On the Positive Effect of Delay on the Rate of Convergence of a Class of Linear Time-Delayed Systems

This paper is a comprehensive study of a long observed phenomenon of increase in the stability margin and so the rate of convergence of a class of linear systems due to time delay. We use Lambert W function to determine (a) in what systems the delay can lead to increase in the rate of convergence, (b) the exact range of time delay for which the rate of convergence is greater than that of the delay free system, and (c) an estimate on the value of the delay that leads to the maximum rate of convergence. For the special case when the system matrix eigenvalues are all negative real numbers, we expand our results to show that the rate of convergence in the presence of delay depends only on the eigenvalues with minimum and maximum real parts. Moreover, we determine the exact value of the maximum rate of convergence and the corresponding maximizing time delay. We demonstrate our results through a numerical example on the practical application in accelerating an agreement algorithm for networked~systems by use of a delayed feedback

On Robustness Analysis of a Dynamic Average Consensus Algorithm to Communication Delay

This paper studies the robustness of a dynamic average consensus algorithm to communication delay over strongly connected and weight-balanced (SCWB) digraphs. Under delay-free communication, the algorithm of interest achieves a practical asymptotic tracking of the dynamic average of the time-varying agents' reference signals. For this algorithm, in both its continuous-time and discrete-time implementations, we characterize the admissible communication delay range and study the effect of the delay on the rate of convergence and the tracking error bound. Our study also includes establishing a relationship between the admissible delay bound and the maximum degree of the SCWB digraphs. We also show that for delays in the admissible bound, for static signals the algorithms achieve perfect tracking. Moreover, when the interaction topology is a connected undirected graph, we show that the discrete-time implementation is guaranteed to tolerate at least one step delay. Simulations demonstrate our results

Study of the Effective Parameters on Selective Catalytic Reduction of NOx by Ammonia over a Vanadia-Titania Catalyst from Exhaust Gases

The removal of nitrogen oxides (NOx) is crucial problem for global environment. In This study, a 3D dynamic simulation model for the application in investigation of the reaction characteristic and the phenomena of transport in the catalytic filter of the SCR reactor is introduced. In order to make an assessment on the kinetic parameters of the model by the mechanism of Eley-Ridel (ER) from experimental data, an optimization method which acts by integrating the Taguchi method, a real-coded genetic algorithm auxiliary model is proposed. With the aid of the introduced dynamic model, the impacts of the key parameters, namely operating temperature, the gas hourly space velocity, the amount of the applied ammonium and the cross section of the channel of SCR reactor on the NOx conversion and NH3 slip phenomena were investigated. By comparing with the experimental data available in the literature, it was validated and it is found that NOX conversion increases with the decrease in the operation temperature, the space velocity, the concentration of H2O, the ratio of NH3/NOX, and the increase in O2 concentration. Moreover, it is evident that the reactors with the square shaped cross section have more percentage of conversion but the resident time in the corner increased

Numerical solution for the systems of variable-coefficient coupled Burgers’ equation by two-dimensional Legendre wavelets method

In this paper, a numerical method for solving the systems of variable-coefficient coupled Burgers’ equation is proposed. The method is based on two-dimensional Legendre wavelets. Two-dimensional operational matrices of integration are introduced and then employed to find a solution to the systems of variable-coefficient coupled Burgers’ equation. Two examples are presented to illustrate the capability of the method. It is shown that the numerical results are in good agreement with the exact solutions for each problem

Characterization of Some Novel Nitro-Schiff Bases and Their Complexes of Nickel(II) and Copper(II)

Synthesis and characterization of some new Schiff base ligands derived from various diamines and nitrosalicylaldehyde and their complexes of Ni(II) and Cu(II) are reported. Several spectral techniques such as UV-Vis, FT-IR, and NMR spectra were used to identify the chemical structures of the reported ligands and their complexes. e ligands are found to be bound to the metal atom through the oxygen atoms of the hydroxyl groups and nitrogen atoms of imine groups, which is also supported by spectroscopic techniques. e results obtained by FT-IR and NMR showed that the Schiff base complexes of transition metal (II) have squareplanar geometry

Efficient One-Pot Synthesis of 1,4-Dihydropyridines Catalyzed by Magnetic MnFe2O4 Nanoparticles

The efficient one-pot synthesis of some 1,4-dihydropyridines is described by a condensation reaction of some aldehyde derivatives, ethyl acetoacetate and ammonium acetate in the presence of superparamagnetic manganese ferrite nanoparticles at 80 °C. The advantages of this protocol include selectivity, high purity of the products, excellent yields, short reaction times, ease of processing, and environmentally friendly conditions for the synthesis of 1,4-dihydropyridines. In addition, the catalyst can be recovered and reused in multiple runs without significantly reducing the product yield

Editorial – Eye Disorders in the Post-COVID Era

This is an Editorial and does not have an abstract. Please download the PDF or view the article HTML

Ziv-aflibercept in Diabetic Macular Edema: Relation of Subfoveal Choroidal Thickness with Visual and Anatomical Outcomes

Purpose: To evaluate the effects of intravitreal ziv-aflibercept injections (IVZ) on subfoveal choroidal thickness (SCT) as well as on central macular thickness (CMT) and on best corrected visual acuity (BCVA) changes in eyes with center-involved diabetic macular edema (CI-DME). Methods: Fifty-seven eyes of 36 patients with CI-DME were included in this prospective interventional case series. Structural optical coherence tomography (OCT) and enhanced depth imaging OCT were performed at baseline followed by three monthly 1.25 mg IVZ injections. Changes of SCT, CMT, and BCVA at each follow-up session were assessed. The association between baseline SCT and its monthly changes with final visual and anatomical outcomes were also assessed. Results: CMT at baseline, and at the first, second, and third month follow-up sessions were 396 ± 119, 344 ± 115, 305 ± 89, and 296 ± 101 μm, respectively (P-value < 0.001). SCT at baseline, and at months one, two, and three were 236 ± 47, 245 ± 56, 254 ± 54, and 241 ± 54 μm, respectively (Pvalue > 0.99). Corresponding figures for BCVA were 0.58 ± 0.29, 0.47 ± 0.31, 0.4 ± 0.24, and 0.37 ± 0.23 LogMAR, respectively (P-value < 0.001). There was a statistically significant positive correlation between BCVA and CMT changes following IVZ injections (P-value < 0.001). However, there were no significant correlations between SCT changes and visual acuity (VA) and CMT changes following IVZ injections. Conclusion: IVZ improved visual outcomes and macular thickness profiles in patients with CI-DME. However, IVZ had no significant effect on SCT. Baseline SCT and its monthly changes had no association with visual and anatomical outcomes

Childhood Pars Planitis; Clinical Features and Outcomes

Purpose: To evaluate the demographic and clinical features of childhood pars planitis, and to determine the therapeutic and visual outcomes of the disease. Methods: Medical records of pediatric patients (less than 16 years of age at diagnosis) with pars planitis and at least 6 months of follow-up who were referred to Labbafinejad Medical Center, Tehran, Iran over a 22 year period were reviewed. Results: Overall, 117 eyes of 61 patients including 51 (83.6%) male subjects were included. Mean age at the time of diagnosis was 7.8΁3.2 (range, 3-16) years. Mean best corrected visual acuity (BCVA) was 0.88΁0.76 logMAR at presentation which improved to 0.39΁0.51 logMAR at final visit (P<0.001). Endotheliitis was present in 23 (19.6%) eyes and was significantly more prevalent in subjects younger than 9 years (P=0.025). Cataract formation (41.9%) and cystoid macular edema (19.7%) were the most prevalent complications. Univariate regression analysis showed that better baseline visual acuity (OR=0.38, 95%CI 0.21-0.70, P=0.002), age older than 5 years at disease onset (OR=0.36, 95%CI 0.14-0.9, P=0.029), absence of endotheliitis (OR=0.39, 95%CI 0.15-0.99, P=0.047) and female gender (OR=3.77, 95%CI 1.03-13.93, P=0.046) were significantly associated with final BCVA of 20/40 or better. Conclusion: Childhood pars planitis was much more common among male subjects. Endotheliitis may be a sign of inflammation spillover and is more prevalent in younger patients. Visual prognosis is favorable in most patients with appropriate treatment