An adaptive arm’s mechanical impedance estimator for rehabilitation robots without force and acceleration sensors

The mechanical impedance of the human arm can be measured to quantitatively assess the motor function. In this paper, an adaptive least square estimation method is proposed for online measurement of the mechanical impedance of the arm, without force or acceleration sensors, which extremely reduces the expenses and complexity of rehabilitation robots. The proposed strategy may also be used for monitoring the dynamic changes of the mechanical impedance. Estimation of time-varying force is also the other capability of the algorithm. The closed-loop stability of the system is analytically shown using the Lyapunov stability theorem. To show the applications of the proposed scheme, two main scenarios are described which can be used for the rehabilitation robots to assess the motor recovery of the patients undergoing the rehabilitation sessions. To validate the scheme, a 2-DOF manipulator is adopted to illustrate the accuracy of the impedance and force estimations in noiseless and noisy conditions.     

Determination of zinc(II) ions in waste water samples by a novel zinc sensor based on a new synthesized Schiff's base

A highly selective and sensitive zinc ion-selective membrane electrode based on N,N′-phenylenebis (salicylideaminato) (L) as a new carrier is reported. The membrane is composed of poly (vinyl chloride) (PVC), o-nitrophenyl octyl ether (NPOE) as plasticizer, potassium tetrakis(p-chlorophenyl) borate (KTpClPB) as lipophilic ionic additive, and L as sensing material. The proposed electrode displays a Nernstian response to Zn²⁺ ions over a wide concentration range of 5.0 × 10^? 7–1.0 × 10^? 1 M with the slope of 29.4 ± 0.2 mV per decade and a detection limit of 2.6 × 10^? 7 M. The sensor has a relatively fast response time of < 10 s and it can be used in the pH range of 3.0–7.0 for at least 2 months without any significant divergency in potential. The selectivity coefficients for mono-, di-, and trivalent cations indicate the good selectivity of sensor for Zn²⁺ ions over a large number of interfering cations. As a result the proposed electrode was applied to Zn²⁺ ions determination in mixture solutions and wastewater samples.     

A comparative study of the carbon dioxide and nitrogen minimum miscibility pressure determinations for an Iranian light oil sample

Miscible gas injection is an approved profitable process that could significantly enhance oil recovery from different types of reservoirs while the major factor affecting its efficiency would be the minimum miscibility pressure (MMP) value. A recent experimental technique, known as vanishing interfacial tension (VIT), can estimate the MMP for gas–oil mixtures by measuring interfacial tension values and extrapolating them to zero at a sequence of pressures. Compositional simulation models are also useful in MMP determination by tuning an equation of state to compute the realistic phase behavior of reservoir fluid. In this paper, the capability and quality of MMP prediction via different methods such as laboratory slim tube tests, VIT technique, compositional simulation, and various empirical correlations were examined using a light oil sample taken from an Iranian carbonate reservoir, employing two pure gases of CO₂ and N₂ as the injectants. The accuracy and validation of the mentioned methods were then confirmed successfully by obtaining negligible overall absolute deviation percentages (AD%) compared with the conducted slim tube tests results.     

A boundary-only meshless method for numerical solution of the Eikonal equation

The radial basis function (RBF) collocation methods for the numerical solution of partial differential equation have been popular in recent years because of their advantage. For instance, they are inherently meshless, integration free and highly accurate. In this article we study the RBF solution of Eikonal equation using boundary knot method and analog equation method. The boundary knot method (BKM) is a meshless boundary-type radial basis function collocation technique. In contrast with the method of fundamental solution (MFS), the BKM uses the non-singular general solution instead of the singular fundamental solution to obtain the homogeneous solution. Similar to MFS, the RBF is employed to approximate the particular solution via the dual reciprocity principle. In the current paper, we applied the idea of analog equation method (AEM). According to AEM, the nonlinear governing operator is replaced by an equivalent nonhomogeneous linear one with known fundamental solution and under the same boundary conditions. Finally numerical results and discussions are presented to show the validity and efficiency of the proposed method.     

Genetic and differential evolution algorithms for the allocation of customers to potential distribution centers in a fuzzy environment

In order to serve the customers' demands in a supply chain, one of the important decisions is to select some candidate places as distribution centers (DCs) in the network. For opening a potential DC and also shipping from the DC to the customers, there are two types of costs named fixed and variable costs, respectively. Contrary to previous work, we consider fuzzy costs and utilize differential evolution (DE) algorithm for the first time for the given problem. In addition, some new crossover and mutation operators are proposed in DE. We also address the problem with genetic algorithm (GA) and compare the results with the presented DE algorithm. In the both presented algorithms, Prüfer number representation is employed. Besides, the Taguchi experimental design method is employed to study the behavior of the parameters dealing with the problem. To evaluate the performance of proposed algorithms, various problem sizes are considered and the computational results are analyzed. Finally, the impact of the rise in the problem size on the performance of the algorithms is investigated. The DE depicts a superior performance over GA in all problem sizes.     

A Multi-Objective Optimization Approach for Joint Channel Assignment and Multicast Routing in Multi-Radio Multi-Channel Wireless Mesh Networks

Multicast routing is an effective mechanism for delivering data to a group of receivers. Due to intrinsic property of air medium in wireless mesh networks (WMN), interference is an important issue in determining the data rate for multicast services. Interference reduction is handled by assigning multiple orthogonal channels to multiple radios in multi-radio multi-channel WMNs. Channel assignment is known to be a NP-complete problem. Most prior methods have solved multicast routing and channel assignment problems sequentially and have not considered the interplay between these two problems. Focusing on this issue, we address joint channel assignment and routing problem for multicast applications. In this paper, a novel technique based on a multi-objective genetic algorithm is proposed to build a delay constrained minimum cost multicast tree with minimum interference. We have examined the proposed algorithm on different network configurations. Experimental results demonstrate that our method finds better trees in terms of cost, delay, and interference compared to prior methods.     

Probabilistic Failure Prediction for Deteriorating Pipelines: Nonparametric Approach

Component failures in water distribution systems are usually predicted by parametric models where the model parameters are determined by projecting the past failure rates of the component to the future. This paper shows that in such techniques, failures are implicitly assumed to be stationary random processes. However, due to the nonstationary nature of some influencing factors, this assumption may lead to inaccurate predictions. A new nonparametric technique is developed for failure prediction of classes of pipes considering this nonstationary process. The presented technique uses limited data that are typical to the databases of water distribution systems. In this method, maximum likelihood estimates of the probability of future failures are calculated and used, both to predict the number of failures occurring within a specified period of time in future, and to provide some lower and upper bounds (confidence intervals) for the estimations. This technique is applied to predict the failures of water pipes in western suburbs of Melbourne. Results of the predictions are compared with the empirical results from a failure record. Deviation of these predictions from empirical measures in terms of both rejection rates and mean-square errors of predictions are acceptable.     

Electron Microscopy Study of γ-Al2O3 Supported Cobalt Fischer–Tropsch Synthesis Catalysts

Three supported catalysts containing 20 wt% cobalt and 0.5 wt% rhenium were subjected to electron microscopy studies in their calcined state. The catalysts were prepared by incipient wetness impregnation of γ-Al₂O₃ supports of different pore characteristics with aqueous solutions of cobalt nitrate hexahydrate and perrhenic acid. The influence of the support on the Co₃O₄ crystallite size and distribution was studied by X-ray diffraction and electron microscopy. There was a positive correlation between the pore diameter of the support and the post calcination Co₃O₄ crystallite size. On all three γ-Al₂O₃ supports, Co₃O₄ was present as aggregates of many crystallites (20–270 nm in size). Cobalt oxide did not crystallise as independent crystallites, but as an interconnected network, with a roughly common crystallographic orientation, within the matrix pore structure. The internal variations in crystallite size between the catalysts were maintained after reduction. Fischer–Tropsch synthesis was carried out in a fixed-bed reactor at industrial conditions (T = 483 K, P = 20 bar, H₂/CO = 2.1). Although the cobalt-time yields varied significantly (4.6–6.7 × 10^?3 mol CO/mol Co s), the site-time yields were constant (63–68 × 10^?3 s^?1) for the three samples. The C₅₊ selectivity could not be correlated to the cobalt oxide aggregate size and is more likely related to the cobalt particle size and chemical properties of the γ-Al₂O₃ support.     

Improvement of Structural and Mechanical Properties of Al-1100 Alloy via Friction Stir Processing

In the present study, the relationship between structural and mechanical properties of friction stir processed Al-1100 alloy and process parameters (tool rotation rate: ω and traverse speed: ν) was studied to get an better understanding and optimizing the friction stir processing (FSP) condition of this alloy. Microstructural studies revealed that increasing of ω up to 720 rpm resulted in grain refinement in the stirred zone (SZ), but higher increasing of ω caused grain growth in this zone. These variations of SZ grain size illustrated that the prevailing factor that determined the SZ grain size was plastic deformation at first and thereafter, peak temperature in the SZ. Mechanical properties investigations were in accordance with microstructural findings and illustrated that optimized FSP condition for Al-1100 alloy was 720 rpm and 20 mm/min. Optimized FSP condition resulted in a significant improvement of tensile strength and elongation up to 22 and 8% of those of base metal, respectively.     

Biological evaluation of polyvinyl alcohol hydrogel crosslinked by polyurethane chain for cartilage tissue engineering in rabbit model

Polyvinyl alcohol (PVA) hydrogel chains were crosslinked by urethane pre-polymer (PPU) in order to fabricate a new substitute for cartilage lesions. The microscopy images showed that the cultured chondrocytes had spherical morphology on PVA–PPU sample after 4 weeks of isolation in vitro. The alcian blue and safranin O staining proved the presence of proteoglycan on the surface of PVA–PPU sample secreted by cultured chondrocytes. This was confirmed by the detection of sulfate ions in the wavelength dispersive X-ray (WDX) analysis. In addition, the expression of collagen type II and aggrecan were observed in chondrocytes cultured on PVA–PPU by RT-PCR. Moreover, the implantation of the PVA–PPU sample with autologous cultured chondrocytes revealed the formation of neocartilage tissue in a rabbit model during 12 weeks follow up. In conclusion, the results verified that isolated chondrocytes cultured on PVA–PPU retain their original phenotype and this composition can be considered as promising substrate for cartilage tissue engineering.