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Macroscopic mechanical properties of granular materials are closely related to particle morphology. For practical reasons, the morphological features are commonly examined from projected two-dimensional (2D) images of the three-dimensional (3D) particles. This brings forward the need for quantifying the correlations between the 2D and 3D particle descriptors. This paper addresses these correlations for irregular granular particles. Three-dimensional images of sand particles were acquired through microfocus X-ray computed tomography, based on which 3D surfaces of the particles were reconstructed using spherical harmonic analyses. The 3D particle size and shape descriptors were subsequently evaluated. All-around projection and random projection of the particles onto 2D planes were undertaken numerically to obtain the projected 2D images and thus the corresponding 2D size and shape descriptors. The results indicate that there are close correlations between 3D and 2D size descriptors averaged from the all-around projections. 2D and 3D shape descriptors can be approximately fitted with a linear relationship. The mean value of 2D descriptors of the tested sands obtained from a series of independent random-projection tests is essentially identical to that from the all-around projections; except that the data from the random-projection tests show a larger scatter. In light of the relationships among the descriptors, a novel and promising approach to predict the cumulative distribution of 3D descriptors from that of 2D descriptors evaluated from a random-projection test is proposed.

Fast radio bursts (FRBs) are millisecond-duration radio transients 1 , 2 of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star magnetospheres 3 – 5 or relativistic shocks far from the central energy source 6 – 8 . Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters 9 , 10 or variable polarization angles in some other apparently one-off events 11 , 12 . Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks. Polarization observations of the fast radio burst FRB 180301 with the FAST radio telescope show diverse polarization angle swings, consistent with a magnetospheric origin of the emission.

This paper presents a thermodynamically consistent constitutive model for natural soils with bonds. In the model, the free energy (the internal energy available to do work) is contributed partly by the so-called frozen or locked energy, whose evolution is assumed to be homogeneously related to the irrecoverable deformation. During loading, the bonds existing in the natural soil not only boost the dissipation rate but also liberate certain historically accumulated locked energy. Such effects, however, are diminished as loading proceeds and the bonds are destroyed. The novel aspect of the present model is that it accommodates both the Mohr–Coulomb and critical-state failure modes, and the two modes are unified through the evolution law of a thermodynamic force associated with the locked bonding energy. As compared with the classical Cam-clay models, the model contains two additional material constants, where one is proposed by Collins & Kelly to improve the shape of the yield surface, and the other is dedicated to bonding evolution. The calibration procedure for the material parameters is provided. The capability of the model is demonstrated by a series of model simulations on a hypothetical bonded soil under various triaxial loading paths, and the model response is also compared with representative testing results in the literature.

Background On 21 February 2005 the Leuwigajah dumpsite, Bandung (Java, Indonesia) was affected by a large slide after heavy rainfalls. Second deadliest waste slide in history, it buried 71 houses and killed 143 people. Amongst the contemporary disastrous events of this type, only a few have been documented. We explored failure preconditions, triggering mechanisms and local context that conducted to this disaster. We carried on four field investigations on the site. A series of aerial photographs were acquired and completed by topographical measures on the ground. The morphology of the slide and its trajectory were reconstructed. To constrain the movement condition, we studied the internal structure of the source area and realized surveys among stakeholders of the dumpsite and citizen. Results 2.7 × 10 6  m 3 of waste materials spread 1000 m from the source in a rice field with an average thickness of 10 m. The material displays a preferential fabric parallel to the previous topography. Numerous internal slip surfaces, underlined by plastic bags explain the low friction coefficient. The presence of methane within the waste dump was responsible for explosions prior to sliding and for the fire that affects whole sliding mass. Conclusions Resulting of a combination of heavy rainfall and consecutive explosions due to biogas sudden release, this disaster was predictable in reason of i) a front slope of the dump of about 100% before the failure; ii) a poor dumpsite management; iii) the extreme vulnerability of the marginalized scavengers living at risk at the foot of the instable dump.

The present study pertains to the experimental work on the characteristic of a rotating liquid jet under various conditions of the nozzle diameter, volumetric flow rate and rotating speed. With emphasis on the important phenomena of a liquid jet, the effects of breakup length, the transition between dripping and jetting, breakup categories, droplet sizes from the breakup, and the time interval between two successive droplets are investigated systematically. The results reveal that the breakup length of a jet increases with flow rate and decreases with imposed rotation. The hysteresis behavior only occurs for larger nozzles, and the transition from jetting to dripping is affected by the imposed rotation. Depending on the imposed rotation, three different breakup patterns are found and named single droplet, satellite droplet, and multi-position necking. An empirical correlation is also proposed to predict the boundary of satellite and multi-droplets formation. The main droplet, satellite droplet, and merged droplet are about 1.8, 0.8, and 2.2 times than the nozzle diameters, respectively, no matter what the rotating speed is. Moreover, the non-dimensional time interval between two main droplets has an ascending tendency with either We number or the imposed rotation.

Blast-induced ground vibration has received much engineering and public attention. The vibration is often represented by the peak particle velocity (PPV) and the empirical approach is employed to describe the relationship between the PPV and the scaled distance. Different statistical methods are often used to obtain the confidence level of the prediction. With a known scaled distance, the amount of explosives in a planned blast can then be determined by a blast engineer when the PPV limit and the confidence level of the vibration magnitude are specified. This paper shows that these current approaches do not incorporate the posterior uncertainty of the fitting coefficients. In order to resolve this problem, a Bayesian method is proposed to derive the site-specific fitting coefficients based on a small amount of data collected at an early stage of a blasting project. More importantly, uncertainty of both the fitting coefficients and the design formula can be quantified. Data collected from a site formation project in Hong Kong is used to illustrate the performance of the proposed method. It is shown that the proposed method resolves the underestimation problem in one of the conventional approaches. The proposed approach can be easily conducted using spreadsheet calculation without the need for any additional tools, so it will be particularly welcome by practicing engineers.

To analyze the tension performance of laminated rubber bearings under tensile loading, a tension model for analyzing the rubber layers is proposed based on the theory of elasticity. Applying the boundary restraint condition and the assumption of incompressibility of the rubber layers, stress and deformation expressions for the tensile rubber layers are derived. Based on the derived expressions, the stress distribution and deformed pattern specifically for deformed shape of the free edges of rubber layers are analyzed, and the theory of cracking energy is applied to analyze the distributions of predicted cracking energy density and gradient direction. Prediction of crack initiation and crack propagation direction of the rubber layers is investigated. The analytical results show that the stress and deformation expressions can be used to simulate the stress distribution and deformed pattern of the rubber layer for laminated rubber bearings in the elastic range, and the crack energy method for predicting the failure mechanism is feasible according to the experimental phenomenon.

This paper reports on polarimetric radiation properties based on the switching modes of normal PSR B2020+28 by analyzing the data acquired from the Nanshan 25-m radio telescope at 1556 MHz. With nearly 8 hours quasi-continuous observation, the data presented some striking and updated phenomena. The change of relative intensity between the leading and trailing components is the predominant feature of mode switching. The intensity ratio between the leading and trailing components are measured for the individual profiles averaged over 30 seconds. It is found that there is an excess of high ratios over the normal distribution, which indicates that two modes exist in the pulsar. The distribution of abnormal mode has a narrower width indicating that the abnormal mode is more stable than the normal mode. A total of 76 mode switching events are detected in our data. It spends 89 % in the normal mode and 11 % in the abnormal mode. The intrinsic distributions of mode timescales are constrained with power-law distributions. The significant difference in the index of the duration distribution between normal and abnormal modes possibly indicates that the timescale for the abnormal mode to get stable is shorter than that for the normal mode. The frequent switching between both modes may indicate that the oscillations between different magnetospheric states are rapid.

We report on variations in the mean position angle of the 20 millisecond pulsars being observed as part of the Parkes Pulsar Timing Array (PPTA) project. It is found that the observed variations are dominated by changes in the Faraday rotation occurring in the Earth’s ionosphere. Two ionospheric models are used to correct for the ionospheric contribution and it is found that one based on the International Reference Ionosphere gave the best results. Little or no significant long-term variation in interstellar RM was found with limits typically about 0.1 rad m −2  yr −1 in absolute value. In a few cases, apparently significant RM variations over timescales of a few 100 days or more were seen. These are unlikely to be due to localised magnetised regions crossing the line of sight since the implied magnetic fields are too high. Most probably they are statistical fluctuations due to random spatial and temporal variations in the interstellar electron density and magnetic field along the line of sight.

Ecological rehabilitation using woody plants on roadside slopes has been gaining momentum in promoting urban biodiversity since 21st century. Many native tree and shrub species have been used for planting on roadside slopes. Yet, there is limited information in the local forestry and engineering literature on the mechanical properties and their relationship with above-ground characteristics, and the establishment method of native woody plants for shallow slope stabilisation. In this study, field pull-out tests were conducted to investigate the anchorage ability of two shrub (Rhodomyrtus tomentosa and Melastoma sanguineum) and two trees (Schefflera heptaphylla and Reevesia thyrsoidea) species. They have been commonly used in roadside slope rehabilitation in recent years. Samples were taken from planted and wild individuals. The plant pull-out resistance quantifies the degree of root reinforcement. The results showed that around 1 to 6 kN was required to uproot a 2 m plant. Trees exhibited better pull-out performance than shrubs. The planted trees had significantly stronger anchorage than natural ones. All the potential native plant species for slope rehabilitation should be screened by field pullout test, to ensure their achievement of both urban biodiversity enhancement and slope stabilisation purposes.