The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) emerged in China and rapidly spread worldwide. To prevent SARS-CoV-2 ...dissemination, understanding the in vivo characteristics of SARS-CoV-2 is a high priority. We report a ferret model of SARS-CoV-2 infection and transmission that recapitulates aspects of human disease. SARS-CoV-2-infected ferrets exhibit elevated body temperatures and virus replication. Although fatalities were not observed, SARS-CoV-2-infected ferrets shed virus in nasal washes, saliva, urine, and feces up to 8 days post-infection. At 2 days post-contact, SARS-CoV-2 was detected in all naive direct contact ferrets. Furthermore, a few naive indirect contact ferrets were positive for viral RNA, suggesting airborne transmission. Viral antigens were detected in nasal turbinate, trachea, lungs, and intestine with acute bronchiolitis present in infected lungs. Thus, ferrets represent an infection and transmission animal model of COVID-19 that may facilitate development of SARS-CoV-2 therapeutics and vaccines.
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•SARS-CoV-2-infected ferrets exhibit elevated body temperature and virus replication•SARS-CoV-2 is shed in nasal washes, saliva, urine and feces•SARS-CoV-2 is effectively transmitted to naive ferrets by direct contact•SARS-CoV-2 infection leads acute bronchiolitis in infected ferrets
The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly spreads, leading to a pandemic infection. Kim et al. show that ferrets are highly susceptible to SARS-CoV-2 infection and effectively transmit the virus by direct or indirect contact, recapitulating human infection and transmission.
Core Ideas
We examine SWCC and shear strength under various stress states and suction levels.
Relevant effective stress for granite‐weathered residual soil in Korea is proposed.
We propose a ...numerical framework for strength analysis with transient infiltration.
Potential failure mechanisms of civil infrastructure under rainfall are explored.
We suggest using stress‐dependent SWCC in strength analysis.
This study performed a series of experiments to examine the hydraulic‐mechanical properties of granite‐weathered residual soil in the Korean Peninsula. Particular attention was paid to the soil‐water characteristic curve (SWCC) and shear strength under various stress states and matric suction levels. The experimental results indicated the decisive influence of the stress state on the SWCC, notably in the low range of matric suction. In addition, the evolution of shear strength with suction became significant under high net confining stress. The effective stress using the stress‐independent SWCC could not describe the actual mechanical behaviors of the unsaturated soil. The relevant effective stress for the granite‐weathered residual soil in consideration was then proposed. Next, a numerical framework for strength analysis with infiltration was developed to manifest the practical applications of the experimental results. The analysis results revealed the potential failure mechanisms of the geotechnical infrastructures induced by rainfall. Ignoring the contribution of matric suction may lead to overly conservative outcomes and cannot capture the realistic performance of soil under the rainfall condition. Moreover, the stress‐dependent hydraulic properties are suggested for application in strength analysis for the safer design of geotechnical infrastructure.
A 48 WL stacked 256-Gb V-NAND flash memory with a 3 b MLC technology is presented. Several vertical scale-down effects such as deteriorated WL loading and variations are discussed. To enhance ...performance, reverse read scheme and variable-pulse scheme are presented to cope with nonuniform WL characteristics. For improved performance, dual state machine architecture is proposed to achieve optimal timing for BL and WL, respectively. Also, to maintain robust IO driver strength against PVT variations, an embedded ZQ calibration technique with temperature compensation is introduced. The chip, fabricated in a third generation of V-NAND technology, achieved a density of 2.6 Gb/mm 2 with 53.2 MB/s of program throughput.
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•The potential risk during tunneling with application of a shield TBM is discussed.•The relevant risks were categorized and a fault-tree set was constructed.•Risk analysis was ...performed by adopting FTA and AHP.•The proposed method was reliably validated by comparison with field observation.
In this paper, the potential risk of undesirable events occurring during tunneling with application of a shield tunnel boring machine (TBM) method is discussed along with the risk analysis which can systematically assess overall risk levels. Potential risks and typical scenarios pertaining to shield TBM tunnels have been investigated based on previous case histories and correspondence with experts. The relevant risks from undesirable events were categorized into four groups: cutter-related malfunction, machine blockage or hold-up, mucking problems that hinder transporting excavated materials, and segment defects. A fault-tree set was constructed by grouping risk factors (or causes) into geological, design and construction/management factors. Risk analysis was performed by adopting fault-tree analysis (FTA) and an analytic hierarchy process (AHP) with consideration of the probability and impact of the risks. In addition, the proposed method was reliably validated by comparison with field observation, and thus indicates its applicability to risk management for shield TBM tunneling.
This paper presents a simple numerical framework for infinite slope stability analysis under transient unsaturated seepage conditions. The advantage of the proposed framework, from the practical ...point of view, is to predict the variability in stability of partially saturated slope along with rainfall data. Moreover, the presented framework is adaptable to different types of soil-water characteristic curve (SWCC) models, hydraulic boundary conditions, and heterogeneity in soil properties. A series of stability analyses for hypothetical hillslopes under various conditions was performed to scrutinize the potential failure mechanisms induced by rainfall. The examined factors include the soil texture, rainfall intensity, heterogeneity in soil properties and hydraulic boundary conditions. Also, four widely used SWCC models were applied to assess the influence of this component. The SWCC model was demonstrated to strongly dominate the results of the infinite slope stability analysis under transient unsaturated seepage conditions. For homogeneous hillslopes with a fixed water table, when the rainfall intensity (q) equals the saturated hydraulic conductivity (Ks), slope failure was expected to occur after a short time of rainfall with a relatively shallow slip depth. In contrast, for heterogeneous hillslopes or hillslopes with impermeable bedrock, the failure could take place when q is less than Ks, and the potential failure surface was close to the discontinuity interface or at the bottom of the hillslope. Finally, three case studies of landslides documented in literature were utilized to demonstrate the predictability of the proposed framework in practical applications.
•A framework for infinite slope stability analysis with transient infiltration.•Critical influence of choice of SWCC model on unsaturated slope stability analysis.•Primary factors characterize timing and depth of slope failure.•Exploring the potential failure mechanism of hillslope under various conditions.•Revisiting three case studies of landslides using the proposed framework.
The cement material adopted for a new geothermal well project in South Korea is specialized as the G-class cement, which is commonly used in the oil-well industry, and regulated by the API (American ...Petroleum Institute). In order to maintain the optimal generating performance of geothermal wells, physical properties of the cementing material should be satisfactory. In this paper, the significant material properties (i.e., groutability, uniaxial compressive strength, thermal conductivity, bleeding potential, phenolphthalein indication) of the G-class cement were experimentally examined, with consideration of various water–cement (w/c) ratios as mix proportion. Important findings through the experiments are as follows; (1) Groutability of the G-class cement increases with the addition of a small amount of retarder. (2) There would be a structural problem when the w/c ratio is kept extremely high in order to obtain acceptable groutability. (3) Thermal conductivity of the G-class cement is small enough to prevent heat loss during circulating up hot steam or water from the deep underground to the ground surface. (4) The G-class cement used for geothermal-well cementing causes no bleeding problem. (5) The phenolphthalein indicator is applicable to distinguishing the G-class cement from the drilling mud.
•Groutability of G-class cement increases with addition of a small amount of retarder.•The optimum retarder–cement ratio is recommended between 0.01 and 0.015.•The water–cement ratios of 0.55, 0.6, 0.7, and 0.8 will not cause structural problems.•Thermal conductivity of G-class cement decreases with the water–cement ratio.•The G-class cement for geothermal-well causes no bleeding problem.
The aim of this work is to investigate the effect of ethanol blending to diesel fuel on the combustion and exhaust emission characteristics of a four-cylinder diesel engine with a common-rail ...injection system. The overall spray characteristics, such as the spray tip penetration and the spray cone angle, were studied with respect to the ethanol blending ratio. A spray visualization system and a four-cylinder diesel engine equipped with a combustion and emission analyzer were utilized so as to analyze the spray and exhaust emission characteristics of the ethanol blending diesel fuel. Ethanol blended diesel fuel has a shorter spray tip penetration when compared to pure diesel fuel. In addition, the spray cone angle of ethanol blended fuels is larger. It is believed that the lower fuel density of ethanol blended fuels affects the spray characteristics. When the ethanol blended fuels are injected around top dead center (TDC), they exhibit unstable ignition characteristics because the higher ethanol blending ratio causes a long ignition delay. An advance in the injection timing also induces an increase in the combustion pressure due to the sufficient premixed duration. In a four-cylinder diesel engine, an increase in the ethanol blending ratio leads to a decrease in NO
x emissions due to the high heat of evaporation of ethanol fuel, however, CO and HC emissions increase. In addition, the CO and HC emissions exhibit a decreasing trend according to an increase in the engine load and an advance in the injection timing.
•Six pilot energy textile modules were constructed in the abandoned railroad tunnel testbed.•Long-term field monitoring was performed to evaluate the thermal performance of energy textiles.•The ...slinky type pipe configuration provides the highest thermal performance.•A drainage layer acts as a thermal insulator in energy textiles.
A novel textile-type ground heat exchanger, a so-called “energy textile”, is introduced in this paper. The energy textile to be assembled in a tunnel lining is devised to function as a ground-coupled heat exchanger (GHE) to operate a ground source heat pump (GSHP) system in tunnels. A test bed of six pilot energy textile modules with various configurations was constructed in an abandoned railroad tunnel in South Korea. Long-term field monitoring was performed to measure the heat exchange capacity of each energy textile module by applying artificial heating and cooling loads on it. In the course of monitoring, the inlet and outlet fluid temperatures of the energy textile, the pumping rate, the ground temperature, and the air temperature inside the tunnel were measured continuously. Each type of energy textile modules was compared in terms of its heat exchange efficiency, which appears to be sensitive to fluctuation of air temperature in the tunnel. In addition, three-dimensional computational fluid dynamic (CFD) analyses were carried out, employing FLUENT, to simulate the field test for each energy textile module. After verification of the numerical model with the field measurement, the influence of a drainage layer on the performance of the energy textile was parametrically examined. A conventional design procedure for horizontal GHEs was used in a preliminary design of an energy textile module, taking into consideration the air temperature variation inside the tunnel over the course of one year.
The purpose of this study was to investigate the fuel properties, droplet atomization, combustion performance, and exhaust emission characteristics of gasoline–diesel direct blended fuels in a ...four-cylinder diesel engine. The gasoline fuel was blended as a volumetric fraction of conventional diesel fuel. The droplet size of test fuels was measured using a phase Doppler particle analyzer (PDPA), and the combustion and emission characteristics were investigated for a four-cylinder diesel engine with a common-rail injection system and emission analyzer.
In this study we found that increasing the gasoline volume fraction decreased the fuel density, kinematic viscosity, and surface tension. The temperature for 10% distillation (T10) decreased as the gasoline fraction increased. The blending of gasoline caused a decrease in droplet size by increasing the small droplets and decreasing the large droplets because the surface tension decreased with the addition gasoline fuel, thereby inducing an increase in droplet instability. On the other hand, gasoline blending resulted in an extension of the ignition delay and the formation of a more homogeneous mixture. These combustion characteristics caused the simultaneous reduction of ISNOx and ISsoot. However, the ISHC and ISCO emissions were slightly increased. The difference in ISHC and ISCO emissions between pure diesel and gasoline blended diesel fuels decreased as the engine load increased. An increase in engine load diminished the effects of gasoline blending on combustion performance and exhaust emissions.
► The effect of gasoline blending on combustion and emission were investigated. ► The addition of gasoline induced the decrease of droplet size of blending fuels. ► The extended ignition delay of blended fuels affected the reduction of emissions. ► At low load, HC and CO increased with the gasoline contents. ► Increasing engine load decreased HC and CO emission by gasoline blending.
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•New pillar-reinforcement method was developed to improve pillar stability.•Numerical analysis was carried out to verify the new pillar-reinforcement method.•Small-scale model test ...was also carried out to verify the new method.
To prevent and/or minimize flood-induced damage in metropolitan cities like Seoul, South Korea, construction of an underground rainwater storage cavern becomes an alternative to other conventional countermeasures. In this paper, a new pillar-reinforcement method was developed to improve pillar stability that is crucial for the successful construction of the rainwater storage cavern. Three pillar-reinforcing scenarios were compared numerically: (1) shotcrete installation only, (2) shotcrete installation and pillar-reinforcement with radially pressurized grouting and pre-stress, and (3) shotcrete installation and pillar-reinforcement with vertical upward pressurized grouting and pre-stress. The third pillar-reinforcement readily made the stress condition return to an elastic state showing superior performance to the other methods. In addition, two pillar widths of 800mm and 1200mm were considered to investigate the effects of pillar width on pillar reinforcement by carrying out a small-scale model test, in which the three pillar-reinforcement scenarios can be modeled step-by-step. The pillar width of 1200mm resulted in smaller major principal stresses, representing better reinforcing performance than that of 800mm. Moreover, it was shown that the pressurized grouting enhances the ground strength and more importantly lessened stress concentration in the pillar. However, applying pre-stress further increased ground strength because of the increase in internal pressure.
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