Use of a Trial Function Method to Semi-analytically Simulate Matrix Diffusion in Heterogeneous and Fractured Media

A semi-analytic trial function model is applied to simulate matrix diffusion in systems of parallel fractures, 2-D/3-D discrete fracture networks, and in 3-D heterogeneous media. The trial function model gives low normalized root mean square error (NRMSE) when compared to the parallel fracture analytical solution over a range of fracture spacing, with considerations for retardation and decay. The semi-analytic trial function model is efficient in time and maintains less than 6% NRMSE when it simulates matrix diffusive transport in 2-D/3-D discrete fracture networks (DFN). The model can predict DFN plume within a few meters of accuracy compared to fine-grid DFN models. In two material distributions of a heterogeneous media, the semi-analytic model is similarly efficient and accurate. The matrix diffusion modeling parameters of the trial function model can be directly computed in fractured and porous media using either the fracture properties or subsurface core/boreholes. An effort to improve the semi-analytic model by including a variable diffusion area is considered. The use of the variable diffusion area yields about a 5% gain in accuracy. In contrast to the semi-analytic trial function model, the dual-porosity model is shown to be a less robust equivalent porous media approach. The dual-porosity model relies on a first-order mass transfer coefficient, which is time-dependent. The mass transfer coefficient can be initially estimated as the inverse of the characteristic diffusion time. The dual-porosity model gives low NRMSEs in small fracture spacing cases. However even with calibration, in cases of large fracture spacing, the dual-porosity model is unable to match analytical solutions and fine-grid results

Synthesis Of -Tcp Powder Via Wet Precipitation And Hydrothermal Methods

Matlamat kajian ini adalah untuk mensintesis β-TCP [β-Ca3(PO4)2] menggunakan Ca(OH)2 dan H3PO4 sebagai bahan mula. The purpose of this study is to synthesize β-TCP [β-Ca3(PO4)2] using Ca(OH)2 and H3PO4 as the starting material

PROMOTING ASPECT OF PALLADIUM NANOPARTICLES ON SPINEL Pd@CuCr2O4/γ–Al2O3 CATALYTIC SYSTEM IN CARBON MONOXIDE OXIDATION

In this report, the promoting aspect of Pd on the activity of spinel CuCr2O4 and Pd catalytic systems in CO oxidation is investigated. Catalysts with compositions of 10 % spinel CuCr2O4 synthesized via modified sol–gel in situ on γ–Al2O3 support and Pd nanoparticles (0.11 ÷ 0.68) % then decorated on CuCr2O4/γ–Al2O3 via impregnation method by decomposed palladium (II) acetate solution at 280 °C for 2 h. Promoting aspect of Pd nanoparticles evaluating by Temperature Program Surface Reaction (TPSR) method in temperature range of 30 ÷ 450 °C and 15 L.h–1 flow gases consist of 1 % CO, 20 % O2 and 79 % N2 on 0.100 g catalysts. The experimental results reveal that the as–prepared materials completely convert CO at temperatures below 140 °C with 0.68 % Pd compare to 300 °C without Pd in the component. CO conversion highly increases with increasing amounts of Pd, with gas hourly space velocity reached by 1500 L.h–1.g–1 that exhibits promising application of these catalytic systems in exhausts treatment containing CO at low temperatures

Synthesis Of B-TCP Powder Via Wet Precipitation And Hydrothermal Methods [R857.M3 P534 2007 f rb].

Matlamat kajian ini adalah untuk mensintesis β-TCP [β-Ca3(PO4)2] menggunakan Ca(OH)2 dan H3PO4 sebagai bahan mula. Dua pendekatan telah digunakan dalam kajian ini untuk menghasilkan β-TCP, iaitu kaedah pemendakan basah dan kaedah hidtroterma. The purpose of this study is to synthesize β-TCP [β-Ca3(PO4)2] using Ca(OH)2 and H3PO4 as the starting material. Two approaches were used in this work to produce β-TCP, namely a precipitation method and a hydrothermal method

Influence of temperature on mechanical characteristics of 1018 low carbon steel estimated by ultrasonic non-destructive testing method

The temperature dependence of ultrasonic velocities propagated in low carbon steel 1018 has been investigated by the A-scan mode of the ultrasonic non-destructive testing method. Experimental results show that these velocities are linearly dependent on temperature of the carbon steel sample in the range of 0 to 50 °C. Based on the experimental velocities of the longitudinal wave and the shear one, mechanical characteristics of this carbon steel including Poisson's ratio (υ), Young’s modulus (E), shear modulus (G), and bulk modulus (K) have been calculated. These mechanical characteristics have also been linear response with respect to the increase of sample’s temperature. By using linear fitting approach, the temperature dependence coefficients of these mechanical characteristics have been analyzed and estimated to be 9.76×10-6/°C, −0.057 GPa/°C, −0.023 GPa/°C, and −0.038 GPa/°C for v, E, G, and K, respectively. It is concluded that the influence of the temperature on the mechanical properties of the carbon steels is necessary determined due to the improved accuracy of the ultrasonic testing method

Shaping supply chain governance

The production process is becoming more complex and involving multiple companies and countries. A lot of research has focused on how these activities are coordinated and how interfirm transactions are governed. However, the existing literature is neither complete nor clear enough to understand how external and internal factors influence the shaping of a firm’s choice of mechanisms to govern transactions along the supply chain. Building from the existing literature, this paper proposes a conceptual model with two dimensions. The dimension of determinants includes three components: institution environment, industry structure and transaction characteristics. The dimension of governance patterns consists of five mechanisms a firm may use to govern its economic transactions along the supply chain: market contract, production contract, relational contract, relational production contract, and hierarchy. The paper provides prescriptions for the firm’s choice among five supply chain governance patterns under different conditions of the above three components of determinants

Explicit simulation of bolted endplate composite beam-to-CFST column connections

This paper explores the use of an explicit solver available in ABAQUS/Explicit to simulate the behaviour of blind bolted endplate connections between composite beams and concrete-filled steel tubular (CFST) columns. Main aspects of the explicit analysis such as solution technique, blind bolt modelling, choice of element type and contact modelling are discussed and illustrated through the simulation of a large-scale test on the considered joint. The mass scaling option and smooth step amplitude are very effective tools to speed up the explicit simulation. Shell elements can be used in modelling the I-beam due to their computational efficiency and accuracy in capturing local buckling effects. With a proper control of the loading rate, the explicit analysis can provide accurate and efficient predictions of the quasi-static behaviour of the bolted endplate composite connections

Optimal scheduling of large-scale wind-hydro-thermal systems with fixed-head short-term model

© 2020 by the authors. In this paper, a Modified Adaptive Selection Cuckoo Search Algorithm (MASCSA) is proposed for solving the Optimal Scheduling of Wind-Hydro-Thermal (OSWHT) systems problem. The main objective of the problem is to minimize the total fuel cost for generating the electricity of thermal power plants, where energy from hydropower plants and wind turbines is exploited absolutely. The fixed-head short-term model is taken into account, by supposing that the water head is constant during the operation time, while reservoir volume and water balance are constrained over the scheduled time period. The proposed MASCSA is compared to other implemented cuckoo search algorithms, such as the conventional Cuckoo Search Algorithm (CSA) and Snap-Drift Cuckoo Search Algorithm (SDCSA). Two large systems are used as study cases to test the real improvement of the proposed MASCSA over CSA and SDCSA. Among the two test systems, the wind-hydro-thermal system is a more complicated one, with two wind farms and four thermal power plants considering valve effects, and four hydropower plants scheduled in twenty-four one-hour intervals. The proposed MASCSA is more effective than CSA and SDCSA, since it can reach a higher success rate, better optimal solutions, and a faster convergence. The obtained results show that the proposed MASCSA is a very effective method for the hydrothermal system and wind-hydro-thermal systems

Non-destructive Characteristics of Ultrasonic Waves in 1018 Low Carbon Steel

In this paper, the dependences of the velocities and the absorption coefficients of ultrasonic waves transmitted in 1018 low carbon steel on temperature ranging from 0$^{\circ}$C to 50$^{\circ}$C were investigated. It was shown that the velocities of the ultrasonic longitudinal wave and ultrasonic shear wave were decreased when the temperature increased. The transportation of the ultrasonic longitudinal wave and ultrasonic shear wave depends on temperature and its coefficient in a temperature range of (0 - 50 $^{\circ}$C) was estimated about 0.8 m/s.$^{\circ}$C and 0.44~m/s.$^{\circ}$C, respectively. These obtained results are in good agreement with the theoretical prediction. Furthermore, the absorption coefficients of the ultrasonic longitudinal wave were also studied

An identification of the tolerable time-interleaved analog-to-digital converter timing mismatch level in high-speed orthogonal frequency division multiplexing systems

High-speed Terahertz communication systems has recently employed orthogonal frequency division multiplexing approach as it provides high spectral efficiency and avoids inter-symbol interference caused by dispersive channels. Such high-speed systems require extremely high-sampling time-interleaved analog-to-digital converters at the receiver. However, timing mismatch of time-interleaved analog-to-digital converters significantly causes system performance degradation. In this paper, to avoid such performance degradation induced by timing mismatch, we theoretically determine maximum tolerable mismatch levels for orthogonal frequency division multiplexing communication systems. To obtain these levels, we first propose an analytical method to derive the bit error rate formula for quadrature and pulse amplitude modulations in Rayleigh fading channels, assuming binary reflected gray code (BRGC) mapping. Further, from the derived bit error rate (BER) expressions, we reveal a threshold of timing mismatch level for which error floors produced by the mismatch will be smaller than a given BER. Simulation results demonstrate that if we preserve mismatch level smaller than 25% of this obtained threshold, the BER performance degradation is smaller than 0.5 dB as compared to the case without timing mismatch