A theoritical approach to the study of compaction bands in porous rocks

The formation and propagation of compaction bands in high porosity sandstones is theoretically investigated in this paper using a new constitutive model based on the recently developed continuum breakage mechanics theory [1,2]. This model possesses a micromechanics-based link between the evolving grain size distribution (gsd) and the macroscopic stress strain relationship, through an internal variable called Breakage. This is an advanced feature over many existing plasticity based models in the literature, helping to faithfully track the evolving gsd and its related physics (e.g. permeability reduction). A localization analysis based on the acoustic tensor [3] is performed to determine both the onset and orientation of compaction bands due to grain crushing. It is shown that the model used is able to capture well both the material behaviour and formation of compaction band experimentally observed. An enhancement using rate-dependent regularization is applied to the model to deal with instability issues in the analysis of Boundary Value Problems. Based on the regularised model, the formation and propagation of compaction bands due to grain crushing is analysed through a numerical experiment on a porous rock specimen under triaxial loading condition. Good agreement between numerical predictions and experimental observations demonstrates the capability of the new model

S-PRAC: Fast Partial Packet Recovery with Network Coding in Very Noisy Wireless Channels

Well-known error detection and correction solutions in wireless communications are slow or incur high transmission overhead. Recently, notable solutions like PRAC and DAPRAC, implementing partial packet recovery with network coding, could address these problems. However, they perform slowly when there are many errors. We propose S-PRAC, a fast scheme for partial packet recovery, particularly designed for very noisy wireless channels. S-PRAC improves on DAPRAC. It divides each packet into segments consisting of a fixed number of small RLNC encoded symbols and then attaches a CRC code to each segment and one to each coded packet. Extensive simulations show that S-PRAC can detect and correct errors quickly. It also outperforms DAPRAC significantly when the number of errors is high

Numerical investigation of the impact behaviour of bioinspired nacre-like aluminium composite plates

Inspired by the hierarchical structure of nacre, an aluminium alloy (AA) 7075 based composite featuring layer waviness and cohesive interface is studied as a low weight impact resistant material. To investigate the mechanical response and the ballistic performance of this laminated structure, a numerical study of the proposed nacre-like composite plates made of 1.1-mm thick AA 7075 tablets bonded with toughened epoxy resin was performed using Abaqus/Explicit. Target thicknesses of 5.4-mm, 7.5-mm and 9.6-mm impacted by a rigid hemi-spherical projectile were simulated. The epoxy material was modelled using a user-defined interface cohesive element with compressive strength enhancement. A significant performance improvement was recorded for the 5.4-mm nacre-like plate (compared to the same thickness bulk plate), which was explained by the hierarchical structure facilitating both localised energy absorption (by deformation of the tablet) and more globalized energy absorption (by inter-layered delamination and friction). For a given projectile, however, the performance improvement of using the proposed composite decreased with increasing laminate thickness, which was attributed to the increased likelihood of ductile failure occurring prior to perforation in thicker bulk plates. For 5.4-mm thick plates impacted at high velocity, the nacre-like plate had a better ballistic performance than that of the plates made of continuous (flat and wavy) layers, which was attributed to the larger area of plastic deformation (observed in the nacre-like plate after impact) due to the tablets arrangement.The Australian Research Council Centre of Excellence for Design in Light Metals (CE0561574); National Natural Science Foundation of China (No. 11232003); The Australian Research Council via project DP1093485

A numerical study of bioinspired nacre-like composite plates under blast loading

In this paper, a multi-layered composite inspired by the hierarchical structure of nacre and made of layers of aluminium alloy AA 7075 bonded with toughened epoxy resin is introduced for blast resistant applications. The performance of the proposed nacre-like 3.3-mm and 5.4-mm thick composite plates, made of 1.1-mm thick AA 7075 layers, under localised impulsive loading was numerically studied. The epoxy material was modelled using user-defined interface cohesive elements that properly take into account both strength and toughness enhancements under compression. As compared to bulk plates, the improvement in blast resistance performance was numerically observed in the nacre-like plates, which required larger loads to reach the onset of failure. In addition, a reduction of the peak velocity and maximum deflection of the back face was observed for the nacre-like plates. This improvement is explained by the hierarchical structure facilitating a globalized energy absorption by inter-layer interlocking, delamination and friction.Australian Research Council through Centre of Excellence for Design in Light Metals (CE0561574). Discovery Projects (DP140100945 and DP1093485). The National Natural Science Foundation of China (No. 11232003)

Numerical modeling of thermal dust polarization from aligned grains in the envelope of evolved stars with updated POLARIS

Magnetic fields are thought to influence the formation and evolution of evolved star envelopes. Thermal dust polarization from magnetically aligned grains is potentially a powerful tool for probing magnetic fields and dust properties in these circumstellar environments. In this paper, we present numerical modeling of thermal dust polarization from the envelope of IK Tau using the magnetically enhanced radiative torque (MRAT) alignment theory implemented in our updated POLARIS code. Due to the strong stellar radiation field, the minimum size required for RAT alignment of silicate grains is $\sim 0.005 - 0.05\,\rm\mu m$. Additionally, ordinary paramagnetic grains can achieve perfect alignment by MRAT in the inner regions of $r < 500\,\rm au$ due to stronger magnetic fields of $B\sim 10$ mG - 1G, producing thermal dust polarization degree of $\sim 10\,\%$. The polarization degree can be enhanced to $\sim 20-40\%$ for grains with embedded iron inclusions. We also find that the magnetic field geometry affects the alignment size and the resulting polarization degree due to the projection effect in the plane-of-sky. We also study the spectrum of polarized thermal dust emission and find the increased polarization degree toward $\lambda > 50\,\rm\mu m$ due to the alignment of small grains by MRAT. Furthermore, we investigate the impact of rotational disruption by RATs (RAT-D) and find the RAT-D effect cause a decrease in the dust polarization fraction. Finally, we compare our numerical results with available polarization data observed by SOFIA/HAWC+ for constraining dust properties, suggesting grains are unlikely to have embedded iron clusters and might have slightly elongated shapes. Our modeling results suggest further observational studies at far-infrared/sub-millimeter wavelengths to understand the properties of magnetic fields and dust in AGB envelopes.Comment: 27 pages, 23 figures, 1 table, to be submitte

UC-69 Team 10B BChain

BChain is a new P2P file sharing system that is fully private, anonymous, globally self-verifying, and utilizes an automatic peer-maintained network of trust in data, accomplished through new methods of routing content over the whole network, encrypted, rather than per torrent download. Verification is done by adding file metadata to a blockchain giving the network consistent knowledge of each file it can transfer, and how to verify file received against the network. This enables a policy of zero trust against peers. This system is implemented by an app that interfaces with the network using the protocol, using it for upload, download and file discovery. The interface is built using web technologies, which allows for flexible use across native platforms.Advisors(s): Prof. Ken HogansonTopic(s): IoT/Cloud/NetworkingCS 485

The Cenozoic Song Hong and Beibuwan Basins, Vietnam

The Vietnamese offshore margin holds a substantially underexplored petroleum potential. The key to unravelling this potential lies in understanding the tectono-stratigraphic framework of the region including the Cenozoic mechanisms governing syn-rift and source rock deposition. This is essential for prediction of, for instance the presence and nature of source rocks in South-East Asia and possible reservoir intervals in the syn-rift packages. The Vietnamese part of the Song Hong and Beibuwan Basins (Fig. 1) differs from other basins along the western margin of the South China Sea in that the Palaeogene syn-rift succession is sporadically exposed due to uplift and inversion. These exposures provide a unique glimpse into the Cenozoic syn-rift succession of the basin