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In this paper, some applications of the Method of Least Squares (MLS) for the solution of various problems in electromagnetics engineering is briefly reviewed. Here, MLS is employed for the solution of various problems such as solution of equations, curve fitting to measured data, generalized Fourier coefficients, linear operator equations, inegro-differential equations, electrostatics and magnetostatics problems, boundary value problems (by the Least Square Boundary Residual Method LSBRM), design of impedance transformers and matching by step and tapered lines, optimum design of multihole directional couplers, coupled-line couplers, branch line couplers, ring couplers, analysis of wire antennas, antenna pattern synthesis, array synthesis and scattering. In this study, it becomes clear that MLS can be applied to devise effective numerical algorithms for the analysis and design of problems in the subject areas of radiation, scattering, antennas, microwaves, engineering mathematic, etc. Some papers and books published in the area of MLS applications for the analysis and design of problems in electromagnetics engineering are grouped and presented in references.

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In this study the combined effect of ultrasound and heat on inactivation of pectin methylesterase (PME) in fresh orange juice was investigated. To this end fresh orange juice was sonicated at 50, 60, 70 and 80 °C for 10, 15, 20, 25, and 30 minutes at various acoustic amplitudes and constant frequency of 30 kHz and the residual activity of PME was then measured. The results showed that ultrasound had a synergistic effect on heat resulting in an increase in the inactivation of PME. However, calculation of kinetic parameters and reaction constants indicated that increasing temperature decreased cavitation intensity and hence contribution of ultrasonic waves to PME inactivation. On the other hand, the acoustic amplitude level was found to initially increase and then diminish the rate of enzyme inactivation. In this article these changes are explained by activation parameters of DS^# and DH^#  and possible mechanisms for ultrasonic inactivation of PME are discussed.

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Background: In this study, data were collected from the Eastern Democratic Republic of Congo and analyzed by Cox regression model. In addition, hazard functions and survival outcomes in COVID-19 patients were also analyzed.
Materials & Methods: One million simulated data on hospitalized patients’ characteristics with positive SARS-CoV-2 infection were collected from the Humanitarian Data Exchange Source in the Eastern Democratic Republic of Congo from December 2020 to June 2021. Several statistical techniques were developed in this study for data analysis, including Kaplan-Meier curves, log-rank test, Schoenfeld residual diagnostics, and likelihood ratio test.
Findings: This study finding showed that there was a 4.5% increase in the expected hazard per unit year increase in age. In addition, the risk of death was higher in males than in females, and patients with no signs of anorexia, ageusia, or anosmia, no history of diabetes or tuberculosis, normal pulse rates, and no hypoxemia had a greater survival rate than those with such health conditions.
Conclusion: This study finding revealed that covariates such as age, gender, anorexia, ageusia, anosmia, diabetes, and tuberculosis were expressively connected with higher mortality rates. In addition, hypoxemia and high pulse rate were associated with higher death rates; however, anti-inflammatory and anticoagulant agents were shown to reduce mortality rates, and multivitamin or vitamin C had a substantial impact on patient survival.

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Residual stress measurement is one of the most interesting research areas in experimental mechanics. Residual stress is introduced to material due to plastic deformation of parts and can be one of the most effective parameters on design and operation of parts. ASTM E837-01 standard studies residual stress determination in parts by hole drilling method and represent calibration coefficients for flat sheets with constant stress profile. However, there is no certain standard on the residual stress measurement by Incremental Hole Drilling Method (IHDM) which is the subject of this study. IHDM can obtain stress profile by using two modified stress calibration coefficients. In this article, the stress calibration coefficients have been extracted for incremental hole drilling by using finite element analysis (FEA). FEA contains both biaxial tension test and pure shear test which a hole has been drilled step by step in the parts by removing elements and the strains changes were determined at three strain gauge positions on the surface. At last, the calibration coefficients are determined for each step and the accuracy of coefficients have been verified by a set of experimental test and a FE analysis. The experimental test contains four-point bending of an AA5056 flat aluminum sheet. The numerical analysis contains four-point bending of a flat sheet. In both cases, the stress profile can be determined easily by using analytical equations. Average analytical stress in each increment has been calculated and compared with the result of numerical incremental hole drilling method. The comparisons show that numerical and experimental results have no significant differences in first six steps but in the last four steps show an increasing errors due to the change in stress profile and hole geometry. Results presents that the calibration coefficients have suitable accuracy in stress profile determination.

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In this research, a novel method to decrease macro-residual stresses of laminated composites by adding carbon nano-fiber (CNF) is proposed. To this end, using micromechanical and modified micromechanical approaches, coefficient of thermal expansion (CTE) and Young’s modulus of carbon nano-fiber reinforced polymer are calculated. Then using this enhanced matrix, longitudinal and transverse of thermal expansion and Young’s modulus of a CNF/glass/epoxy unidirectional lamina in presence of CNF are obtained. Finally, using the classical lamination theory (CLT), macro-residual stresses for CNF/glass/epoxy laminated composites are obtained. The results explain how CNF can result in reducing macro-residual stresses in nano particle filled laminated composites. The results for both cross ply and angle ply glass/epoxy laminated composites are presented and show that adding CNF through the matrix can decrease macro-residual stresses in each plies up to about 30%. The main reason for the decrease in residual stresses are due to the sever decrease of coefficient of thermal expansion of the unidirectional ply.

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Microbial quality of potable water is of the most import guidelines of the World Health Organization (WHO). One of the main concerns of water supply and distribution network problems particularly in large cities is microbial growth in the pipelines that are significant non-compliers and repeatedly detect bacteria in finished drinking-water. In Iran, chlorine is mostly used as disinfection agent in conventional chemical treatment process in water treatment plants for supplying safe drinking water. This is done to maintain a residual concentration within a water distribution system for preventing the growth of pathogenic bacteria. Therefore, to meet water quality standards, it is necessary to maintain free chlorine residuals throughout the minimum and maximum levels for various reasons. This study was conducted to examine the relationship between residual chlorine concentration, turbidity and microbial quality of water used for drinking in water distribution system of city of Semnan. Heterotrophic Plate Count (HPC) bacteria was used as an indicator for microbial quality and residual chloride concentration and turbidity were selected as the main parameters for determining correlation. In this research, for the first time Water-Gems as a comprehensive and easy-to-use water distribution modeling application bacteriological software with GIS system was employed as a tool to evaluate the microbial water quality in the network of Semnan city which is known as drawn area with limited water resources. Water-Gems is a multi-platform hydraulic and water quality modeling solution for water distribution systems with advanced interoperability, geospatial model-building, optimization, and asset management tools. For the study, all required information from water supply system such as topographical references, type and diameter of pipelines, pressure head in the system and connections were imported in the software. Then sampling points were selected and 25200 samples were made for turbidity, residual chloride concentration and HPC bacteria. The results indicated that there is high correlation between free chloride residual, turbidity and HPC which means that lower chloride concentration caused the increase in turbidity and HPC number. This information can be used to formulate a bacterial growth control strategy.

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In this paper, a unit cell based micromechanical model is presented to predict the elastic-viscoplastic response of aligned short fiber titanium matrix composites subjected to combined axial loading in the presence of fiber/matrix interfacial damage. The effects of manufacturing process thermal Residual Stress (RS) are also included in the analysis. The representative volume element (RVE) of the short fiber composites consists of c×r×h cells in three dimensions in which a quarter of the short fiber is surrounded by matrix sub-cells. In order to obtain elastic-viscoplastic curves, the fiber is assumed to be linear elastic, while the matrix exhibits elastic-viscoplastic behavior. The Evolving Compliance Interface (ECI) model is employed to analysis interface damage. This model allows debonding to progress via unloading of interfacial stresses even as global loading of the composite continues. Results revealed that for more realistic predictions, in comparison with available experimental and the other models results, both interfacial damage and thermal residual stress effects should be considered in the analysis.

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Field experiments were conducted to evaluate the effect of thiobencarb and oxadiargyl herbicides on rice (Oryza sativa L.) and their possible residual effects on spinach (Spinacea oleracea L.) and lettuce (Lactuca sativa L.) at Dashtnaz and Gharakhil Agricultural Research Stations, Iran. Treatments included thiobencarb at 3.16 and 6.33 kg a.i. ha-1, oxadiargyl at 0.15 and 0.30 kg a.i. ha-1 and a non-treated control. After harvesting rice, trial plots were kept undisturbed until late September when spinach was seeded in half of each plot. In November lettuce was transplanted in another half of the plots. Soil residual oxadiargyl at 0.30 kg a.i. ha-1 stunted rice up to 31%, but this injury was transient and did not reduce yield. The adverse effect of oxadiargyl on rice was lower at Gharakhil possibly due to the greater binding by soil organic matter (OM). At Dashtnaz, spinach fresh yield was significantly affected by soil residues of oxadiargyl. Whereas lettuce fresh yield was significantly reduced in both thiobencarb and oxadiargyl treated plots. At Gharakhil, fresh yield of lettuce was not affected significantly. The experimental results revealed that soil characteristics, in particular OM content, are the main factors controlling the effect of thiobencarb and oxadiargyl residues. Furthermore, it could be concluded that oxadiargyl affected rice and spinach fresh yield greater than thiobencarb. Since no statistically significant differences were found in rice, spinach, and lettuce yield between the two applied doses of thiobencarb, from economical and environmental point of view, the lower thiobencarb dose is recommended to be used in paddy fields of northern Iran.

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In this paper, annealing processes for stress relaxation and removing residual stresses from polycarbonate sheet are studied and evaluated using experimental tests. Then, by making some alterations and modifications in the previous heating cycles thermal operations are performed on different samples in a try and error process. Appraising the obtained results, a modified thermal cycle is presented which can remove the residual stress from the polycarbonate sample, while reducing the time and cost of the annealing process. According to this process, the temperature is raised to 100˚C at the heating rate of 20˚C/h. The samples are kept at this temperature for 3 hours and then, the heating is continued up to 140˚C at a slower rate of 5˚C/h. Then, the specimens are heated at the rate of 1˚C/h until maximum temperature of Tmax = 156˚C. After reaching this point, the samples are cooled immediately, and the cooling rates are same as the heating rates.

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Abstract: Wire electrical discharge machining (wire-EDM) has a significant position among production technologies mainly due to its capacity of machining hard materials and intricate shapes. One of the major problems with this process is the error in cutting corners. Processing forces acting on the wire and low rigidity of the wire are responsible for wire deformation, which has a direct influence on the accuracy of the corner cutting. In this research, investigation is focused on the convex corner radii errors and alternative solutions are proposed for the case of successive cuts (one roughing and two finishings). Experiments are carried out for roughing operation by considering frequency of discharges and feed speed. The residual materials on straight and curved paths are the output parameters. Results indicate that optimization of these parameters have a better influence for control of residual material thickness on straight paths than on curved corners. One important conclusion is that roughing is the most influential stage of cutting by WEDM. Then, concave corner radii produced during successive cuts, the effect of corner angle and corner radii are investigated. Errors at radii of different corner angles are identified and related to arc length and residual material thickness in the curved corner. Finally, an effective approach is presented for improving the accuracy of the small-radius concave corner radii of finishing stage. The main conclusion is that to achieve accurate corner radii, one must increase the traversed corner arc length by wire in the small-radius concave corner radii.

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Drilling of composite materials is one of the major processes in the manufacturing and assembly of sub-component. However, drilling of composite laminates can cause several damages such as degradation in residual tensile strength. In this study, effects of cutting speed, feed rate and drill angle on residual tensile strength of drilled laminates has been investigated. For this purpose, the Taguchi method was employed for three factors at three levels. Acoustic emission signals and wavelet analysis are used to monitor residual tensile strength. The experimental results indicated that the feed rate has the most significant effect. Based on time-frequency analysis of AE signals, it was found that AE signals with frequency ranges of (62.5-125), (250-312.5) and (312.5-375) KHz were generated from matrix cracking, fiber slipping and fiber breakage respectively.

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Dyes are being extensively used in textile, dyeing and leather industries and usually have a synthetic origin and complex chemical structure that may be mutagenic and carcinogenic. Among various processes of dye removal from wastewater, adsorption is considered to be the most efficient process. Activated carbon is the most widely used adsorbent with great success because of its high adsorption capacity, but its use is limited due to its high-cost, has led to a search for cheaper substitutes. Optimization methods, such as the Taguchi method has been generally adopted to optimize the design parameters, because this systematic approach can significantly minimize the overall testing and the experimental costs. In this study; the optimum condition of Reactive Blue 19(RB19) removal by activated carbon based on pomegranate residual is determined using Taguchi method. For this purpose, 4 main factors such as pH, adsorbent dose, initial dye concentration and contact time were considered in 5 levels. Therefore, an L25 orthogonal array was chosen, and the experimental conditions were obtained. In addition, after design of experiments, an analysis of the signal-to-noise (S/N) ratio was needed to evaluate the experimental results. The analysis of mean (ANOM) statistical approach was adopted herein to construct the optimal conditions. In addition to ANOM, the analysis of variance (ANOVA) statistical method was also used to analyze the influence of each controllable factor on the dye removal efficiency. To prepare the To prepare the activated carbon (AC), pomegranate residual was collected. Collected sample has been dried in an oven for 2 h at 100 0C. It was then ground in a ball mill and the material passed through the No.30 mesh was collected and tested. They were soaked for 24 h in a 1:1 wt. ratio with 50 wt. % phosphoric acid as the carbonized at room temperature. The sample is then decanted and dried in a muffle furnace for 1 h at 500 0C. They were then washed sequentially several times with hot distilled water, until pH of the washing solution became neutral. AC was finally powdered and sieved by the No. 100 mesh. The experiments were done 3 times according to the tests conditions determined by the Taguchi method and the dye removal efficiency was measured. Due to the results of S/N and ANOM, it can be inferred that the optimum mixture proportions to obtain the highest RB19 removal efficiency are as follows. (1) Initial dye concentration of 100 mg/L; (2) pH of 11; (3) adsorbent dose of 1.75 gr/L; and (4) contact time of 7 minutes. The experiment with aforementioned condition was done and result was shown the highest efficiency (98.94%). According to the result of ANOVA, the rank order of the contribution percentage of each factor on RB19 removal efficiency is as follows: (1) initial dye concentration (52.67%), (2) adsorbent dose (33.32%), (3) pH (13.61%), and (4) contact time (2.72%).

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This paper deals with the design of an unknown input observer (UIO) with the assumption that the well-known observer matching condition is not satisfied. The proposed method can be used for fault detection problems with the use of residual vector. The basis of method is to compensate the unmatched uncertainties with the use of a set of auxiliary outputs. The introduced auxiliary outputs are obtained from successive integration of the system measurements and known inputs. Then, an unknown input observer is proposed which estimates exponentially the outputs. Therefore, the residual vector, generated from the estimated outputs and the actual outputs, will be obtained which insensitive to the unmatched disturbances. At the same time, the sensitivity of the proposed residual vector to the fault in sensors is investigated. The generated residual vector will be more robust against the presence of noise in the measurements. It is shown through numerical simulations that the proposed residual vector is sensitive to the presence of fault in sensors while it is insensitive to the presence of the unknown input. In addition, a comparison with a derivative based method is presented.

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Multi-pass welding process is one of the most applicative methods of welding in various industries. In this paper, temperature and residual stress distribution due to three pass welding of two plates made of AISI 321 stainless steel having different thicknesses is studied. Welding process consists of three welding passes of two Shielded Metal Arc Welding (SMAW) process and one Gas Tungsten Arc Welding (GTAW) process. First, the benchmark plates are manufactured and welding process is performed. The transient temperature distribution during the welding process is recorded using thermocouples attached to the welding plates. First this process simulated experimentally and temperature distribution during to welding process was measured using thermocouples. Furthermore, the final residual stress distribution after welding process is measured using incremental center hole drilling technique (ICHD). The three pass welding process was then simulated using ABAQUS finite element (FE) code. The finite element model consists of temperature-dependent properties of base metal and weld metal. Furthermore, moving heat source and the element-birth technique is implemented in FE model. Experimentally measured temperature and residual stresses provide an in-depth knowledge insight the complicated welding process. . Comparing between the results shows that the numerical predictions and experimental measurements have good agreement and therefore the FE developed model can be employed in designing and evaluating of welded structures.

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Nowadays, composite materials are used in different applications. Some of these applications involve components subject to cyclic loading. Fatigue is the dominant failure mechanism for structures under this type of loading. Hence, proper prediction of fatigue life is essential for safe design and operation of structures, maintenance, repair and replacement of components. Many of the existing models in this field have not assessed the degradation of material properties such as stiffness and strength during fatigue damage. In this paper, a stiffness-based model is initially evaluated for fatigue damage analysis of composite structures. The model is validated with two sets of experimental data. A residual strength model is coupled to the choice model and a modified model is developed. Then, residual fatigue life of fiber reinforced polymeric composites is predicted for three sets of experimental data under two-stage loading. The results demonstrate that the proposed model has an improvement on accuracy in the estimation of residual fatigue lives. For better evaluation of the developed model, experimental results and some existing models are compared with the present study predictions. It is concluded that in most cases, the predicted values by the proposed model is closer to experimental values in comparison with other models.

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In this study, experimental tests were performed to evaluate the effects of axisymmetric cylindrical projectile nose shapes and initial velocities on ballistic performance of laminated woven glass epoxy composites. Projectile initial velocity and nose sharpness changes, absorbed energy, delamination area, etc. are investigated by six blunt, hemispherical, conical and ogival projectiles. Hand lay-up method has been used to manufacture composite targets with 18 layers of 2D woven glass fibers of 45% fiber volume fraction. The epoxy system is made of epon 828 resin with jeffamine D400 as the curing agent. The results show that the maximum influence of projectile geometry on target behavior, occurs in ballistic limit area. In this range of initial velocity, ogival (CRH=2.5) and Blunt projectiles show the best and the worst ballistic performance. The delamination area decreases as the projectile nose sharpness increases or its initial velocity decreases. Ballistic curves for different projectiles show that the difference between projectiles behavior decreases in higher impact velocities. Because of target shear failure in blunt projectile impact, the amount of target absorbed energy for this projectile is less than other projectiles in higher impact velocities away from ballistic limit velocity.

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Residual stresses reduce life time of welded joints and change the welded structure formation. Residual stress is stresses that remain in the body some specific operation like welding and is available when body is not under external loads. Different methods are available for residual stress relieved in any welded samples. In this research, samples A, B and C have been prepared and welded. Stress of Samples A and B have been relieved using heat treatment method and ultrasonic method, respectively. Also, no operation has been taken on the sample c. for different amount of residual stress of each sample, hole drilling method used and amount of residual stress in welding heat affected area of each sample determined. Results show that residual stress in ultrasonic method is for less than heat treatment method. To validate the results the x-ray diffraction method was also used and results of this method show that sample with ultrasonic stress, stress reliving had no peek in 2Ө angles, but for sample with heat treatment stress reliving had a peek in 137° that shows some residual stress.

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Cold working a hole decreases tendency of fatigue crack near the hole to initiate or growth. It is due to creation some compressive tangential residual stresses around the hole. Determination of mentioned residual stresses with a non-destructive, simple and non-expensive method is the key step in design process of holed components. In this article, residual stresses have been determined by mounting some strain gages around the hole and in fact surface strains during cold working process have been introduced as a feature for residual stress field. Delineation the numbers of needed strain gages and also proper place for mounting them around the cold worked hole is the main object of this research. Results have a good agreement with test result of cold working on specimens made of Al2024. According to the results, mounting two strain gages at same radius in opposite side of hole edge; which one in radial and another in tangentially direction; is needed for determining the residual stress field. Also, strain gages should be mounted in elastic zone. Mounting the gages in plastic zone led to have errors and unreliable results.

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In this study, microstructure, microhardness and residual stress in the butt jointed friction stir welded aluminum alloy 2024-T351 plates with different tool’s rotational and traverse speed is studied. According to the 2024-T351 aluminum is a heat treatable alloy, Hardness test results showed that increasing rotational speed or decreasing traverse speed of the tool reduced hardness in the weld zone. Then, using standard X-ray diffraction, which is a non-destructive method, residual stress in the welded samples is determined. A thermal model of friction stir welding process is simulated by using finite element method in the ABAQUS software. Comparison of residual stress results that obtained from the numerical solution with experimental measurements show that, the numerical model can predict the residual stress fields in friction stir welding joints reasonably. The results show that, increasing rotational speed, cause to higher residual stress in the weld zone, due to generation the higher thermal gradient and also, The higher tool traverse speed will induce a greater high-stress zone with a higher stress value in the weld, because of, a lower heat input and result in the relatively harder metal in the weld zone, causes a greater resistance to the plastic extrusion.