Sharif Digital Repository

A study has been carried out of the effect of an anodizing pre-treatment in a sulphuric acid electrolyte on the strength of AA 5052 alloy/polypropylene joints prepared using friction stir spot welding. Lap-shear tests were used to determine the joint strength. Comparisons were made with joints pre-treated using sand blasting. The failed specimens were examined by scanning and transmission electron microscopy. Anodizing improved the strength of the joints by a factor of about 6 compared with sandblasting. For the anodizing pre-treated joints, melted polymer infiltrated deeply within the nanoporous anodic film, forming a strong polymer-film bond. Joint failure occurred by ductile tearing of... 

In this paper, an advanced integrated pixel-level method based on the deep convolutional neural network (DCNN) approach named DeepLabv3+ is proposed for weak interlayers detection and quantification. Furthermore, a database containing 32,040 images of limestone, dolomite, loess clay, and red clay is established to verify this method. The proposed model is then trained, validated, and tested via feeding multiple weak interlayers. Moreover, robustness and adaptability of the proposed model are evaluated, and the weak interlayers are extracted. Compared with the fully convolutional network (FCN)-based method and traditional image techniques, the proposed model provides higher accuracy in terms... 

The treatment of refractory wastewater and energy utilization are challenging environmental issues. Carbonate as the most common anion abounds in the aquatic environment. Here, we proposed a novel method to degrade carbonate-containing wastewater and simultaneous electricity generation via the combined oxidation of CO3[rad]− and O2[rad]− radicals. The CO3[rad]− radical was produced by the photoelectrode of TiO2/Si photovoltaic cell with the rear Si photovoltaic cell providing external bias, and the O2[rad]− radical was produced from the generation of H2O2 on a gas diffusion electrode (GDE), and they were both further enhanced from the activation reaction of H2O2 with HCO3− electrolyte. The... 

H2S and CO2 are the main impurities in raw natural gas, which needs to be purified before use. However, the comprehensive utilization of H2S and CO2 has been ignored. Herein, we proposed a fully resource-based method to convert toxic gas H2S and greenhouse gas CO2 synchronously into CO and elemental S by using a novel electrochemical reactor. The special designs include that, in the anodic chamber, H2S was oxidized rapidly to S based on the I−/I3− cyclic redox system to avoid anode passivation. On the other hand, in the cathodic chamber, CO2 was rapidly and selectively reduced to CO based on a porous carbon gas diffusion electrode (GDE) modified with polytetrafluoroethylene and cobalt... 

Urea is a major source of nitrogen pollution in domestic sewage and its denitrification is difficult since it is very likely to be converted into ammonia or nitrate instead of expected N2. Herein, we propose an exhaustive denitrification method for urea via the oxidation of amine/ammonia-N with chlorine oxide radical, which induced from a bi-functional RuO2//WO3 anode, and the highly selective reduction of nitrate-N on cathode in photoelectrochemical cell (PEC). Under illumination, the WO3 photoanode side promotes the quantities hydroxyl and reactive chlorine radical, and these radicals are immediately combined to stronger chlorine oxide radical by RuO2 side, which obviously enhances the... 

There is growing interest in applying distributed machine learning to edge computing, forming federated edge learning. Federated edge learning faces non-i.i.d. and heterogeneous data, and the communication between edge workers, possibly through distant locations and with unstable wireless networks, is more costly than their local computational overhead. In this work, we propose ${{sf DONE}}$DONE, a distributed approximate Newton-type algorithm with fast convergence rate for communication-efficient federated edge learning. First, with strongly convex and smooth loss functions, ${{sf DONE}}$DONE approximates the Newton direction in a distributed manner using the classical Richardson iteration... 

TiO2 is a promising photoanode material for photoelectrochemical (PEC) water splitting, but its severe bulk recombination of photogenerated carriers, sluggish oxygen evolution reaction (OER) kinetics and poor visible light response are the main bottleneck problems. Here, the carbon quantum dots (CQDs) modified anatase/rutile TiO2 photoanode (CQDs/A/R-TiO2) was designed by growth of anatase TiO2 nanothorns on rutile TiO2 nanorods and further surface modification of CQDs. The results revealed that the A/R-TiO2 heterojunction significantly suppressed the bulk recombination of photogenerated carriers. With further incorporation of CQDs into A/R-TiO2, dramatical improvement of OER kinetics and... 

A study has been carried out of the effect of plasma electrolytic oxidation (PEO)on the strength of AA 5052 alloy/polypropylene joints prepared using friction stir spot welding (FSSW). The joint strengths were determined using lap-shear tests and failure modes were investigated using scanning electron microscopy. Comparisons were made between control joints prepared with the alloy in the as-rolled condition or the as-rolled condition with a mechanical key and with PEO-treated alloy, with or without a mechanical key. Mechanical keying alone, provided by infiltration of polymer into holes of either 3 or 4.5 mm diameter drilled in the alloy, yielded enhancements of the joint strength by a... 

The power control of horizontal axis wind turbines can affect significantly the vibration loads and fatigue life of the tower and the blades. In this paper, we both consider the power control and vibration load mitigation of the tower fore-aft vibration. For this purpose, at first, we developed a fully coupled model of the NREL 5MW turbine. This model considers the full aeroelastic behaviour of the blades and tower and is validated by experiment results, comparing the time history data with the FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code which is developed by NREL (National Renewable Energy Lab in the United States). In the next, novel sensorless control algorithms are... 

Floquet dynamical quantum phase transitions (FDQPTs) are signified by recurrent nonanalytic behaviors of observables in time. In this work, we introduce a quench-free and generic approach to engineer and control FDQPTs for both pure and mixed Floquet states. By applying time-periodic modulations with two driving frequencies to a general class of spin chain model, we find multiple FDQPTs within each driving period. The model is investigated with equal, commensurate and incommensurate driving frequencies. The nonanalytic cusps of return probability form sublattice structures in time domain. Notably, the number and time locations of these cusps can be flexibly controlled by tuning the... 

The expected lifetime of a power electronic converter is limited by its fragile components such as semiconductor devices and capacitors. These components are prone to wear-out failures depending on the converter mission profile and component thermal characteristics. This paper explores the wear-out failure of the power converter semiconductor devices in inverting and rectifying modes of the converter using different power factors. The obtained results show the different wear-out characteristics of a converter under rectification, inversion, and also partial-inversion/rectification modes as well as when provides reactive power support. Moreover, this paper proposes B10 lifetime curves to... 

Natural gas hydrate, a crystalline solid existing under high-pressure and low-temperature conditions, has been regarded as a potential alternative energy resource. It is globally widespread and occurs mainly inside the pores of deepwater sediments and sediments under permafrost area. Hydrate production via well depressurization is deemed well-suited to existing technology, in which the pore pressure is lowered, the natural gas hydrate is dissociated into water and gas, and the water and gas are produced from well. This method triggers multiphysics processes such as fluid flow, heat transfer, energy adsorption, chemical reaction and sediment deformation, all of which are dependent on the... 

This paper presents a review of the existing models for the estimation of explosion-induced crushed and cracked zones. The control of these zones is of utmost importance in the rock explosion design, since it aims at optimizing the fragmentation and, as a result, minimizing the fine grain production and recovery cycle. Moreover, this optimization can reduce the damage beyond the set border and align the excavation plan with the geometric design. The models are categorized into three groups based on the approach, i.e., analytical, numerical, and experimental approaches, and for each group, the relevant studies are classified and presented in a comprehensive manner. More specifically, in the... 

The seismic response of soil depends on proper evaluation and use of soil dynamic properties, including shear modulus and damping ratio at various strain levels. Despite extensive studies on the shear modulus and damping ratio of saturated soils, research on the dynamic properties of unsaturated fine-grained soils — especially at high suction — is limited. This study aims to investigate the dynamic properties of loess at a variety of initial states resulting from different specimen preparation techniques (reconstituted, recompacted, and intact) and their evolutions due to suction-induced desiccation. Results of resonant column tests show that at initial states, the specimen preparation... 

The on-fiber standardization technique for solid-coated solid-phase microextraction (SPME) was studied, and a theoretical model is proposed for the isotropic behavior of adsorption and desorption, based on Fick's law of diffusion and the Langmuir model. The isotropy of the adsorption and desorption of analytes onto and from the surface of porous solid SPME fiber was validated with the use of a commercially available fiber, a 50-μm Carbowax/ templated resin for carbamate pesticide analysis in various sample matrixes, and a self-made polypyrrole fiber for diazepam analysis in blood samples. Time constants were comparable for the adsorption and desorption processes. Equilibrium constants and... 

In this study, the enhanced trichloroethylene (TCE) degradation performance was investigated by polyvinyl alcohol coated calcium peroxide nanoparticles (PVA@nCP) as an oxidant in Fe(II)-based catalytic systems. The nanoscale iron sulfide (nFeS), having an average particle size of 115.4 nm, was synthesized in the laboratory and characterized by SEM, TEM, HR-TEM along with EDS elemental mapping, XRD, FTIR, ICP-OES, and XPS techniques. In only ferrous iron catalyzed system (PVA@nCP/Fe(II)), TCE degradation was recorded at 58.9% in 6 h. In comparison, this value was increased to 97.5% or 99.7% with the addition of citric acid (CA) or nFeS in PVA@nCP/Fe(II) system, respectively. A comparative... 

In this study, the enhanced trichloroethylene (TCE) degradation performance was investigated by polyvinyl alcohol coated calcium peroxide nanoparticles (PVA@nCP) as an oxidant in Fe(II)-based catalytic systems. The nanoscale iron sulfide (nFeS), having an average particle size of 115.4 nm, was synthesized in the laboratory and characterized by SEM, TEM, HR-TEM along with EDS elemental mapping, XRD, FTIR, ICP-OES, and XPS techniques. In only ferrous iron catalyzed system (PVA@nCP/Fe(II)), TCE degradation was recorded at 58.9% in 6 h. In comparison, this value was increased to 97.5% or 99.7% with the addition of citric acid (CA) or nFeS in PVA@nCP/Fe(II) system, respectively. A comparative... 

Joining of dissimilar light metals by friction stir welding (FSW) is of interest to reduce weight and fuel consumption in the transport sector. Such coupled metals may need protective surface treatments, e.g. against wear or corrosion, for some applications. In this work, the formation of plasma electrolytic oxidation (PEO) coatings in a silicate-based electrolyte for corrosion protection of FSW AZ31B magnesium alloy-titanium joints has been studied. The joints, if unprotected, may be susceptible to severe galvanic corrosion in chloride-containing environments. The coatings were characterized by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. Mg2SiO4 and... 

To investigate the influences of microstructure changes on dilatancy of unsaturated loess at high suctions, a direct shear box device using the vapour equilibrium technique was used. Through conducting two series of direct shear tests on both intact and recompacted loess specimens and also investigating microstructural changes using the mercury intrusion porosim-etry (MIP) technique, a linear increase in dilatancy with suctions ranging from 8 to 230 MPa can be identified at different net stresses. The enhanced dilatancy observed is mainly attributed to desiccation-induced high suctions as the reduction in void ratio due to enhancement of suction was negligible. A macrovoid ratio, eM, may be...