Synthesis and characterization of poly(N-propionyl)iminoethylene

Summary The cationic polymerization of 2-ethyl-2-oxazoline using CH₃I as initiator at different monomer/initiator ratios, temperatures, solvents and times of polymerization was carried out. The effect of these variables on the polymerization yield and viscosity of the polymers was studied. The poly(N-propionyl)iminoethylene was hydrolyzed in acid medium obtaining a linear poly(ethyleneimine) (PEI). All the polymers were characterized by elemental analysis, IR,¹H NMR, and¹³C NMR spectroscopy.     

Reactivity of platinum nanoaggregates in catalytic reduction of U(VI) with hydrazine in acid solutions

Catalysts Pt/SiO₂ with different size of Pt nanoaggregates were studied in catalytic reduction of U(VI) with hydrazine in solutions of H₂SO₄, HClO₄, and HNO₃. The catalytic activity of the surface Pt atoms of Pt/SiO₂ in this reaction monotonically increases with an increase in the size of metal crystallites on the support, i.e., the negative size effect is observed. Catalytic reduction of U(VI) with hydrazine in H₂SO₄ solutions is significantly faster than in HClO₄ and HNO₃, and in HClO₄ it is slightly faster than in HNO₃. The results were interpreted within the framework of the concept of the energetic nonuniformity of the surface atoms and of the mechanisms of catalytic reduction of U(VI) with hydrazine in acid solutions.     

Distributions of multi-estimates for multistage stochastic inclusions

The problems of constructing recursive relations for conditional and unconditional distributions of random informational sets are considered. These sets, which are called multi-estimates in the paper, appear naturally in the problems of estimation of states and parameters of multistage stochastic inclusions.     

Selective control of the observables in the ensemble of quantum mechanical molecular systems

A new approach to synthesize algorithms for selective control of the observables in quantum mechanical systems in the presence of additional constraints during the whole period of control is proposed. Analytic results of achieving the goal of control under some additional assumptions were obtained. It was demonstrated that the error in achieving the goal of control is proportionate to the error in prescribing the initial state of system and the error in realizing the control action. Numerical results for the problem of selective control for energy of hydrogen molecules (H₂) with different isotopes are represented. The proposed algorithms are easy to design.     

Effects of Solvent Exchange Period and Heat Treatment on Physical and Chemical Properties of Rice Husk Derived Silica Aerogels

In this study, hydrophobic silica aerogels were synthesized from rice husk ash-derived sodium silicate through sol-gel processing, solvent exchange, surface modification and ambient pressure drying. By volume, 10% of trimethylchlorosilane (TMCS) in 90% of n-hexane was used as a hydrophobic solution in the surface modification process. The physical and chemical properties of silica aerogels were characterized by density and porosity measurements, scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller theory (BET) and dynamic scanning calorimetry (DSC). The hydrogels prepared were in the form of 2.5 ± 0.5 mm beads and then converted into alcogels through solvent exchange with ethanol for repetition of 3, 6 and 9 days. It is found that the optimal quality of silica aerogels with the BET surface area as high as 668.82 m²/g was obtained from the alcogels of the solvent exchange period of 9 days. Depending on the size of the gel’s block, a longer solvent exchange period will ensure adequate removal of pore water. Post heat treatment on silica aerogels obtained from the 9 days of solvent exchange at 200, 300 and 400 °C for 2 h results in slight decreased of aerogel’s density from 0.048 g/cm³ to 0.039 g/cm³ and the hydrophobicity of the aerogels is decreased above 380 °C as confirmed by DSC analysis.

     

Structure formation in production of yttrium-silicate materials by the sol-gel method

Materials made from yttrium silicates were synthesized by the sol-gel method. The effect of the amount of yttrium oxide, which varied from 10 to 50% (molar content), and the water:alcoholate molar ratio was investigated. Structure formation and the character of crystallization of gels in heat treatment in the 650–1300°C range were investigated. __________ Translated from Steklo i Keramika, No. 1, pp. 3–6, January, 2007.     

Aqueous and nonaqueous microemulsion systems with a palm oil-base emollient

Microemulsions with a palm oil-based emollient, i.e., medium-chain triglyceride (MCT), and water or glycerol, stabilized by two oppositely charged ionic surfactants and a medium-chain alcohol, were investigated. The results showed that only the water-in-MCT or the glycerol-in-MCT microemulsions were prominent. The maximum solubilization of the MCT emollient was higher in cetyltrimethyl ammonium bromide, i.e., the positively charged surfactant that contained a nitrogen atom, than the negatively charged surfactant sodium dodecyl sulfate. However, the results did not lend themselves for selecting any decisive factor that would explain the different solubilization behavior encountered in the investigated aqueous and nonaqueous systems.     

Electrochemical properties and solubility of URh<Subscript>3</Subscript> in nitric acid solutions

Electrochemical properties of the intermetallic compound URh₃ in 0.5–8 M HNO₃ solutions were studied by linear voltammetry. The electrochemical characteristics of URh₃ in nitric acid solution were determined for the first time using the Tafel equation. URh₃ is highly resistant to both chemical and anodic dissolution, which is due to formation of passive films on the electrode surface. All the anodic oxidation processes observed on the electrode led to secondary passivation of the alloy and not to its dissolution. The conclusions based on the electrochemical data were confirmed by experiments in 8 M HNO₃.     

Problem of reconstructing input signals under communication constraints

For a linear controllable system, the problem of reconstruction of all input signals, which are compatible with the measured signal, is considered. It is assumed that information can be transmitted in a processing center only via digital communication channel at discrete time instants, and the word length is limited. In this connection, there are encoding and decoding devices in the communication channel. For simplicity, the communication channel is assumed to be noiseless and delay-free. Defining relationships are obtained for the set of compatible input signals, as well as relationships between reconstruction precision, length of transmitted word and transmission frequency.