Robust decomposed system control for an electro-mechanical linear actuator mechanism under input constraints

This paper aims to develop a robust decomposed system control (RDSC) strategy under input constraints for an electro-mechanical linear actuator (EMLA) facing model uncertainty and external disturbances. At first, a state-space model of a complex multi-stage gearbox EMLA system, driven by a permanent magnet synchronous motor (PMSM), is developed, and the non-ideal characteristics of the ball screw are presented through the model. The result is a four-order nonlinear strict-feedback form (NSFF) system decomposed into three subsystems. As the paper's main result, a novel RDSC strategy with uniform exponential stability for controlling subsystem states is presented. This developed controller avoids the "explosion of complexity" problem associated with backstepping by treating the time derivative of the virtual control input as an uncertain system term. The proposed method, despite assuming load disturbances and input constraints with arbitrary bounds, offers a straightforward control approach for a broader range of applications. Further, the controller's performance is evaluated by simulating two distinct duty cycles, each representing different levels of demand on the actuator facing load disturbances near the rated motor performance.     

Green bio-synthesis of Ni/montmorillonite nanocomposite using extract of Allium jesdianum as the nano-catalyst for electrocatalytic oxidation of methanol

In this work, synthesis of Ni nanoparticles was carried out successfully by water extract of Allium jesdianum as a biochemical reducing agent in the presence of montmorillonite clay (MMT) as a natural solid support for the first time. Then the electrochemical activity of the synthesized nanocomposite was investigated in methanol electrocatalytic oxidation. MMT with high cation exchange capacity and nano layer structure was exposed to ion exchange conditions in nickel solution. Then Ni²⁺ ion exchanged form was used in this process as a source of ions and also capping agent. Water extract of Allium jesdianum used as a reducing agent due to abundant availability of phenolic and flavonoid contents. The synthesized Ni/MMT nanocomposite was characterized using UV–Vis spectroscopy (UV–Vis), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDX). The surface of prepared modified electrode has been characterized using SEM to evaluate the morphology, showing uniform dispersion of Ni nanoparticles with mean diameter of 12 to 20 nm. The modified carbon paste electrode was then used in methanol electrocatalytic oxidation reaction. Methanol oxidation on the proposed modified electrode surface occurs at 0.6 V and 0.3 V in alkaline and acidic medium respectively. Also, the results showed the better performance of modified electrode toward methanol electrocatalytic oxidation in comparison with carbon paste electrode that is modified by ion exchanged MMT. Charge transfer coefficients and apparent charge transfer rate constant for the modified electrode in the absence of methanol in alkaline medium were respectively found as: α_a = 0.53, α_c = 0.37 and k_s = 1.6 × 10⁻¹ s⁻¹. Also, the average value of catalytic rate constant for the electrocatalytic oxidation of methanol by the prepared nano-catalyst was estimated to be about 0.9 L·mol^-1·s^-1 by chronoamperometry technique. The prepared electrode was also effective for electrocatalytic oxidation of ethanol and formaldehyde in alkaline medium.     

Numerical investigation of the energy separation effect and flow mechanism inside convergent,straight, and divergent double‐sleeve RHVT

This study provides analysis of a cooled Ranque–Hilsch vortex tube (RHVT) with various specifications. It shows how cooling influences energy conversion inside the RHVT and improves performance of the device in separation of hot gas from the cold stream within the fluid by presenting the temperature detachment (the temperature diminution of cold air (ΔT_c = T_i ? T_c), isentropic efficiency (η_is), and coefficient of performance (COP) of divergent, convergent, and straight VTs. Two key parameters including hot tube length and number of nozzles for cooling and insulated cases are investigated to find out how the performance of the VT is affected by different geometry configurations under cooling conditions. These influences were researched for straight, convergent, and divergent VT separators under different flow characteristics. The optimum geometrical conditions for the cooling cases were identified. Results are indicative of positive influence of cooling for energy separation inside a VT. The quantities of ΔT_c, η_is, and COP for the cooled RHVT are greater than uncooled RHVT for various types of VTs. Cooling the VTs leads to an increase of 12.5% in ΔT_c, 14.4% in η_is, and 15.1% in COP when the base case was an uncooled VT.     

Removal of methylene blue dye from aqueous solutions by a new chitosan/zeolite composite from shrimp waste: Kinetic and equilibrium study

The adsorption of methylene blue dye (MBD) from aqueous solutions was investigated using a new composite made up of shrimp waste chitosan and zeolite as adsorbent. Response surface methodology (RSM) was used to optimize the effects of process variables, such as contact time, pH, adsorbent dose and initial MBD concentration on dye removal. The results showed that optimum conditions for removal of MBD were adsorbent dose of 2.5 g/L and pH of 9.0, and initial MBD concentration of 43.75 mg/L and contact time of 138.65 min. The initial concentration of dye had the greatest influence on MBD adsorption among other variables. The experimental data were well fitted by the pseudo-second order kinetic model, while the Freundlich isotherm model indicated a good ability for describing equilibrium data. According to this isotherm model, maximum adsorption capacity of the composite was 24.5 mg/g. Desorption studies showed that the desorption process is favored at low pH under acidic conditions.     

Application of scientometric methods to chemical research in Iran: Reflections on Iran&;#39;s current science policy

Summary Following a brief historical account of the initial difficulties of introducing modern sciences, especially the Western art of independent scientific inquiry, into Iran, using data obtained from the ISI (http://access.isiproducts.com/trials) an attempt is made to analyze the apparent present successes of Iranian scientists on the international science market. Using the corresponding ISI data of the publications (1990-2003) of 24 selected young chemistry Ph.D. graduates and present faculty members at various internal academia, a quantitative and qualitative assessment (www.geocities.com/iipopescu) of their achievements has been attempted and the results related to the strengths and weaknesses of the present science policy of the country.     

Design of ultrahigh-speed low-voltage CMOS CML buffers and latches

A comprehensive study of ultrahigh-speed current-mode logic (CML) buffers along with the design of novel regenerative CML latches will be illustrated. First, a new design procedure to systematically design a chain of tapered CML buffers is proposed. Next, two new high-speed regenerative latch circuits capable of operating at ultrahigh-speed data rates will be introduced. Experimental results show a higher performance for the new latch architectures compared to the conventional CML latch circuit at ultrahigh-frequencies. It is also shown, both through the experiments and by using efficient analytical models, why CML buffers are better than CMOS inverters in high-speed low-voltage applications.     

Oxidation of Primary Amines to N‐Monoalkylhydroxylamines using Sodium Tungstate and Hydrogen Peroxide‐Urea Complex

The sodium tungstate‐catalyzed (10 mol %) oxidation of primary amines with a urea‐hydrogen peroxide complex (UHP) gives the corresponding N‐monoalkylhydroxylamines, which are important biologically active compounds, in good to excellent yields. The method is applicable for a wide range of primary amines, including chiral benzylic amines, α‐1,2‐hydroxylamine and α‐amino esters.     

Investigation of Bonding Behavior of AA1050/AA5083 Bimetallic Laminates by Roll Bonding Technique

In this study, 1-mm AA1050/AA5083 bimetallic laminates were produced using roll bonding (RB) process. The RB process was carried out with thickness reduction ratios of 25, 50 and 75%, separately. Finite element simulation was used to model the deformation of bimetallic laminates for various experimental conditions. Particular attention was focused on the bonding of the interface between AA1050 and AA5083 layers in the simulation. The optimization of thickness reduction ratios was obtained for improvement of the bond strength of bimetallic laminates during RB process. During the simulation, the mean equivalent strain at the interface zone between the layers was found to reach the maximum value with a high quality bond for the sample produced with 75% of thickness reduction. Moreover, the fracture surface of samples around the interface of laminates after the tensile test was studied to investigate the bonding quality by scanning electron microscopy.     

A wavelet approach for the variable-order fractional model of ultra-short pulsed laser therapy

In this paper, the ultra-short pulsed laser treatment is numerically simulated for a focused laser beam applied to a cylindrical domain. To do so, the general form of the variable-order fractional-order, dual-phase lag bioheat transfer equation is implemented. To determine the major affecting parameters, the dimensionless form of the heat equation is derived and solved numerically. An efficient method based on the 2D Legendre wavelets is developed to provide a numerical solution for this variable-order time fractional model. The man advantage of the proposed algorithm is that it converts the solution of the problem into solution of a system of algebraic equations. The validity of the formulated method is investigated through one numerical example. The effect of several operational and thermo-physical properties including the phase lag time, fractional order, and the duration of active laser beam in each on/off cycle on the thermal field and heat penetration depth is examined. According to the results, it is concluded that by increasing the fractional order from 0.1 to 0.9, 65.1% increase in the penetration length occurs.