sand; (4) the multi-phase, multi-concentration or electroosmotic grouting method can improve the MICP treatment efficiency. The grouting velocity below 0.042 mol/L/h is beneficial for improving the utilization ratio of cementation solution. The recommended grouting pressure is generally between 0.1 and 0.3 bar for MICP applications in sand and should not exceed 1.1 bar for silty and clayey soils.
Drought‐induced cracking of soils is of great concern with the advent of global climate change. The cracking process accelerates the evaporation rate of pore water, lowers the water retention ...capacity, and degrades the hydraulic‐mechanical properties of soils. Basal friction and layer thickness are two important aspects affecting the subsurface cracking. To explore their detailed effects on soils under drying, we conduct a series of desiccation tests on twelve slurry soil bars and select four types of base materials with different roughness levels and three kinds of layer thicknesses. We track the dynamic cracking process in various samples and adopt the noncontact optical technique—digital image correlation—for the motion of soil particles. Experimental results validate that the coupled effects of basal conditions and soil layer thickness play a key role in governing the soil cracking behavior. The presence of rough bottom surface induces the onset and propagation of desiccation cracks at both top and bottom surfaces. Some of the cracks initiated at the bottom do not propagate through the soil profile. Increasing layer thickness weakens the effect of basal friction on the soil top surface shrinkage but increases the frictional force acting on the base and results in more crack initiations at the bottom. The digital image correlation results further reveal that cracks initiated on the bottom surface and propagated upward vertically are dominated by tensile stresses, while those propagated upward obliquely are dominated by the joint action of shear and tensile stresses.
Key Points
Soil desiccation cracking significantly depends on both basal boundary condition and soil layer thickness
Desiccation cracks initiate not only at soil top surface but also at bottom, which is strongly associated with the basal roughness level
Cracking on top surface is governed by tensile stresses; cracking on bottom surface is governed by coupling of shear and tensile stresses
The purpose of this paper is to review the development and the state of the art in desiccation cracking characterization methods and review the desiccation cracking behaviors of soils. The review ...begins by briefly introducing in Section 1 the influences of desiccation cracking on soil properties and the significance of studying this topic. Section 2 summarizes the past and existing experimental approaches that have been invented and adopted for soil desiccation cracking investigations at both laboratory and field scales. Various theoretical frameworks formulated to account for the underlying cracking mechanisms are presented in Section 3. Section 4 shows the implementation of theoretical frameworks into mesh-based and mesh-free numerical tools to capture the initiation, propagation, and coalescence of desiccation cracks. Section 5 describes the crack dynamics in desiccating soils, with emphases placed on the coupled process of water evaporation, suction increase, and volume shrinkage, and the crack network evolution. Section 6 discusses major influencing factors of soil desiccation cracking covering soil intrinsic properties, boundary constraints, environmental conditions, and soil admixtures. Finally, a brief summary and proposed prospective research works are presented in Sections 7.
A building blocks strategy is an effective approach for constructing the large molecular systems. Herein, we demonstrate that high‐resolution electro‐spray ionization mass spectrometry (HRESI‐MS) ...provides an effective chance to insight the assemble process of the building blocks and guides the construction of high‐nuclearity metal clusters on the basis of the reaction of Ti(OiPr)4, Eu(acac)3, and salicylic acid. The time‐dependent HRESI‐MS indicates that not only a Eu3Ti building block can be formed, but that it can further assemble into a Eu24Ti8 compound. Temperature‐dependent HRESI‐MS reveals that increase of the reaction temperature favors the formation and crystallization of the stable Eu24Ti8 structure. Single‐crystal structural analysis demonstrates that the Eu24Ti8 has a wheel‐like structure with diameter of ca. 4.1 nm and is the highest nuclearity lanthanide‐titanium oxo cluster reported to date.
Wheely big: Under the guidance of the time‐ and temperature‐dependent HRESI‐MS of the reaction, a wheel‐like Eu24Ti8 cluster was synthesized, which is the highest nuclearity lanthanide‐titanium oxo cluster reported to date.
Desiccation cracking is a common natural phenomenon in clayey soils, considerably degrading their mechanical and hydraulic properties. Typical remediation methods are associated with high labor ...costs, high maintenance costs, or the usage of environment-unfriendly chemicals. Microbially induced calcite precipitation (MICP) has emerged as a green and sustainable soil improvement technique. The application of MICP in clayey soils remains poorly investigated due to the presence of microscopic pores among clay soil particles that restrain the free passage of bacteria. In this study, we carry out cyclic wetting-drying tests to characterize the effect of MICP on the desiccation cracking behaviors of clayey soils. We prepare four groups of soil samples sprayed with deionized water, bacteria solution, cementation solution, and both bacteria and cementation solutions, respectively. Soil desiccation cracking behaviors captured by a high-resolution camera are quantified using image processing. We resort to optical microscopy and scanning electron microscopy for microstructural characterizations. Experimental results reveal the effects of fluid type and treatment cycle number on the crack evolution and volumetric deformation of soils. Comparatively, the MICP treatment involving both bacteria and cementation solutions work most effectively in lowering the soil cracking potential. Geometrical parameters featuring the crack pattern such as surface crack ratio, average crack width, total crack length, crack width distribution range and the most probable value of crack width decrease significantly with the increasing treatments. This study is expected to improve the fundamental understanding of desiccation cracking mechanisms in the MICP-treated soils and provide insights into the potential application of MICP for cracking remediation in clayey soils.
•MICP is applicable for the treatment of clayey soils on earth surface.•MICP is effective to increase the desiccation cracking resistance of soil.•Soil surface cracking extent decreases with increasing cycles of MICP treatment.•Precipitated CaCO3 bonds soil particle to improve soil mechanical behavior.
Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease ...represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.
AbstractSurface soil erosion is one of the most common slope degradation processes. In this study, microbial calcification (MC), a stimulated natural biocementation process, was investigated for its ...feasibility as a sandy-slope surface erosion control method. An artificial model slope at 30° was treated by MC via the surface spraying method at three cementation solution concentrations (0.2, 1.0, and 2.0 M). Simulated rainfall was sprayed on the slope surface at 5 mm/min for 30 min. Results show that MC treatment with 0.2- and 1.0-M cementation solution improves surface erosion resistance in terms of observed erosion pattern with time, soil loss weight and rate, and outflow properties. However, MC treatment with 2.0-M cementation solution does not improve surface erosion resistance. Instead, substantial soil loss is observed under rainfall impact while soil is washed away in cemented aggregates. At the end of the rainfall erosion test, microstructural features of the surface samples were identified by scanning electron microscope (SEM) observation. It is found that the effectiveness of MC for sandy-slope surface erosion control is determined by (1) overall CaCO3 precipitation content, (2) treatment depth, and (3) competence between CaCO3 crystal growth and nucleation process.
A classic problem in microbiology is that bacteria display two types of growth behavior when cultured on a mixture of two carbon sources: the two sources are sequentially consumed one after another ...(diauxie) or they are simultaneously consumed (co-utilization). The search for the molecular mechanism of diauxie led to the discovery of the lac operon. However, questions remain as why microbes would bother to have different strategies of taking up nutrients. Here we show that diauxie versus co-utilization can be understood from the topological features of the metabolic network. A model of optimal allocation of protein resources quantitatively explains why and how the cell makes the choice. In case of co-utilization, the model predicts the percentage of each carbon source in supplying the amino acid pools, which is quantitatively verified by experiments. Our work solves a long-standing puzzle and provides a quantitative framework for the carbon source utilization of microbes.
Synthesis and design of a new printed filtering antenna is presented in this communication. For the requirements of efficient integration and simple fabrication, the co-design approach for the ...integration of filter and antenna is introduced. The printed inverted-L antenna and the parallel coupled microstrip line sections are used for example to illustrate the synthesis of a bandpass filtering antenna. The equivalent circuit model for the inverted-L antenna, which is mainly a series RLC circuit, is first established. The values of the corresponding circuit components are then extracted by comparing with the full-wave simulation results. The inverted-L antenna here performs not only a radiator but also the last resonator of the bandpass filter. A design procedure is given, which clearly indicates the steps from the filter specifications to the implementation. As an example, a 2.45 GHz third-order Chebyshev bandpass filter with 0.1 dB equal-ripple response is tackled. Without suffering more circuit area, the proposed structure provides good design accuracy and filter skirt selectivity as compared to the filter simple cascade with antenna and a bandpass filter of the same order. The measured results, including the return loss, total radiated power, and radiation gain versus frequency, agree well with the designed ones.
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