A novel open-loop high-speed CMOS sample-and-hold

A new open-loop high-speed CMOS sample-and-hold is presented. Based on new method for further reduction of voltage-dependent charge injection, a new CMOS sample-and-hold was designed. Simulation results confirm the effectiveness of this method. Over 10 dB improvement in signal-to-noise ratio, compared to the signal-to-noise ratio of conventional bottom plate sampling S/Hs was achieved with this method. A comparison between newly designed S/H and the bottom-plate sampling S/H is presented.     

Modification of glassy carbon electrode with multi-walled carbon nanotubes and iron(III)-porphyrin film: Application to chlorate, bromate and iodate detection

In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (k_s) of Fe(III)P immobilized on MWCNTs were 7.68 × 10⁻⁹ mol cm⁻² and 1.8 s⁻¹, respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO₃⁻, IO₃⁻ and BrO₃⁻ in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 × 10³, 7.4 × 10³ and 4.8 × 10² M⁻¹ s⁻¹, respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and bromate detections.     

An improved Differential Evolution algorithm using learning automata and population topologies

A new variant of Differential Evolution (DE), called ADE-Grid, is presented in this paper which adapts the mutation strategy, crossover rate (CR) and scale factor (F) during the run. In ADE-Grid, learning automata (LA), which are powerful decision making machines, are used to determine the proper value of the parameters CR and F, and the suitable strategy for the construction of a mutant vector for each individual, adaptively. The proposed automata based DE is able to maintain the diversity among the individuals and encourage them to move toward several promising areas of the search space as well as the best found position. Numerical experiments are conducted on a set of twenty four well-known benchmark functions and one real-world engineering problem. The performance comparison between ADE-Grid and other state-of-the-art DE variants indicates that ADE-Grid is a viable approach for optimization. The results also show that the proposed ADE-Grid improves the performance of DE in terms of both convergence speed and quality of final solution.     

Analysis of MTHFR and MTRR Gene Polymorphisms in Iranian Ventricular Septal Defect Subjects

Ventricular septal defect (VSD) is one of the most common types of congenital heart defects (CHD). There are vivid multifactorial causes for VSD in which both genetic and environmental risk factors are consequential in the development of CHD. Methionine synthase reductase (MTRR) and methylenetetrahydrofolate reductase (MTHFR) are two of the key regulatory enzymes involved in the metabolic pathway of homocysteine. Genes involved in homocysteine/folate metabolism may play an important role in CHDs. In this study; we determined the association of A66G and C524T polymorphisms of the MTRR gene and C677T polymorphism of the MTHFR gene in Iranian VSD subjects. A total of 123 children with VSDs and 125 healthy children were included in this study. Genomic DNA was extracted from the buccal cells of all the subjects. The restriction fragment length polymorphism polymerase chain reaction (PCR-RFLP) method was carried out to amplify the A66G and C524T polymorphism of MTRR and C677T polymorphism of MTHFR genes digested with Hinf1, Xho1 and Nde1 enzymes, respectively. The genotype frequencies of CC, CT and TT of MTRR gene among the studied cases were 43.1%, 40.7% and 16.3%, respectively, compared to 52.8%, 43.2% and 4.0%, respectively among the controls. For the MTRR A66G gene polymorphism, the genotypes frequencies of AA, AG and GG among the cases were 33.3%, 43.9% and 22.8%, respectively, while the frequencies were 49.6%, 42.4% and 8.0%, respectively, among control subjects. The frequencies for CC and CT genotypes of the MTHFR gene were 51.2% and 48.8%, respectively, in VSD patients compared to 56.8% and 43.2% respectively, in control subjects. Apart from MTHFR C677T polymorphism, significant differences were noticed (p < 0.05) in C524T and A66G polymorphisms of the MTRR gene between cases and control subjects.     

Hydrogen peroxide sensor based on riboflavin immobilized at the nickel oxide nanoparticle-modified glassy carbon electrode

A simple and sensitive electrochemical sensor based on nickel oxide nanoparticles/riboflavin-modified glassy carbon (NiONPs/RF/GC) electrode was constructed and utilized to determine H₂O₂. By immersing the NiONPs/GC-modified electrode into riboflavin (RF) solution for a short period of time (5–300 s), a thin film of the proposed molecule was immobilized onto the electrode surface. The modified electrode showed stable and a well-defined redox couples at a wide pH range (2–10), with surface-confined characteristics. Experimental results revealed that RF was adsorbed on the surface of NiONPs, and in comparison with usual methods for the immobilization of RF, such as electropolymerization, the electrochemical reversibility and stability of this modified electrode has been improved. The surface coverage and heterogeneous electron transfer rate constants (k _s) of RF immobilized on a NiO _x –GC electrode were approximately 4.83 × 10^?11 mol cm^?2, 54 s^?1, respectively. The sensor exhibits a powerful electrocatalytic activity for the reduction of H₂O₂. The detection limit, sensitivity and catalytic rate constant (k _cat) of the modified electrode toward H₂O₂ were 85 nM, 24 nA μM^?1 and 7.3 (±0.2) × 10³ M^?1 s^?1, respectively, at linear concentration rang up to 3.0 mM. The reproducibility of the sensor was investigated in 10 μM H₂O₂ by amperometry, the value obtained being 2.5 % (n = 10). Furthermore, the fabricated H₂O₂ chemical sensor exhibited an excellent stability, remarkable catalytic activity and reproducibility.     

Antioxidants and antiradicals in almond hull and shell (Amygdalus communis L.) as a function of genotype

To compare the antioxidant and antiradical activity of Amygdalus communis L. hulls and shells phenolic extracts in different genotypes, 18 A. communis L. genotypes were selected from those in Qooshchi, Qalgachi, Qovarchin Qale, Najaf Abad, Jamal Abad, Kahriz, Sfahlan of West and East Azerbayjan provinces of Iran in 2007. The fruits of these almonds were collected, their hulls and shells dried, ground and then methanolic extracts prepared from these hulls and shells. Total phenolic content was determined using the Folin–Ciocalteu (F–C) method. The extracts’ reducing power and scavenging capacity for radical nitrite, hydrogen peroxide and superoxide were evaluated. Significant differences were found in phenolic content of hulls and shells among various genotypes, radical scavenging capacity percentage varied significantly among genotypes and their hulls and shells. S₃-7 genotype with the highest phenolic content and antioxidant activity in its hulls represents a valuable genotype for procuring antioxidant phenolic compounds.     

Preparation, characterization and application of advanced isoconversional kinetics to epoxy/1,4-Bis(3-aminopropoxy) butane/MWCNT nanocomposite

A novel nanocomposite consisting bisphenol A diglycidyl ether/1,4-Bis(3-aminopropoxy) butane (1,4-APB)/multiwall carbon nanotube (MWCNT) was synthesized and characterized. Kinetics of the reaction was described by applying differential scanning calorimetry (DSC) data to isoconversional methods of Flynn-Wall-Ozawa (FWO), advanced isoconversional method of Vyazovkin, and non-linear integral isoconversional algorithm (NLN). It was found that at the presence of MWCNT the thermal decomposition temperature increased by rising the curing temperature and time. Data from dynamic mechanical thermal analysis (DMTA) showed that the glass transition temperature of the cured nanocomposite is 7 °C higher than that value found for the system without carbon nanotube. Scanning electron microscopy (SEM) was used to observe the fracture surface morphology and results indicated evidence of the interfacial interaction improvement and adhesion strength due to good dispersion of MWCNT.     

A Comprehensive Overview on the Latest Progress in the Additive Manufacturing of Metal Matrix Composites: Potential,Challenges, and Feasible Solutions

Nowadays, as an emerging technology, additive manufacturing(AM) has received numerous attentions from researchers around the world. The method comprises layer-by-layer manufacturing of products according to the 3D CAD models of the objects. Among other things, AM is capable of producing metal matrix composites(MMCs). Hence, plenty of works in the literature are dedicated to developing different types of MMCs through AM processes. Hence, this paper provides a comprehensive overview on the latest research that has been carried out on the development of the powder-based AM manufactured MMCs from a scientific and technological viewpoint, aimed at highlighting the opportunities and challenges of this innovative manufacturing process. For instance, it is documented that AM is not only able to resolve the reinforcement/matrix bonding issues usually faced with during conventional manufacturing of MMCs, but also it is capable of producing functionally graded composites and geometrically complex objects. Furthermore, it provides the opportunity for a uniform distribution of the reinforcing phase in the metallic matrix and is able to produce composites using refractory metals thanks to the local heat source employed in the method. Despite the aforementioned advantages, there are still some challenges needing more attention from the researchers. Rapid cooling nature of the process, significantly different coe fficient of expansion of the matrix and reinforcement, processability, and the lack of suitable parameters and standards for the production of defect-free AM MMCs seem to be among the most important issues to deal with in future works.     

Variance‐based global sensitivity analysis for fuzzy random structural systems

There have been increasing advances in the sophisticated approaches like fuzzy randomness to handle different uncertainties in civil engineering; however, less attention has been paid to the formulation of a sensitivity analysis for fuzzy random structural systems. In this study, the main objective is to present the formulation of fuzzy Sobol sensitivity indices to quantify the influence of fuzzy random structural parameters. Meanwhile, uncertainty in derivation of limit states and acceptance criteria in collapse analysis is addressed briefly and treated using fuzzy model parameters. To show the application of the established sensitivity test, the collapse behavior of a steel moment frame subjected to sudden column removal is evaluated thoroughly. The proposed fuzzy sensitivity indices are determined for the problem and the overall influence of fuzzy acceptance criteria on the collapse assessment is shown using fragility analysis. The results show that the presented fuzzy sensitivity analysis can give detailed insight into the characteristics of fuzzy random systems, and the epistemic uncertainty in derivation of limit states can have significant effects on the reliability‐based collapse analysis. It is worth mentioning that to alleviate high computational demands in fuzzy probabilistic collapse analysis, a neural network metamodel is applied in conjunction with the genetic algorithm which is also of practical value to engineers and researchers.     

Statistical optimization of experimental parameters for synthesis of manganese carbonate and manganese oxide nanoparticles

Taguchi robust design was used for optimization of direct precipitation reaction conditions in order to simple and fast synthesis of manganese carbonate nanoparticles. Manganese carbonate nanoparticles were synthesized in this study by addition of manganese ion solution to the aqueous carbonate reagent. Effects of several reaction variables, such as manganese and carbonate concentrations, flow rate of reagent addition and temperature on particle size of prepared manganese carbonate were investigated. The significance of these parameters in tuning the size of manganese carbonate particles was quantitatively evaluated by analysis of variance. The results showed that manganese concentration and carbonate concentration in the solutions and also flow rate have significant effects in preparation of manganese carbonate nanoparticles. Also, optimum conditions for synthesis of manganese carbonate nanoparticles via precipitation reaction were proposed. Analysis of variance showed that under the optimum condition, the size of manganese carbonate nanoparticles will be about 54 ± 12 nm. In another part of this study, solid state thermal decomposition reaction of precursor was used for preparation of Mn₂O₃ nanoparticles. The results showed that Mn₂O₃ nanoparticles synthesized via thermal decomposition of manganese carbonate nanoparticles have average size of 90 nm.