Concatenation of polar codes with three‐dimensional parity check (3D‐PC) codes to improve error performance over fading channels

In this paper, we concatenated of three‐dimensional parity check (3D‐PC) block and polar codes for improving error correction performance and bit error rate (BER). Three different sizes of 3D parity check blocks (4 × 4 × 4, 8 × 8 × 8, and 16 × 16 × 16) are used for polar code concatenation. The 4 × 4 × 4 block returns the best performance, but higher complexity of decoder is needed unlikely. The 8 × 8 × 8 has returned acceptable complexity and good performacne. The complexity of decoder is less in the case of 16 × 16 × 16 with slight performance. The performance of the 3D‐PC is reduced when the codewords length is increased. The experiment considered the presence of additive white Gaussian noise (AWGN) with Rayleigh and Rician fading environments. 3D‐PC and polar code concatenation is more precise with codewords of short length, whereas there is insufficient concatenation accuracy with longer codewords. The outcomes of this study contain comparison between AWGN, Rayleigh, and Rician environments. The AWGN is noticed to have a lesser negative impact on the performance of code. Furthermore, increasing the code length may slightly fill the gap of performance between the concatenated and none concatenated polar codes due to the impact of code length on parity check code performance. Simulation results showed the coding performance in case of the polar code with concatenation and without concatenation for different code lengths. Generally, the 3D‐PC polar code concatenation is drawn the optimal result in AWGN environments.     

Robust Output Feedback Model Predictive Control: A Stochastic Approach

This paper addresses the robust explicit model predictive control scheme for linear systems with input and output constraint in the presence of disturbances and noise. Conditions for disturbance rejection are established by incorporating a full state/disturbance observer. The separation principle is applied to design an optimal observer in the unconstrained problem. Then, an efficient algorithm is developed to explicitly design observer gains by minimizing a quadratic performance criterion. It is shown that the solution includes a set of regions with piecewise affine functions of the state and reference vectors and a set of regions with optimal observers. In the proposed method, two sets of partitions associated with the control law and the observer gains are obtained. Therefore, the online computation includes finding the active regions of both observer and control law partitions in which the current state is located. The proposed technique is particularly attractive for a wide range of practical problems where the exact model of the actual system is not available.     

Stability analysis and design of nonlinear sampled‐data systems under aperiodic samplings

In this paper, the problem of exponential stability analysis and the design of sampled‐data nonlinear systems have been studied using a polytopic linear parameter‐varying approach. By means of modeling a new double‐layer polytopic formulation for nonlinear sampled‐data systems, a modified form of piecewise continuous Lyapunov‐Krasovskii functional is proposed. This approach provides less conservative robust exponential stability conditions by using Wirtinger's inequality in terms of linear matrix inequalities. The distances between the real continuous parameters of the plant and the measured parameters of the controller are modeled by convex sets, and the analysis/design conditions are given at the vertices of some hyper‐rectangles. In order to get tractable linear matrix inequality conditions for the stabilization problem, we performed relaxation by introducing a slack variable matrix. Under the new stability criteria, an approach is introduced to synthesize a sampled‐data polytopic linear parameter‐varying controller considering some constraints on the location of the closed‐loop poles in the presence of uncertainties on the varying parameters. It is shown that the proposed controller guarantees the exponential stability of the closed‐loop system for aperiodic sampling periods smaller than a known value, ie, maximum allowable sampling period. Finally, the effectiveness of the proposed approach is verified and compared with some state‐of‐the‐art existing approaches through numerical simulations.     

Production of ultrapure hydrogen via utilizing fluidization concept from coupling of methanol and benzene synthesis in a hydrogen-permselective membrane reactor

In this work, a novel fluidized-bed thermally coupled membrane reactor has been proposed for simultaneous hydrogen, methanol and benzene production. Methanol synthesis is carried out in exothermic side which is a fluidized-bed reactor and supplies the necessary heat for the endothermic side. Dehydrogenation of cyclohexane is carried out in endothermic side with hydrogen-permselective Pd/Ag membrane wall. Selective permeation of hydrogen through the membrane in endothermic side is achieved by co-current flow of sweep gas through the permeation side. A steady-state fixed-bed heterogeneous model for dehydrogenation reactor and two-phase theory in bubbling regime of fluidization for methanol synthesis reactor is used to model and simulate the integrated proposed system. This reactor configuration solves some observed drawbacks of new thermally coupled membrane reactor such as internal mass transfer limitations, pressure drop, radial gradient of concentration and temperature in both sides. The proposed model has been used to compare the performance of a fluidized-bed thermally coupled membrane reactor (FTCMR) with thermally coupled membrane reactor (TCMR) and conventional methanol reactor (CR) at identical process conditions. This comparison demonstrates that fluidizing the catalytic bed in the exothermic side of reactor caused a favorable temperature profile along the FTCMR. Furthermore, the simulation results represent 5.6% enhancement in the yield of hydrogen recovery in comparison with TCMR.     

Comparison of asphaltene structure and morphology under different deasphaltene methods

Problems associated with asphaltene deposition during the production, transportation, and processing of crude oils are some of the important issues in oil industry. Thus, accurate identification of structure and surface morphology of asphaltene should be investigated. In this study, asphaltene are isolated from an Iranian heavy crude oil under three different experimental conditions by using heat (thermal deasphaltene), heat and toluene (thermal-toluene deasphaltene), and n-heptane (n-heptane deasphaltene) as precipitation agent. The effect of isolation method on the crystallite structure and surface morphology of asphaltene is characterized by X-ray diffraction and scanning electron microscope technique, respectively. It is found that extraction procedure has a strong influence on the physicochemical properties of the isolated asphaltene. The results showed that at thermal deasphaltene solid such as micellar the shape was the dominant morphology of asphaltene particles that cause the least height of the crystallites and number of aromatic sheets in a stacked cluster. This morphology changes to semisolid smooth surface and agglomerated asphaltene with cavities by altering the separation method to thermal-toluene deasphaltene and n-heptane deasphaltene. The maximum heights of the crystallites belong to n-heptane deasphaltene.     

内在的和应力诱导产生的各向异性对颗粒土剪切波速的影响

本文研究了相对密度、平均有效应力、分级特性、固结应力比和样品制备过程中产生的初始组构各向异性对剪切波速度(Vs)的影响.结果表明,在给定的相对密度和有效约束应力下,处于各向异性压缩应力下的固结试样与各向同性或各向异性延伸应力状态下的固结试样相比,其剪切波速度更快.实验发现制备重组样品的沉积技术对剪切波速有重要影响,并对...     

Oxidation Properties of a Beta-Stabilized TiAl Alloy Modified by Rare Earth Elements

This paper explores the effects of adding rare earth elements (lanthanum or erbium) on the oxidation properties of Ti–43.5Al–4Nb–1Mo–0.1B (TNM) alloy. Isothermal oxidation tests were performed under air atmosphere at 900 and 1000 °C. Mass gain was measured in several steps during the oxidation test, and the oxidized specimens were characterized by XRD and FE-SEM. The results showed that while adding 0.1 at.% rare earth elements (REEs) reduced oxidation rate of the TNM alloy, 0.2 at.% REEs addition increased the mass gain of the alloys. The oxidation curves were fitted by a power-law equation; the results showed that the oxidation kinetic curves of all alloys obeyed parabolic growth kinetics (n = 2). Meanwhile, the activation energy of oxidation was in the range of 40–50 kCal/mol, thereby suggesting that the scale growth was controlled by mass transport in the TiO₂ layer. Also, the results of the scale characterization showed that addition of REEs at low level (e.g., 0.1 at.%) could reduce diffusion rate in the scale. However, addition of the higher amounts of La or Er (e.g., 0.2 at.%) due to the lower valency (+ 3) of these elements, as compared with Ti (+ 4), could lead to the increased anion diffusion, the formation of hillocks in the scale and a rise of the oxidation rate.     

An equivalent beam model for the analysis of tunnel-building interaction

The aim of this work is to study the effect of structural characteristics, including stiffness, geometry and weight on tunnel-adjacent structure interaction. Ground materials, tunnel geometry and excavator device are related to a part of metro tunnel of Tehran. To describe the ground behavior due to tunneling, a 3D FE code with an elastoplastic soil model was used. The adjacent building was modeled in two ways: one as an equivalent beam or shell and the other as a real geometry (3D frames). The obtained results from this theoretical work indicate particularly that the stiffness of adjacent structure controls the ground movement distribution induced by tunnel excavation which in agree with other researchers. As it was predicatively, increasing in structure weight leads to create the large displacement components in the ground. The structure width plays also a significant role in displacement distribution of ground. The comparison of the obtained results using two methods of structure modeling shows a very good conformity between them.     

A novel solution for simulating air overpressure resulting from blasting using an efficient cascaded forward neural network

Air overpressure (AOp) is a hazardous effect induced by the blasting method in surface mines. Therefore, it needs to be predicted to reduce the potential risk of damage. The aim of this study is to offer an efficient method to predict AOp using a cascaded forward neural network (CFNN) trained by Levenberg–Marquardt (LM) algorithm, called the CFNN-LM model. Additionally, a generalized regression neural network (GRNN) and extreme learning machine (ELM) were employed to demonstrate the accuracy level of the proposed CFNN-LM model. To conduct the CFNN-LM, GRNN, and ELM models, an extensive database, related to four quarry sites in Malaysia, was used including 62 sets of dependent and independent parameters. Next, the performances of the aforementioned models were checked and discussed through statistical criteria and efficient graphical tools. Finally, the results showed the superiority of CFNN-LM (R² = 0.9263 and RMSE = 3.0444) over GRNN (R² = 0.7787 and RMSE = 5.1211) and ELM (R² = 0.6984 and RMSE = 6.2537) models in terms of prediction accuracy. Furthermore, three different regression analysis metrics were used to perform the sensitivity analysis, and according to the obtained results, the maximum charge per delay (\(\beta\) = 0.475, SE = 0.115, t-test = 4.125) was considered as the most influential feature in modeling the AOp.