•Characterization of blast-induced damage zone in the presence of far field stresses.•Studied the efficiency of current destress blasting patterns in deep excavations.•Introduced a new destressing ...pattern for stress transformation ahead of tunnel face.
The controlled use of explosives for the purpose of introducing fractures to the rock material in deep underground mining and tunneling activities is considered one of the tactical approaches to alleviate the mining induced rockburst potential at great depth. Rockbursts, which are associated with sudden release of the strain energy stored in brittle rock, are considered safety risks for the personnel and lead to production disruption imposing economic threats. Preconditioning of the rock mass ahead of a tunnel development face can be achieved using destress blasting techniques in order to dissipate the stored strain energy in the stress concentration zones by damaging the rock. Such technique will eventually transform the stress states ahead of the tunnel face where the magnitude of the peak stresses is reduced and pushed further away from tunnel face. This paper studies numerically the extent of the blast-induced damage zones in underground excavation activities in the presence of anisotropic principal stresses. The effectiveness of the current destressing blast patterns is investigated and the resulted damage zones and the stress states before and after destressing in studied. A new destress blasting pattern is introduced in which the blast-induced damage zone is capable of effectively transforming the stress states ahead of a tunnel development face.
Rock fragmentation by blasting is the most efficient way of rock breakage in hard rock mining applications. Fragmentation, as well as the properties of the fragments generated by the explosion, are ...of significant concern as the energy consumption at the mill is greatly affected by them. Dynamic loading of blasting generates a countless number of microcracks in the host rock, which despite the major cracks forming the fragments could not get enough time to coalesce and create macrocracks. These microstructures eventually impact the integrity of the intact rock and reduce its strength. Damage is considered as a scalar parameter, which accounts for the creation of flaws and microstructures in the rock, deteriorating its elasticity modulus. The stress waves and their interactions are the parameters that control damage around blastholes. In this study, using LS-DYNA numerical code, the effect of initiation timing on blast-induced rock damage and fragmentation is investigated. The results of the numerical models reveal the importance of the delays in damage as well as fragment size distribution. Delayed initiation provides enough timing for the cracks to grow, which preconditions the surrounding rock for the neighboring blasthole. The interaction between the stress waves resulting from the detonation of neighboring blastholes plays an important role in damage and fragmentation analysis. The optimum delay time can be obtained by considering the rise time and the duration of the stress pulse, the P and S wave travel times in the host rock, and the crack propagation time within the rock burden.
Understanding the linear response of any system is the first step towards analyzing its linear and nonlinear dynamics, stability properties, as well as its behavior in the presence of noise. In ...non-Hermitian Hamiltonian systems, calculating the linear response is complicated due to the non-orthogonality of their eigenmodes, and the presence of exceptional points (EPs). Here, we derive a closed form series expansion of the resolvent associated with an arbitrary non-Hermitian system in terms of the ordinary and generalized eigenfunctions of the underlying Hamiltonian. This in turn reveals an interesting and previously overlooked feature of non-Hermitian systems, namely that their lineshape scaling is dictated by how the input (excitation) and output (collection) profiles are chosen. In particular, we demonstrate that a configuration with an EP of order M can exhibit a Lorentzian response or a super-Lorentzian response of order M
with M
= 2, 3, …, M, depending on the choice of input and output channels.
Layered double hydroxides (LDH) have shown to improve the zinc electrodeposition efficiency at the negative electrode of aqueous zinc‐ion batteries. In this work, a copper‐doped Zn−Al−CO3 layered ...double hydroxide (LDH) has been synthesized by co‐precipitation method under constant pH, and investigated as suitable solid‐state additive in zinc‐based negative electrodes. X‐ray diffraction patterns in combination with scanning electron microscope images show that the as‐synthesized LDHs are well crystalline and hexagonal platelet‐like. LDH was mixed with zinc powder in different ratios and the electrochemical performances of the mixtures were characterized by galvanostatic cycling with potential limitation (GCPL) at different current rates. The results show that an appropriate combination of zinc and LDH can be used to reach electrodeposition efficiency equal to 98 %. Thereafter, the performance of this electrode in a full cell is studied. In such configuration, the electrode shows that the electrodeposition efficiency remains high even at high current rates, which is an important characteristic for grid‐scale energy storage.
An inert kinetic booster: by mixing zinc powder with a layered double hydroxide it is possible to increase the zinc electro‐deposition efficiency from 88 % to 98 % in zinc‐ion batteries. The layered double hydroxide works as a passive substrate for the electro‐deposition process, offering a large surface area with low energy and decreasing the kinetic limitations. This allows reaching more than 250 charging cycles at 98 % efficiency with a C‐rate equal to 5.
Feature selection (FS) has shown remarkable performance in decreasing the dimensionality of high-dimensional datasets by selecting a good subset of features. Labeling high-dimensional data can be ...expensive and time-consuming as labeled samples are not always available. Therefore, providing effective unsupervised FS methods is essential in machine learning. This article provides a fuzzy multi-criteria decision-making method for unsupervised FS in which an ensemble of unsupervised FS rankers is utilized to evaluate the features. These methods are aggregated based on a fuzzy TOPSIS method. This is the first time a fuzzy multi-criteria decision-making approach has been used for an FS problem. Multiple comparisons are made to show the optimality and effectiveness of the proposed strategy against multiple competing FS methods. Our approach regarding two classification metrics, F-score and accuracy, appears superior to comparable strategies. Also, it is performing so swiftly.
Ecological capability evaluation is referred to as evaluation of potential capability of land and determination of its natural land use. In this paper, ecological capability of Lille Basin in Lahijan ...was evaluated for afforestation and forest expansion using Geographical Information Systems (GIS). For this purpose, information layers (slope, elevation, geographical directions, temperature, rainfall, humidity, soil type, and canopy cover) were prepared by digitizing the data obtained from concerned organizations. First, the layers were prepared based on coordinate systems and pixel value. Then, they were standardized using fuzzy membership functions. The evaluation criteria were prioritized with regard to expert opinion, and by using multi-criteria evaluation method (MCE) and analysis of hierarchic process (AHP), and the final weight of each criterion was determined. The weight for 8 criteria including elevation, soil type, canopy cover (%), directions, slope, temperature, humidity, rainfall were 0.330, 0.210, 0.128, 0.117, 0.076, 0.054, 0.046 and 0.210, respectively. According to these weights, elevation has the highest value and the slope is the lowest. The results suggest that ecological capability exhibits sensitivity to variations of different criteria and its distribution is directly correlated to ecological factors especially climatic and physiographical ones. The incompatibility index (0.09) also indicated that the weights were logical. Then valuation of the maps performed. Finally, based on these values, capabilities of each environmental unit were identified and potentials of the area for afforestation were determined in five capability classes.
The grain orientation dependence of the deformation-induced forward fcc→hcp and reverse hcp→fcc martensite transformation of a FeMnSi-based shape memory alloy was studied by in situ neutron ...diffraction during cyclic loading. A deformation-induced fcc→hcp transformation is observed during tensile straining to +2%. The hcp martensite phase that forms under tension partially reverts to fcc austenite upon subsequent compression from +2% → −2% for the {220}, {331} and {111} grain families aligned with respect to the loading direction but not for the {200} grain family. The martensite formation and the reversion of the individual grains can be explained by considering grain orientation dependent Schmid factors of the {111} slip system underlying the fcc to hcp transformation. While for post-yield elastically compliant grains the Schmid factor of the leading partial dislocation is larger than that of the trailing partial dislocation, the opposite is true for post-yield elastically stiff grains. The former grains show a phase reversion, i.e. hcp→fcc upon compression, the latter grains do not transform back to fcc. EBSD characterization confirms the phase reversion for a orientated grain by the disappearance of hcp bands. Martensite bands, which have not reverted to austenite during compression, showed a thickening. The thickening of existing bands during compression is associated with the activation of a second slip system.
•In situ cyclic deformation experiments with in FeMnSi alloy during neutron diffraction.•Deformation induced fcc.→hcp and its reversion hcp→fcc in FeMnSi was studied.•Grain orientation determines the amount of martensite formation and its reversion.•Two fundamentally different transformation behaviors are identified.•For strains <2% one primary slip plane is active during tension and compression.
The aim of this study is to investigate the effect of polymer nature on the morphology of synthesized nanoparticles. Super paramagnetic iron oxide nanoparticles (SPIONs) were prepared by ...co-precipitation method and then reacted with (3-mercaptopropyl) trimethoxysilane to obtain thiol-decorated SPIONs. Acrylated poly(caprolactone) and methoxy poly(ethylene glycol) were prepared, and then "thiol-ene click" reaction was performed under UV irradiation to attach two types of polymers on the surface of magnetite nanoparticles
via
the "photo-click" reaction method. Computational modelling was used for the prediction of the self-assembly of polymers on the surface of SPIONs, which determines the morphology of polymer coated nanoparticles.
Different structures ranging from "Janus" to "homogeneously mixed systems" were prepared through the proper adjustment of the PEG and PCL ratios.
The creep and stress relaxation behavior of a Fe–17Mn–5Si–10Cr–4Ni–1(V,C) (wt%) shape memory alloy at low homologous temperatures (−45°C<T<50°C) was systematically studied in stress and strain ...controlled tensile tests. At constant stresses at −45°C, the alloy exhibits pronounced creep up to 0.6% at 600MPa after only 30min holding time. If the strain is kept constant, a pronounced stress relaxation of up to 10% of the initial stress was observed. The final creep strains, the creep rates at a constant stress as well as the stress relaxation at a constant strain increase with decreasing temperature. In addition, the change of the recovery stress as a function of time in a restrained sample after 4% elongation and heating to different constant temperatures was monitored. It was observed that the increase of the final recovery stress is more pronounced when the holding temperature is increased. This behavior was explained with the time and temperature dependent formation of stress induced ε-martensite from the parent γ-austenite phase during mechanical loading according to the model of Kajiwara et al. as well as with the increased number of stacking faults at lower temperatures, which serve as nucleation sites for the ε-martensite formation.
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