Finite Element Calculation of the Polymer Stamp Material Redistribution under Restrictions on Fatigue Life

The numerical method of stamp topological optimization taking into account fatigue strength is presented in the work. It is proposed to take into account the restrictions on the stress state in accordance with the curve of the dependence of the maximum stresses on the number of loading cycles in the ESO topological optimization method. An approach to the selection of the evolutionary coefficient with a step-by-step increase in the rejection coefficient is proposed when constructing an iterative scheme for the rejection of elements by the method of topological optimization. The calculation of the stamp optimal topology with a decrease in volume due to the removal and redistribution of material was carried out in the study. The new geometric model of the optimal topology stamp is based on the predicted distribution of elements with a minimum stress level. The verification calculation of the stress state of the stamp of optimal topology with an assessment of fatigue strength was carried out in the work. The numerical calculation was carried out using the finite element method in the Ansys software package. The minimized stamp volume decreased by 35% according to the calculation results. The results of the study can be further applied in the development of topological optimization methods and in the design of stamping tools of optimal topology.

Intrinsic Dependence of Groundwater Cation Hydraulic and Concentration Features on Negatively Charged Thin Composite Nanofiltration Membrane Rejection and Permeation Behavior

Commercial nanofiltration membranes of different molecular weight cut-offs were tested on a pilot plant for the exploration of permeation nature of Ca, Mg, Mn, Fe, Na and ammonium ions. Correlation of transmembrane pressure and rejection quotient versus volumetric flux efficiency on nanofiltration membrane rejection and permeability behavior toward hydrated divalent and monovalent ions separation from the natural groundwater was observed. Membrane ion rejection affinity (MIRA) dimension was established as normalized TMP with regard to permeate solute moiety representing pressure value necessary for solute rejection change of 1%. Ion rejection coefficient (IRC) was introduced to evaluate the membrane rejection capability, and to indicate the prevailed nanofiltration partitioning mechanism near the membrane surface. Positive values of the IRC indicated satisfactory rejection efficiency of the membrane process and its negative values ensigned very low rejection affinity and high permeability of the membranes for the individual solutes. The TMP quotient and the efficiency of rejection for individual cations showed upward and downward trends along with flux utilization increase. Nanofiltration process was observed as an equilibrium. The higher the Gibbs free energy was, cation rejection was more exothermic and valuably enlarged. Low Gibbs free energy values circumferentially closer to endothermic zone indicated expressed ions permeation.

SIMULATION OF AN ELECTROMYOGRAPHIC SIGNAL CONVERTER FOR ADAPTIVE ELECTRICAL STIMULATION TASKS

The subject matter of the article is an electromyographic signal transducer, which are an integral part of devices for adaptive electrical stimulation of muscle structures based on reverse electromyographic communication. The goal of the work is to study the features, obtaining the corresponding theoretical relationships and computer modeling of a differential biopotential converter, providing amplification of the useful component and suppression of harmful interference, the spectra of which intersect. The following tasks were solved in the article: determining the effect of electrode width and electrode spacing on crosstalk; formation of the electrode-skin model and the input circuit of the transducer, obtaining theoretical relations for calculating the rejection coefficient, construction of the transducer circuit and its computer simulation. The following methods were used – methods of mathematical modeling of processes and technical devices; methods of analysis, structural and parametric synthesis of nonlinear electronic circuits; methods of machine design. The following results were obtained – a biopotential amplifier circuit with tracking feedback on power supply is proposed; modeling of dynamic processes by means of the Multisim program was carried out; on the basis of the constructed model of the electrode-skin input circuit and the obtained analytical relationships, the rejection coefficient of the input circuit of the equivalent circuit is calculated; the requirements for the signal registration module are formulated. Conclusions: The considered version of the electromyographic signal converter circuit based on tracking communication on power supply, effectively rejects 50 Hz common mode noise. On the basis of the constructed equivalent model of the input circuit of the amplifier, the theoretical relation for calculating the rejection coefficient of such amplifiers. The circuit is simulated in the Multisim program, the results confirmed the correctness of its functioning. The requirements for the interelectrode distance and the thickness of the electrodes themselves are also formulated. The results obtained can be used to design complexes for adaptive electrical stimulation.

Oily Water Separation Process Using Hydrocyclone of Porous Membrane Wall: A Numerical Investigation

This research aims to study the process of separating water contaminated with oil using a hydrocyclone with a porous wall (membrane), containing two tangential inlets and two concentric outlets (concentrate and permeate), at the base of the equipment. For the study, the computational fluid dynamics technique was used in a Eulerian–Eulerian approach to solve the mass and linear momentum conservation equations and the turbulence model. The effects of the concentration polarization layer thickness and membrane rejection coefficient on the permeate flow, hydrodynamic behavior of the fluids inside the hydrocyclone, and equipment performance were evaluated. Results of the velocity, transmembrane pressure and oil concentration profiles along the equipment, and hydrocyclone performance are presented and analyzed. The results confirmed the effect of the membrane rejection coefficient on the equipment performance and the high potential of the hydrocyclone with a porous wall to be used in the oil–water mixture separation.

Territorial inequality: an agent-based approach in modelling of social policy

The article proposes a methodological approach for assessing the territorial inequality based on an agent-oriented spatial model. The main decisions are made in the model at the microeconomic level by households and enterprises with spatial coordinates. Then they are aggregated to the level of regions, industries and the economy as a whole. The evaluation of the indicators according to the criterion of social justice is carried out using two groups of methods: firstly, statistical, primarily the Gini coefficients (which are based on the households’ incomes in regions or country as a whole), and secondly, methods for constructing isoelastic social welfare functions at the national and regional or zonal levels, which are based on the households’ utility functions and include the inequality rejection coefficient. Each value of the coefficient corresponds to a certain concept of social justice. This second group of methods is related to the original approach of the author. The model simulates the development of the government social policy, which is carried out by changing taxes and transfers and taking into account the degree of territorial inequality. Model calculations consider pensions and five types of monetary transfers in a fixed structure: unemployment benefits, child benefits, poverty benefits, social aid and basic income benefits. In a series of experiments, the effect on territorial inequality of changes in the total value of social transfers (with their fixed structure) and tax rates in accordance with the proportionality coefficients was assessed. It is used as a toolkit for changing the system of taxes and transfers and for supporting social policy to reduce spatial inequalities in Russia.

Removal of Different Dye Solutions: A Comparison Study Using a Polyamide NF Membrane

The removal of organic dyes in aquatic media is, nowadays, a very pressing environmental problem. These dyes usually come from industries, such as textiles, food, and pharmaceuticals, among others, and their harm is produced by preventing the penetration of solar radiation in the aquatic medium, which leads to a great reduction in the process of photosynthesis, therefore damaging the aquatic ecosystems. The feasibility of implementing a process of nanofiltration in the purification treatment of an aqueous stream with small size dyes has been studied. Six dyes were chosen: Acid Brown-83, Allura Red, Basic Fuchsin, Crystal Violet, Methyl Orange and Sunset Yellow, with similar molecular volume (from 250 to 380 Å). The nanofiltration membrane NF99 was selected. Five of these molecules with different sizes, shapes and charges were employed in order to study the behavior of the membrane for two system characteristic parameters: permeate flux and rejection coefficient. Furthermore, a microscopy study and a behavior analysis of the membrane were carried out after using the largest molecule. Finally, the Spiegler–Kedem–Katchalsky model was applied to simulate the behavior of the membrane on the elimination of this group of dyes.

Tailoring and Remotely Switching Performance of Ultrafiltration Membranes by Magnetically Responsive Polymer Chains

Magnetically responsive ultrafiltration membranes were prepared by grafting poly(2-hydroxyethyl methacrylate) chains from the outer surface of 100-kDa regenerated cellulose ultrafiltration membranes. Surface-initiated atom transfer radical polymerization was used to graft the polymer chains. Grafting from the internal pore surface was suppressed by using glycerol as a pore-filling solvent during initiator immobilization at varied densities. Glycerol suppresses the initiator attachment to the pore surface. Polymerization times of up to four hours were investigated. Superparamagnetic nanoparticles were covalently attached to the chain end. Membrane performance was determined using bovine serum albumin and dextran as model solutes. Increasing the grafted polymer chain density and length led to a decrease in the permeate flux and an increase in the apparent rejection coefficient. In an oscillating magnetic field, movement of the grafted polymer chains led to a decrease in the permeate flux, as well as an increase in the apparent rejection coefficient of the model solutes.

Hollow Fiber Ultrafiltration Membrane for Methyl Green Dye Removal

In this study, the behavior of a Polyvinyl chloride (18 wt % PVC) hollowfiber ultrafiltration (UF) membrane for methyl green (MG) dye removalfrom aqueous solution was estimated by studying the influence of varyingthe operation conditions (the concentration of the dye and volumetric flowrate) to determine their impact on the separation processes (permeate fluxand rejection coefficient) at constant pressure and temperature. The PVCmembrane was characterized by scanning electron microscopy.Furthermore, tests of the UF were carried out with pure water and MGaqueous solutions as feed. Outcomes explained a notable influence of feedconcentration and flow rate on the rejection and permeate flux, with thehighest rejection coefficient value close to 75.2% of the membrane system,at neutral pH.

The Improvement of Hydrophilic Property of Polyethersulfone Membrane with Chitosan as Additive

Membrane technology has been implemented broadly for clean water treatment. To produce a better membrane, modification is carried out by adding chitosan into a polymer solution. Materials used in this research are polyethersulfone (PES) 18%, the n-methyl pyrrolidone solvent modified with a chitosan solution (at 0.2 – 1 wt%) as an additive, and deionized water as a non-solvent. The membrane synthesis is carried out with the non-solvent induced phase separation method of blending the polymer. Membrane characterization includes functional group analysis, morphological structure, and water contact angle. Membrane performance is monitored at the filtration process, resulting in the permeability coefficient, and for the rejection of a contaminant (humic acid) with dead-end filtration. Research results show that the modified membrane characterization has an asymmetric morphological structure with a thinner top layer, and the membrane sublayer has a finger-like macrovoid structure with a larger size as compared to the original PES membrane (without the chitosan solution addition). The chitosan additive into the PES membrane improves the membrane’s hydrophilic property. The highest value of the permeability coefficient is achieved with a 1% chitosan addition, which provides a permeability coefficient value of 10.524 L/m2.h.bar and a rejection coefficient of 70.3%.

Optimization of Enhanced Ultrafiltration Conditions for Cd with Mixed Biosurfactants Using the Box-Behnken Response Surface Methodology

A mixture of the environmentally friendly biosurfactants rhamnolipids and sophorolipids was used as a source of micelles in this study. The Box-Behnken design and response surface methodology was used to investigate the influence of factors on micellar-enhanced ultrafiltration (MEUF). Simulated Cd-containing wastewater was used for testing. Based on single-factor experiments, the initial Cd2+ concentration, biosurfactant mixing ratio (α) and pH were chosen as influential variables, and both the Cd2+ rejection coefficient and permeation flux were used as responses. A predictive model based on a quadratic polynomial regression equation was established to determine the optimized enhanced ultrafiltration conditions for Cd. The results show that the regression equation is extremely significant and fits the data accurately. The optimal enhanced ultrafiltration conditions are as follows: initial Cd2+ concentration of 10.0 mg/L, α of 0.30 and pH of 9.58. Under these conditions, the rejection coefficient and the permeation flux of Cd2+ are 99.14% and 37.36 L/m2·h, respectively. The experimental results confirm that the experimental values agree well with the values predicted by the model. Further, these results provide theoretical support for using MEUF to treat heavy metal-containing wastewater when biosurfactants are used for micelle formation.