Stabilization of irregular systems

We consider the stabilization problem for the zero equilibrium of bilinear and affine systems in canonical form. We obtain necessary and sufficient conditions for the stabilizability of second-order bilinear and affine systems in canonical form and generalize these conditions to the case of simultaneous stabilization of a family of bilinear systems and to nth-order bilinear systems.     

Syntheses of four new pyridinium phenolates with caged phenolate functionalities as chromophores for quadratic optics

Semi-empirical calculations as well as our preliminary studies indicate an increase of the nonlinear response of pyridinium phenolates with the raise of their interplanar angle. Unfortunately, the tendency of previously synthesized zwitterionic compounds to form aggregates prevents their use in electro-optical devices. In order to understand the process of aggregation and to circumvent it, the syntheses of new pyridinium phenolates bearing alkyl chains of various length, caging the phenolate functionality, have been achieved and are described herein.     

The Contribution of Conceptual Change Texts Accompanied by Concept Mapping to Students' Understanding of the Human Circulatory System

The present study was conducted to investigate the contribution of conceptual change texts accompanied by concept mapping instruction to 10^th— grade students' understanding of the human circulatory system. To determine misconceptions concerning the human circulatory system, 10 eleventh-grade students were interviewed. In the light of the findings obtained from student interviews and related literature, the Human Circulatory System Concepts Test was developed. The data were obtained from 26 students in the experimental group taught with the conceptual change texts accompanied by concept mapping, and 23 students in the control group taught with the traditional instruction. Besides treatment, previous learning in biology and science process skills were other independent variables involved in this study. Multiple Regression Correlation analysis revealed that science process skill, the treatment, and previous learning in biology each made a statistically significant contribution to the variation in students' understanding of the human circulatory system. It was found that the conceptual change texts accompanied by concept mapping instruction produced a positive effect on students' understanding of concepts. The mean scores of experimental and control groups showed that students in the experimental group performed better with respect to the human circulatory system. Item analysis was carried out to determine and compare the proportion of correct responses and misconceptions of students in both groups. The average percent of correct responses of the experimental group was 59.8%, and that of the control group was 51.6% after treatment.     

Role of the n+1 amino acid residue on the deamidation of asparagine in pentapeptides

Deamidation plays an important role in biochemical phenomena such as aging. The role of the n + 1 residue on the deamidation of asparagine (asparagine being the nth residue) in three pentapeptide chains (GGNGG, GGNMG and GGNIG) has been analysed with hybrid computational tools. Potentials of mean force at 300 K were calculated from the MD/replica exchange simulations using weighted histogram analysis (WHAM) in explicit water. The snapshots were clustered taking into account the requirements of the plausible deamidation mechanisms, as such the tautomerisation of the asparagine side chain as initial step has been confirmed, based on the proximity of water to the deamidation site. The ultimate goal being to gain an insight on the peptide backbone N-H acidity, quantum mechanical calculations have been carried out. For this purpose, the distribution of Φ/Ψ, Φ₂/Ψ and end-to-end distances deduced from the WHAM diagrams have been considered and a total of 110 structures have been sampled. These neutral pentapeptides as well as their corresponding anions have been optimised (B3LYP/6-31++G(d,p)) in implicit water in order to gain an insight on the peptide backbone N-H acidity. In this study, we have shown that the open conformations of the neutrals and the anions, which display a β sheet like structure are well populated and their pK_as rank in the same order as the deamidating half-lives, that is the peptides that deaminate fastest can more readily access conformations that are more acidic.     

Bimodal size-distribution function in a nanoparticle ensemble formed during the laser irradiation of the surfaces of solids

A defect-deformational (DD) model of the formation of a nanoparticle ensemble on the surface of solids under multipulse laser ablation is developed. The DD theory of bimodal nanoparticle size distribution is developed, which expresses size distribution via the bimodal growth rate of DD surface gratings generated by laser irradiation. The obtained size-distribution function corresponds to the experimental data.     

Development of a new biosensor for superoxide radicals

A superoxide dismutase (SOD) biosensor for determination of superoxide radicals has been developed by immobilization of superoxide dismutase within gelatin (G) on a Pt electrode surface. The properties of the biosensor have been investigated and optimum conditions–enzyme concentration, glutaraldehyde concentration, and pH–were determined. The response of the G-SOD biosensor was proportional to concentration and the detection limit was 0.01 mmol L⁻¹ at a signal-to-noise ratio of 3. The biosensor retained 89% and 60% of its sensitivity after use for three and four weeks, respectively. Immobilization of SOD on gelatin provides a biocompatible microenvironment around the enzyme and stabilizes the activity of the enzyme very efficiently. The superoxide dismutase biosensor was used to determine the antioxidant properties of acetylsalicylic acid-based drugs and the anti-radical activity of healthy and cancerous human brain tissues.     

Acoustic emission and thermal expansion of Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> and Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> crystals

The temperature dependence of the elongation per unit length for Pb(Mg_1/3Nb_2/3)O₃ crystals unannealed after growth and mechanical treatment is investigated in the course of thermocycling. It is revealed that this dependence deviates from linear behavior at temperatures below 350°C. The observed deviation is characteristic of relaxors, is very small in the first cycle, increases with increasing number n of thermocycles, and reaches saturation at n≥3. In the first cycle, a narrow maximum of the acoustic emission activity is observed in the vicinity of 350°C. In the course of thermocycling, the intensity of this maximum decreases and becomes zero at n>3. For (1?x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ crystals, the dependence of the temperature of this acoustic emission maximum on x exhibits a minimum. It is assumed that the phenomena observed are associated with the phase strain hardening due to local phase transitions occurring in compositionally ordered and polar nanoregions.     

Bis(saccharinato)palladium(II) and platinum(II) complexes with 2,2′-bipyridine: Syntheses,structures, spectroscopic,fluorescent and thermal properties

New palladium(II) and platinum(II) complexes, cis-[Pd(bpy)(sac)₂] (1) and cis-[Pt(bpy)(sac)₂] (2), where sac = saccharinate, bpy = 2,2′-bipyridine, have been synthesized and characterized by elemental analysis, UV–Vis, IR, ¹H NMR and ¹³C NMR. The structures of the DMSO solvated complexes are determined by X-ray diffraction. Both complexes are isomorphous and the metal ions are coordinated by two N-bonded sac ligands, and two nitrogen atoms of pyridyl groups of bpy in a cis fashion. The mononuclear species interact each other through weak intermolecular C–H?O hydrogen bonds, C–H?π and π?π interactions leading to three-dimensional supramolecular networks. All complexes exhibit a high thermal stability in the solid state, and are fluorescent in the solution.     

Low-temperature oxidative modification of lignites and lignite-based cokes

The kinetics of oxidation of lignites and cokes with ozone in the gas and liquid phases and the composition of oxidation products were studied. The surface area and porosity were measured before and after ozonization. Ozonization increased the surface area largely because of the growth of micro-and mesopores. Changes in the composition of functional groups on the surface of lignites and cokes were determined IR spectroscopically. Adsorbents with the required properties can be prepared by varying the concentration of ozone and ozonization duration.     

Functional polymer nanocomposites containing triazole and carboxyl groups

New water-soluble functional polymer nanocomposites with nanoparticles of metallic silver in a matrix of 1-vinyl-1,2,4-triazole copolymers with crotonic acid have been synthesized. The resulting nanocomposites contain isolated silver nanoparticles 2–12 nm in diameter, preferably spherical in shape, and uniformly distributed in the polymer matrix. ATR IR spectroscopy has revealed that the nanoparticles affect the state of the carboxyl groups in the polymer matrix. It has been found that the size of zero-valent silver nanoparticles depends on the ratio of monomer units in the polymer matrix. The thermo-oxidative stabilities of the synthesized copolymers and polymer nanocomposites produced on their basis have been examined.