비만아 부모의 돌봄 경험: q 방법론

By 27 February 2020, the outbreak of coronavirus disease 2019 (COVID-19) caused 82 623 confirmed cases and 2858 deaths globally, more than severe acute respiratory syndrome (SARS) (8273 cases, 775 deaths) and Middle East respiratory syndrome (MERS) (1139 cases, 431 deaths) caused in 2003 and 2013, respectively. COVID-19 has spread to 46 countries internationally. Total fatality rate of COVID-19 is estimated at 3.46% by far based on published data from the Chinese Center for Disease Control and Prevention (China CDC). Average incubation period of COVID-19 is around 6.4 days, ranges from 0 to 24 days. The basic reproductive number (R0 ) of COVID-19 ranges from 2 to 3.5 at the early phase regardless of different prediction models, which is higher than SARS and MERS. A study from China CDC showed majority of patients (80.9%) were considered asymptomatic or mild pneumonia but released large amounts of viruses at the early phase of infection, which posed enormous challenges for containing the spread of COVID-19. Nosocomial transmission was another severe problem. A total of 3019 health workers were infected by 12 February 2020, which accounted for 3.83% of total number of infections, and extremely burdened the health system, especially in Wuhan. Limited epidemiological and clinical data suggest that the disease spectrum of COVID-19 may differ from SARS or MERS. We summarize latest literatures on genetic, epidemiological, and clinical features of COVID-19 in comparison to SARS and MERS and emphasize special measures on diagnosis and potential interventions. This review will improve our understanding of the unique features of COVID-19 and enhance our control measures in the future.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/jmv.25748

Unique epidemiological and clinical features of the emerging 2019 novel coronavirus pneumonia (COVID-19) implicate special control measures.

A review of techniques, advances and outstanding issues in numerical modelling for rock mechanics and rock engineering

The Mohr–Coulomb (M–C) fracture criterion is revisited with an objective of describing ductile fracture of isotropic crack-free solids. This criterion has been extensively used in rock and soil mechanics as it correctly accounts for the effects of hydrostatic pressure as well as the Lode angle parameter. It turns out that these two parameters, which are critical for characterizing fracture of geo-materials, also control fracture of ductile metals (Bai and Wierzbicki 2008; Xue 2007; Barsoum 2006; Wilkins et al. 1980). The local form of the M–C criterion is transformed/extended to the spherical coordinate system, where the axes are the equivalent strain to fracture $${\bar \varepsilon_f}$$
 , the stress triaxiality η, and the normalized Lode angle parameter $${\bar \theta}$$
 . For a proportional loading, the fracture surface is shown to be an asymmetric function of $${\bar \theta}$$
 . A detailed parametric study is performed to demonstrate the effect of model parameters on the fracture locus. It was found that the M–C fracture locus predicts almost exactly the exponential decay of the material ductility with stress triaxiality, which is in accord with theoretical analysis of Rice and Tracey (1969) and the empirical equation of Hancock and Mackenzie (1976), Johnson and Cook (1985). The M–C criterion also predicts a form of Lode angle dependence which is close to parabolic. Test results of two materials, 2024-T351 aluminum alloy and TRIP RA-K40/70 (TRIP690) high strength steel sheets, are used to calibrate and validate the proposed M–C fracture model. Another advantage of the M–C fracture model is that it predicts uniquely the orientation of the fracture surface. It is shown that the direction cosines of the unit normal vector to the fracture surface are functions of the “friction” coefficient in the M–C criterion. The phenomenological and physical sound M–C criterion has a great potential to be used as an engineering tool for predicting ductile fracture.

Application of extended Mohr–Coulomb criterion to ductile fracture

The purpose of this review is to discuss the development and the state of the art in dynamic testing techniques and dynamic mechanical behaviour of rock materials. The review begins by briefly introducing the history of rock dynamics and explaining the significance of studying these issues. Loading techniques commonly used for both intermediate and high strain rate tests and measurement techniques for dynamic stress and deformation are critically assessed in Sects. 2 and 3. In Sect. 4, methods of dynamic testing and estimation to obtain stress–strain curves at high strain rate are summarized, followed by an in-depth description of various dynamic mechanical properties (e.g. uniaxial and triaxial compressive strength, tensile strength, shear strength and fracture toughness) and corresponding fracture behaviour. Some influencing rock structural features (i.e. microstructure, size and shape) and testing conditions (i.e. confining pressure, temperature and water saturation) are considered, ending with some popular semi-empirical rate-dependent equations for the enhancement of dynamic mechanical properties. Section 5 discusses physical mechanisms of strain rate effects. Section 6 describes phenomenological and mechanically based rate-dependent constitutive models established from the knowledge of the stress–strain behaviour and physical mechanisms. Section 7 presents dynamic fracture criteria for quasi-brittle materials. Finally, a brief summary and some aspects of prospective research are presented.

/pdf/a-review-of-dynamic-experimental-techniques-and-mechanical-2kstp2wfg4.pdf

A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials

Dynamic propagation behavior of mode I crack in MSF/PVA-MKPC NSCB specimens after high-temperature exposure

The K-type joint, which consists of the web members and the chord members with varied angles welded together, has been widely adopted in long-span steel truss bridges. However, its fatigue performance has been rarely considered, despite its critical role in bridge structural safety and durability. Accordingly, the FE model of the K-type joint was established in Abaqus and the fatigue performance analysis was conducted, in which the effect of web/chord thickness ratio (τ), chord/web angle (θ), and chord with rib stiffener were investigated. Take the Mingzhu Bay steel truss arch bridge as an engineering background, the hot spot stress method was employed to calculate the fatigue performance of three K-type joints in unfavorable locations. Furthermore, a 3D full-scall bridge model was built to evaluate the fatigue performance of the K-type joints under standard and overloaded moving vehicle load scenarios. The results show that the max hot spot stress factor (SCFmax) of the web and chord member is influenced by τ and θ. The chord members added stiffener is founded to be an effective way to enhance fatigue performance. The fatigue stress intensities of the three unfavorable locations meet the Eurocode 3 specification requirements, but the one in the mid-truss arch is not satisfied under an overloaded vehicle loading rate of 25%.

/pdf/fatigue-performance-evaluation-of-k-type-joints-in-long-span-3aec9epz.pdf

Fatigue Performance Evaluation of K-Type Joints in Long-Span Steel Truss Arch Bridge

Cloud condensation nuclei (CCN) is a critical parameter for simulating aerosol‐cloud interaction and aerosol indirect effects. Here we characterize the vertical differences of CCN number concentration (NCCN) between ground level and 260 m based on field measurements on a meteorological tower in Beijing. The observed ground aerosol number concentration was about 16% higher than 260 m, unexpectedly, the ground NCCN was on average 20% lower than 260 m within the atmospheric typical supersaturation (S) range of 0.1%–0.4%. Using positive matrix factorization analysis, we clarified that the higher NCCN at 260 m was primarily due to increased contributions from both regional transport and secondary processes. The aerosol particles from the regional transport contributed 20%–50% and 31%–57% of CCN respectively at ground and 260 m within typical S, with higher proportions at smaller S. The secondary processes contributed generally about the equal amount CCN between ground (42%–55%) and 260 m (37%–52%). The total contribution of regional transport and secondary processes, as the main sources, contributed 72%–94% CCN during the campaign. While, nucleation events and local primary sources accounted for the smallest proportion of NCCN at both heights. Under polluted conditions, the vertical difference was further enlarged. The results suggest that surface observations under clean conditions may well represent cloud nuclei aloft. However, the NCCN measured at ground may be unexpectedly much lower than the tower height in polluted conditions, likely leading to an underestimation on cloud nuclei aloft during the field campaign.

Jian Zhao

Papers

Dynamic propagation behavior of mode I crack in MSF/PVA-MKPC NSCB specimens after high-temperature exposure

Fatigue Performance Evaluation of K-Type Joints in Long-Span Steel Truss Arch Bridge

Source Apportionment of Cloud Nuclei at 260 m and Ground Level in Urban Beijing