A novel meshless numerical method, called general particle dynamics (GPD), is proposed to simulate samples of rock-like brittle heterogeneous material containing four preexisting flaws under uniaxial ...compressive loads. Numerical simulations are conducted to investigate the initiation, growth, and coalescence of cracks using a GPD code. An elasto-brittle damage model based on an extension of the Hoek–Brown strength criterion is applied to reflect crack initiation, growth, and coalescence and the macrofailure of the rock-like material. The preexisting flaws are simulated by empty particles. The particle is killed when its stresses satisfy the Hoek–Brown strength criterion, and the growth path of cracks is captured through the sequence of such damaged particles. A statistical approach is applied to model the heterogeneity of the rock-like material. It is found from the numerical results that samples containing four preexisting flaws may produce five types of cracks at or near the tips of preexisting flaws including wing, coplanar or quasi-coplanar secondary, oblique secondary, out-of-plane tensile, and out-of-plane shear cracks. Four coalescence modes are observed from the numerical results: tensile (T), compression (C), shear (S), and mixed tension/shear (TS). A higher load is required to induce crack coalescence in the shear mode (S) than the tensile (T) or mixed (TS) mode. It is concluded from the numerical results that crack coalescence occurs following the weakest coalescence path among all possible paths between any two flaws. The numerical results are in good agreement with reported experimental observations.
General particle dynamics (GPD), which is a novel meshless numerical method, is proposed to simulate the initiation, propagation and coalescence of 3D pre-existing penetrating and embedded flaws ...under biaxial compression. The failure process for rock-like materials subjected to biaxial compressive loads is investigated using the numerical code GPD3D. Moreover, internal crack evolution processes are successfully simulated using GPD3D. With increasing lateral stress, the secondary cracks keep growing in the samples, while the growth of the wing cracks is restrained. The samples are mainly split into fragments in a shear failure mode under biaxial compression, which is different from the splitting failure of the samples subjected to uniaxial compression. For specimens with macroscopic pre-existing flaws, the simulated types of cracks, the simulated coalescence types and the simulated failure modes are in good agreement with the experimental results.
Abstract
Background
Recent studies have focused on initial clinical and epidemiological characteristics of the coronavirus disease 2019 (COVID-19), which is the mainly revealing situation in Wuhan, ...Hubei.
Aim
This study aims to reveal more data on the epidemiological and clinical characteristics of COVID-19 patients outside of Wuhan, Zhejiang, China.
Design
This study was a retrospective case series.
Methods
Eighty-eight cases of laboratory-confirmed and three cases of clinically confirmed COVID-19 were admitted to five hospitals in Zhejiang province, China. Data were collected from 20 January 2020 to 11 February 2020.
Results and discussion
Of all 91 patients, 88 (96.70%) were laboratory-confirmed COVID-19 with throat swab samples that tested positive for SARS-Cov-2, three (3.30%) cases were clinically diagnosed. The median age of the patients was 50 (36.5–57) years, and female accounted for 59.34%. In this sample, 40 (43.96%) patients had contracted the disease from local cases, 31 (34.07%) patients had been to Wuhan/Hubei, eight (8.79%) patients had contacted with people from Wuhan, and 11 (12.09%) patients were diagnosed after having flown together in the same flight with no passenger that could later be identified as the source of infection. In particular within the city of Ningbo, 60.52% cases can be traced back to an event held in a temple. The most common symptoms were fever (71.43%), cough (60.44%) and fatigue (43.96%). The median of incubation period was 6 (interquartile range 3–8) days and the median time from the first visit to a doctor to the confirmed diagnosis was 1 (1–2) days. According to the chest computed tomography scans, 67.03% cases had bilateral pneumonia.
Conclusions
Social activity cluster, family cluster and flying alongside with persons already infected with COVID-19 were how people got infected with COVID-19 in Zhejiang.
This paper investigates the African financial development and financial inclusion gaps relative to other peer developing countries. Using a set of variables related to financial development and ...inclusion, we first estimate the gaps between African countries and other developing countries with similar degrees of economic development. Then, we explore the determinants of financial development and inclusion. We find that population density is considerably more important for financial development and inclusion in Africa than elsewhere. Finally, we show evidence that a recent innovation in financial services, mobile banking, has helped to overcome infrastructural problems and improve financial access.
In this paper, the vortex-induced vibrations of a hinged–hinged pipe conveying fluid are examined, by considering the internal fluid velocities ranging from the subcritical to the supercritical ...regions. The nonlinear coupled equations of motion are discretized by employing a four-mode Galerkin method. Based on numerical simulations, diagrams of the displacement amplitude versus the external fluid reduced velocity are constructed for pipes transporting subcritical and supercritical fluid flows. It is shown that when the internal fluid velocity is in the subcritical region, the pipe is always vibrating periodically around the pre-buckling configuration and that with increasing external fluid reduced velocity the peak amplitude of the pipe increases first and then decreases, with jumping phenomenon between the upper and lower response branches. When the internal fluid velocity is in the supercritical region, however, the pipe displays various dynamical behaviors around the post-buckling configuration such as inverse period-doubling bifurcations, periodic and chaotic motions. Moreover, the bifurcation diagrams for vibration amplitude of the pipe with varying internal fluid velocities are constructed for each of the lowest four modes of the pipe in the lock-in conditions. The results show that there is a significant difference between the vibrations of the pipe around the pre-buckling configuration and those around the post-buckling configuration.
Liquid crystalline phases of matter permeate nature and technology, with examples ranging from cell membranes to liquid-crystal displays. Remarkably, electronic liquid-crystal phases can exist in ...two-dimensional electron systems (2DES) at half Landau-level filling in the quantum Hall regime. Theory has predicted the existence of a liquid-crystal smectic phase that breaks both rotational and translational symmetries. However, previous experiments in 2DES are most consistent with an anisotropic nematic phase breaking only rotational symmetry. Here we report three transport phenomena at half-filling in ultra-low disorder 2DES: a non-monotonic temperature dependence of the sample resistance, dramatic onset of large time-dependent resistance fluctuations, and a sharp feature in the differential resistance suggestive of depinning. These data suggest that a sequence of symmetry-breaking phase transitions occurs as temperature is lowered: first a transition from an isotropic liquid to a nematic phase and finally to a liquid-crystal smectic phase.
We study rating shopping on the MBS market. Outside of AAA, losses are higher on singlerated tranches than on multi-rated ones, and yields predict future losses for single-rated tranches, but not for ...multi-rated ones. Conversely, ratings have less explanatory power for single-rated tranches. These results suggest that single-rated tranches have been "shopped," whereby pessimistic ratings never reach the market. For AAA-rated MBS, by contrast, 93% receive two or three such ratings, and those ratings agree 97% of the time. This ratings convergence suggests that agencies "cater" to investors, who cannot purchase a tranche unless it has multiple AAA ratings.
Single-ended travelling wave fault location methods have the advantages of avoiding the complexities and costs of the remote-end synchronisation. However, the determination of the arrival time of the ...travelling wave and its corresponding propagation velocity is a difficult problem which is apt to limit the algorithms' accuracy. A novel single-ended fault location method based on travelling wave time-frequency characteristics for transmission lines is proposed in this study. The time-frequency characteristics of the travelling wave signal are described by the Lipschitz exponent. The Lipschitz exponent of the second transient wave-front signal is estimated by using the wavelet transform and the least square method. Extensive simulations have been carried out in PSCAD/EMTDC, and the results demonstrate that the accuracy of the proposed fault location method is significantly improved comparing with that of the traditional travelling wave fault location method. The proposed method is insensitive to different fault conditions, and it adapts to both transposed and untransposed lines well.
A novel meshless numerical method, known as general particle dynamics (GPD3D), is proposed to simulate the failure process of slopes as well as the failure process of 2D and 3D samples. An ...elasto-brittle damage model based on the Mohr–Coulomb criterion is applied to investigate the initiation, growth and coalescence of cracks as well as the macro-failure of slopes. The Weibull statistical approach is applied to model the heterogeneity of geomaterials. Five macro-fracture modes of samples subjected to uniaxial compressive loads are modeled due to the heterogeneity of geomaterials. The safety factor and slip surface of the slope are determined by using the GPD3D approach. The numerical results from the GPD approach are in good agreement with those from the limit equilibrium method and FEM. The present numerical method is demonstrated to predict the complex fracture processes of slopes.
•General particle dynamics is proposed.•The Weibull statistical method is used to model the heterogeneity of geomaterials.•The safety factor and slip surface of the slope are determined.•The initiation, growth and coalescence of cracks are simulated.
The vortex-induced vibrations of a long flexible pipe conveying fluctuating flows are investigated via a two-mode discretization of the governing differential equations. In the present work, the ...internal fluid velocity is assumed to have a harmonically varying component superposed on a steady mean velocity. Direct perturbation method of multiple scales (MMS) is adopted to transform the governing nonlinear partial differential equations (PDEs) into ordinary differential equations (ODEs), which are then analyzed numerically for the pipe with principal parametric resonances during lock-in for each of the first two modes. The results indicate that in the case of a pipe containing fluctuating flows, the peak of vibration amplitudes is larger than that of a pipe conveying steady flows. With the increase of detuning parameter for the frequency of pulsating flow, the variation range of vibration amplitudes of the pipe enlarges first and then narrows, with jumping phenomenon that the vibration amplitude changes from multi-value to single-value and then returns to multi-value between the two regions of multi-value responses, which has not been discovered yet. From the amplitude-frequency response curves one can see that the hysteresis may occur with small increments or decrements of the detuning parameter. It is also found that if the pipe system is in the lock-in condition for a certain mode, the pulsating component can have an obvious impact on the dynamics of the pipe only when the parametric resonance occurs in the same mode. In addition, the method of numerical simulations (MNS) is directly employed to verify our implementation of MMS.
•Vortex-induced vibrations of a pipe conveying fluctuating flows are analyzed.•Effect of internal pulsating fluid flow on the dynamics is found to be pronounced.•The system displays both multi-value and single-value responses.•Hysteresis may occur with small increment or decrement of the detuning parameter.
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