All Articles

Summary: Two new classes of gemini cationic surfactants— hexanediyl-1,6-bis[(isopropylol) alkylammonium] dibromide {in the abbreviation form: CnC6Cn[iPr-OH] and CnC6Cn[iPr- OH]2; alkyl: CnH2n + 1 with n = 9, 10, 12 and 14}—have been synthesized by interaction of alkyl bromides with N,N0-di- (isopropylol)-1,6-diaminohexane and N,N,N0,N0-tetra-(isopropylol)- 1,6-diaminohexane. The surface tension, electrical conductivity, and dynamic light scattering (DLS) techniques were used to investigate the aggregation properties of the gemini cationic surfactants in aqueous solution. The formation of critical aggregates at two concentrations in an aqueous solution from obtained gemini cationic surfactants were determined via the tensiometric method. Thus, these gemini cationic surfactants start to form aggregates at concentrations well below their critical micelle concentrations (CMC). The surface properties and the binding degree (β) of the opposite ion were tested against the length of the surfactant hydrocarbon chain and the number of the isopropylol groups in the head group. By applying the DLS technique, it was explored that how the number of isopropylol groups in gemini cationic surfactants with C12H25 chain affects the sizes of micelles at concentrations greater than CMC. It was discovered that the obtained gemini cationic surfactants have a biocidal character.

Summary: Different head-group containing ionic-liquid cationic surfactants (ILCS) are synthesized by the reaction of 1-bromododecane and various alkylethanolamines ([mono(2-hydroxyethyl)amine, methyldiethanolamine, di(2- hydroxyethyl)amine, tris(2-hydroxyethyl)amine, 2-(methylamino)ethanol, N-2-(dimethylamino)ethanol, 2- (dimethylamino)ethanol]), which hold 2-hydroxyethyl group functionality. By tensiometric and conductometric measurements, surface parameters of the synthesized ILCSs are investigated. Variation of the colloid-chemical parameters with a change in the head group (e.g., replacing methyl-with ethyl- and 2-hydroxyethyl fragments) is recorded. The synthesized ILCSs antimicrobial properties are studied. Microbial assay analysis shows that C12DEA is the most effective biocide relative to other ILCS. New polyelectrolyte-surfactant complexes are also synthesized via stepwise procedure: Acrylic acid and potassium acrylate are polymerized and obtained polymer is propoxylated, then exploiting di(2-hydroxyethyl)amine and tris(2-hydroxyethyl)amine, the synthesized propoxylated acrylic polymers are neutralized. Our studies reveal that the synthesized polyacrylate surfactant complexes are promising substances for oil recovery.

Summary: Ionic liquid (IL) surfactants were prepared from 1-bromododecane and ethanolamines (2-dimethyl- and 2-diethylethanolamines) in an equimolar ratio to reveal how their oil-collecting and dispersing ability is infl uenced by the structure of the alkyl fragment. The surface activity of the substances synthesized was studied tensiometrically, and the electrical conductivity, conductometrically. The eff ect exerted on the colloid-chemical parameters of the surfactants by the replacement of the methyl fragment in the head group by the ethyl fragment is described. The relative oil-collecting and oil-dispersing ability of these substances was evaluated under laboratory conditions by the example of a thin oil fi lm on the surface of waters with diff erent levels of mineralization.

Summary: The reaction of 1,4-bis(2-hydroxypropyl)piperazine with alkyl bromides produced cationic gemini surfactants at a 1:2 molar ratio. Tensiometric, conductometric, and dynamic light scattering techniques were employed to measure the surface activity, specific electrical conductivity, and aggregate size of the obtained gemini surfactants, respectively. The critical micelle concentration, polar group cross-sectional area, maximum adsorption, surface pressure, degree of counterion association, and Gibbs free energy variations during micelle formation and adsorption processes were computed based on the obtained data. It was established how the length of the hydrophobic group in gemini surfactants affected their colloidchemical characteristics. The antibacterial properties of these compounds were evaluated using the disk-diffusion method against various Gram-positive and Gram-negative bacteria, as well as fungi. Researchers also investigated the C12 chain gemini surfactant's capacity to prevent corrosion of mild steel in a CO2-saturated NaCl solution.

Summary: The article considers the effect of the properties of wood chip materials on the sharpening of circular saw blades with the aim to develop new technologies of sharpening cutting tools. The characteristic wear of saw blade teeth is investigated, and features of teeth sharpening are considered. The influence of imbalance on wear and sharpening of circular saw blades is analyzed.

Summary: This study proposes a new queue-dependent (s, S)-type replenishment policy in the queueing-inventory systems. If the inventory level is greater than s, no restocking order is sent; otherwise, the replenishment is performed to reach the maximum value S, regardless of the stock level at the moment. Orders are replenished in two ways: the regular order and the urgent order. Lead times of the two-type orders are exponentially distributed with different parameters. The urgent orders require a shorter delivery time than the regular orders. The queue-dependent replenishment policy is defined as follows: when the inventory level drops to s, if the number of the customers is less than predefined threshold value r, the regular order is made; if the number is more or equal r, the urgent order is sent. When the inventory level drops to zero, one customer becomes impatient, regardless of the customer’s number in the queue. Arrival of customers is according to a Markovian arrival process and the service times are adapted by a phase-type distribution. The mathematical model of the system is developed using a continuous-time Markov chain with an infinite state space. Stability condition and then the steady-state distribution are derived by using the matrix-geometric method. The influences of the parameters on the performance measures are discussed with numerical examples. An optimization problem is solved, where the criterion is the expected total cost, and the controlled parameters are the reorder point s and the threshold parameter r.

Summary: The study investigates the nexus between innovation, labor migrations, energy consumption and CO2 emissions in Germany for the period 1990–2020. This study applied a dynamic simulated ARDL (DS-ARDL) model for estimation, which can observe the negative and positive variations in variables both in long run and short run. The dependent variable in DS-ARD provides a more intuitive picture of dynamic effects than coefficients alone. In Addition, DS-ARDL may provide reliable estimations even if sample size is smaller. The results of this study suggest a long-term relationship among innovation, migration, energy consumption, and CO2 emissions. The results also confirm that migration has a positive relationship with CO2 emissions, while innovation has an adverse effect on CO2 emissions in long run. Policymakers can take action on both ends of the supply and demand spectrum to lessen the impact of migration on Germany's CO2 emissions. Human capital accumulation provided by international migration; therefore, receiving countries should encourage rapid technological advancement and improve their citizens' spending habits.

Summary: In this paper we consider the Dirichlet problem for the Laplace equation in Hardy classes generated by an additive-invariant Banach function space on the unit circle. It is shown that the classical Dirichlet problem for the Laplace equation has a unique solution for every boundary function from the considered space. It is considered a boundary problem for the Laplace equation with oblique derivatives in the Hardy classes generated by separable subspaces of rearrangement-invariant spaces in which the infinitely differentiable functions are dense. Noetherness of this problem is established and the index of this problem is calculated.

Summary: We determine the set of algebraic points of degree degree l ≥ 2 over Q on the curve X given by the affine equation n2 = 3(m5 −1) and this result extends a result of Siksek who described in [5] the set of algebraic points of degree 1 on this curve.

Summary: Let G be a locally compact hypergroup and let K be a compact subhypergroup such that (G,K) is a Gelfand pair. Let μ be a bounded complex-valued Borel measure on G , and let T♮μ be the corresponding convolution operator of L1♮(G), the subset of L1(G) consisting of K-bi-invariant functions. Suppose that S is a bounded linear operator on a Banach space X. We prove that every linear operator Ψ : X −→ L1♮(G) such that ΨS = T♮ μΨ is continuous if and only if (S, T ♮ μ) has no critical eigenvalues.