Modeling and analysis of wormhole formation in reactive dissolution of carbonate rocks

A two-scale continuum model is used to simulate reactive dissolution of carbonate rocks in radial flow. The three main types of patterns observed in linear and radial flow experiments, namely, compact, wormhole and uniform patterns are numerically simulated. The fractal nature of wormholes observed in laboratory experiments is established and confirmed through simulations and the fractal dimension is quantitatively matched. The dependence of wormhole fractal dimension, optimum injection rate and minimum pore volumes required to breakthrough the medium on heterogeneity magnitude and aspect ratio is investigated. A new criterion to predict the optimum injection rate for wormhole formation in radial flow is derived and validated. It is observed that the wormhole penetration depth increases with injection time as t^b, where the exponent b is found to be approximately 0.66, as observed in the experiments. A critical level of heterogeneity magnitude seems to exist below which the minimum pore volumes required to breakthrough are much higher.     

Fabrication of dense Ce0.9Mg0.1P2O7-PmOn composites by microwave heating for application as electrolyte in intermediate-temperature fuel cells

In the present work, we report a method of fabrication of dense 10 mol% Mg²⁺-doped cerium pyrophosphate-phosphate (Ce_0.9Mg_0.1P₂O₇-P_mO_n; CMP-P) composites by microwave heat-treatment of the preformed Ce_0.9Mg_0.1P₂O₇ substrates in the presence of phosphoric acid. The composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The microwave heating at 375 °C for 5 min resulted in the formation of dense CMP-P composites which retained most of the pyrophosphate phase. The electrical conductivity was extracted from the EIS data and for the CMP-P composite prepared by H₃PO₄ loading for 10 h and microwave heat-treatment for 5 min it was found to be >10^?2 S m^?1 in 100–250 °C range with a maximum of 0.062 S cm^?1 at 190 °C, which was significant for its application as electrolyte in intermediate temperature fuel cells.     

Non-destructive Evaluation and Development of a New Wire Rope Tester Using Parallely Magnetized NdFeB Magnet Segments

A new wire rope tester based on principle of magnetic flux leakage is constructed. Two rings of NdFeB are cut in axial direction into 32 equal arc segments such that each arc segment subtends an angle of 22.5° at the centre. These arc segments are then parallely magnetized in magnetizer. A ferromagnetic cylinderical yoke is constructed by hinging two ferromagnetic half cylinders along one axial edge. A fixture consisting of a wooden square base, wooden mandrel, stepped and slotted Aluminium cylinder and Aluminium fillers is made to assemble the NdFeB magnets in a ring on both the ends of the ferromagnetic yoke. A Hall effect sensor is instrumented inside the yoke in the middle at radial distance of 34 mm from the axis of the yoke. A ferromagnetic wire rope with a defect is inserted in the novel wire rope tester. It has been successfully shown by performing Non-destructive testing that whenever a defect in a wire rope passes below the Hall-effect sensor instrumented in the wire rope tester developed in this work, a signal is generated indicating the defect.     

Nickel decorated MoO3 single crystal microflakes with multi-site functionality for enhanced hydrogen evolution reaction

Role of hybrid material with metal-oxide interface has been explored by coating 2 nm nickel on α-MoO₃ single crystals for hydrogen evolution reaction (HER). The investigated aspects reveal that α-MoO₃/Ni hybrid exhibits a remarkable performance in HER showing +6 mV onset potential and 37 mV overpotential at 10 mA/cm² current density along with Tafel slope of 47 mV/dec. The single crystalline-stepped CVD-grown MoO₃ microflakes having the advantage of higher hydrogen binding energy of Ni exhibits the enhanced catalytic performance due to strong electronic coupling at the metal-oxide interface and hydrogen spill over effect. Similar hybrid material composed of Cu-MoO₃ does show improvement but not as good as Ni-MoO₃. A decrease of ~36% is observed in the overpotential for Ni-coated MoO₃ compared to pure MoO₃ crystals indicating the positive contribution of Ni-coating. The hybrid Ni-MoO₃ shows the new route to develop alternate transition metal oxide-based hybrid catalyst towards production of hydrogen fuel.     

Design and Analysis of Multiband Fractal Antenna for MIMO/Diversity Applications

In this article a modified hybridized fractal geometry i.e., fractal antenna is proposed for Multiple Input Multiple Output (MIMO) applications. These geometries are based on Minkowski curves and Koch curves located around the boundaries of the microstrip patch of rectangular-shaped patch. The hybridized model for fractal geometry is designed and analyzed on an FR4 substrate having a thickness of 1.47 mm for the Industrial, Scientific, and Medical (ISM) frequency band. But due to the proposed fractal geometry, it resonates at three bands (2.45 GHz, 3.67 GHz, and 5.88 GHz) and it is covering the ISM band from 2.42 GHz to 2.48 GHz with a VSWR value is 1.48. Further, a 2?×?2 antenna for MIMO application is proposed by considering identical antenna elements placed in parallel on the same substrate. MIMO antenna resonates at three frequencies as same as single antenna elements and covering the same operating bands. The two elements of MIMO confguration are simulated for various sets of distance values, and optimized distance is obtained 18 mm at which a proposed antenna provides low mutual coupling value, low Envelope Correlation Coefficient (ECC), and high diversity and peak gain. The calculated values of ECC and diversity gain are 0.0002 and 10 dB, respectively which satisfy the criteria of MIMO application. The design has been experimentally validated and an appropriate similarity of experimental and simulated results is achieved.

     

Effect of medium heterogeneities on reactive dissolution of carbonates

The influence of medium heterogeneities on wormhole formation in carbonates is studied using a two-scale continuum model. The model describes the coupling between the transport and reaction processes occurring at the pore and Darcy scales. The medium heterogeneity is represented through initial porosity (or permeability) field by introducing a randomly generated normal distribution of local porosity values. Heterogeneity in the rock is characterized by the magnitude of maximum variation in local porosity value from the average porosity and by the length scale over which this variation occurs. It is found that heterogeneity in a rock affects not only the structure of the patterns formed during reactive dissolution but also the amount of acid required to achieve a given increase in permeability. The volume of acid required decreases as the heterogeneity magnitude or length scale are increased and this is particularly noticeable at high injection rates of acid. At intermediate injection rates, the required acid volume decreases gradually and an optimum value in heterogeneity magnitude may exist. This has been attributed to excessive branching in a pattern when the medium becomes extremely heterogeneous. In addition, the amount of acid required to breakthrough is found to depend on the initial rock porosity and dimensions of the rock being acidized. Finally, a novel way to characterize heterogeneity is defined, where heterogeneity at the core-scale is expressed using a heterogeneity parameter, ? as a product of the heterogeneity magnitude and length scale, and is validated for a given rock type at different injection conditions.     

Alzheimer's detection using various feature extraction approaches using a multimodal multi-class deep learning model

Alzheimer's disease is a chronic brain condition that takes a toll on memory and potential to do even the most basic tasks. With no specific solution viable at this time, it's critical to pinpoint the start of Alzheimer's disease so that necessary steps may be initiated to limit its progression. We used three distinct neuroanatomical computational methodologies namely 3D-Subject, 3D-Patches, and 3D-Slices to construct a multimodal multi-class deep learning model for three class and two class Alzheimer's classification using T1w-MRI and AV-45 PET scans obtained from ADNI database. Further, patches of various sizes were created using the patch-extraction algorithm designed with torch package leading to separate datasets of patch size 32, 40, 48, 56, 64, 72, 80, and 88. In addition, Slices were produced from images using either uniform slicing, subset slicing, or interpolation zoom approaches then joined back to form a 3D image of varying depth (8,16,24,32,40,48,56, and 64) for the Slice-based technique. Using T1w-MRI and AV45-PET scans, our multimodal multi-class Ensembled Volumetric ConvNet framework obtained 93.01% accuracy for AD versus NC versus MCI (highest accuracy achieved using multi-modalities as per our knowledge). The 3D-Subject-based neuroanatomy computation approach achieved 93.01% classification accuracy and it overruled Patch-based approach which achieved 89.55% accuracy and Slice-Based approach that achieved 89.37% accuracy. Using a 3D-Patch-based feature extraction technique, it was discovered that patches of greater size (80, 88) had accuracy over 89%, while medium-sized patches (56, 64, and 72) had accuracy ranging from 83 to 88%, and small-sized patches (32, 40, and 48) had the least accuracy ranging from 57 to 80%. From the three independent algorithms created for 3D-Slice-based neuroanatomy computational approach, the interpolation zoom technique outperformed uniform slicing and subset slicing, obtaining 89.37% accuracy over 88.35% and 82.83%, respectively. Link to GitHub code: https://github.com/ngoenka04/Alzheimer-Detection .