Dispersion of the local parameters of quasilocalized low-frequency vibrational modes in a low-temperature glass: direct observation via single-molecule spectroscopy

Spectra of single tetra-tert-butylterrylene chromophore molecules embedded in an amorphous polyisobutylene matrix as microprobes were recorded. The individual temperature dependences of the spectral linewidths for the same single molecules (SMs) in a broad temperature interval (1.6 < T < 40 K) have been measured. This enabled us to separate the contributions of tunneling two-level systems and quasilocalized low-frequency vibrational modes (LFMs) to the observed linewidths. The analysis of the T dependences yields the values of LFM frequencies and SM-LFM coupling constants for the LFMs in the local environment of a given chromophore. Pronounced distributions of the observed parameters of LFMs were found. This result can be regarded as the first direct experimental proof of the localized nature of LFMs in glasses.     

Asymmetric synthesis of polymer-supported cyanohydrin acetates

A bimetallic titanium(salen) complex has been used to catalyze the asymmetric addition of potassium cyanide to aldehydes attached to Wang resin giving polymer supported cyanohydrin propionates with up to 91% enantiomeric excesses.     

Chemical Bonding and Pressure‐Induced Change of the Electron Configuration of Ytterbium in β‐YbAgGa2

Single‐phase polycrystalline samples of the intermetallic compound β‐YbAgGa₂ were synthesized by inductive heating and subsequent annealing for eight weeks at 670 K. Magnetic properties were characterized by susceptibility measurements and indicated intermediate valence of ytterbium at ambient pressure. Angle‐dispersive X‐ray powder diffraction data of orthorhombic β‐YbAgGa₂ indicate stability of the phase in the investigated pressure range from 0.1 MPa (ambient pressure) to 19 GPa. The pressure‐induced volume decrease is accompanied by an increase of the effective valence from 2.17 at ambient conditions to 2.71 at 16 GPa as evaluated by X‐ray absorption spectroscopy at the Yb L_III threshold. Analysis of the chemical bonding in β‐YbAgGa₂ by integrating the electron density of the polyanion in basins as defined by the electron localization function results in an electron count Yb^2.7+[(Ag^0.2—)(Ga1(3b)^1.0—)(Ga2(4b)^1.5—)]. This finding is close to the expected values calculated by means of the Zintl rules and fits well the results of magnetic susceptibility measurements and XAS investigations.     

Optimal control synthesis for the constrained bilinear biquadratic regulator problem

Optimal process control with control constraints is a challenging task related to many real-life problems. In this paper, a single input continuous time constrained linear quadratic regulator problem, is defined and fully solved. The constraints include both bilinear inequality constraints and customary control force bounds. As a first step, the problem is reformulated as an equivalent constrained bilinear biquadratic optimal control problem. Next, Krotov’s method is used to solve it. To this end, a sequence of improving functions suitable to the problem’s new formulation is constructed and the corresponding successive algorithm is derived. The required computational steps are arranged as an algorithm and proof outlines for the convergence and optimality of the solution are given. The efficiency of the suggested method is demonstrated by numerical example.     

Towards stabilization of the potential response of Mn(III) tetraphenylporphyrin-based solid-state electrodes with selectivity for salicylate ions

Journal of Solid State Electrochemistry - We report a new type of solid-state electrode (type I) of a simple design with polyvinyl chloride membranes based on Mn(III) tetraphenylporphyrin and with...     

Depositing nanoparticles inside millimeter-size hollow tubing

The inner and the outer walls of hollow tubing with an inner diameter of 0.4-0.9 cm and an outer diameter of 0.6-1.3 cm were coated with silver nanoparticles (NPs) by a one-step process using ultrasound irradiation. The structure and morphology of the nanoparticles (NPs) inside the hollow tubing and on the outer surface were characterized using methods such as XRD, TEM, HR-TEM, and HRSEM. The inner surface of the tubing was found to be coated with more silver than the outer surface. The coating was done on tubing made of rubber, PVC, Teflon and polyethylene. Sonochemistry is demonstrated as a method for depositing nanoparticles on the inner wall of a tube.