Methacrylate-functionalized POSS influence on cross-linking and mechanical properties of styrene-butadiene rubber

Iranian Polymer Journal - The addition of methacrylate-functional polyhedral oligomeric silsesquioxane (MA-POSS) nanoparticles to styrene-butadiene rubber (SBR) composites was evaluated in terms of...     

Polyhedral oligomeric silsesquioxane-based hybrid networks obtained via thiol-epoxy click chemistry

A series of hybrid networks based on polyhedral oligomeric silsesquioxane (POSS) were prepared by thiol-epoxy click reaction using commercially available octakis-glycidyl-POSS (G-POSS), trimethylolpropane triglycidyl ether, and trimethylolpropane tris(3-mercaptopropionate) as monomers. The click reaction was simply catalyzed by lithium hydroxide which proceeded readily at ambient conditions in very good yields. The incorporation of G-POSS into the network was clearly determined by transmission electron microscopy, FTIR, and ¹H-NMR spectroscopy techniques performed with a model study using 1-butane thiol and G-POSS molecules. The homogeneous distribution of G-POSS up to 5 wt% in the hybrid network was apparently confirmed by morphological investigations. By increasing G-POSS content higher than 5 wt%, the heterogeneous dispersion of G-POSS was determined from the tensile strength measurements. The significant decrease in tensile strength was possible due to the agglomeration of G-POSS. On the other hand, thermal properties of hybrid networks were compared together by thermogravimetric analyses, where all samples exhibited one-step degradation in the range of 220–500 °C. The thermal decomposition of hybrid network led to complete degradation of the organic part and favored the formation of stable carbonaceous and inorganic residues as char. Thus, the char yields of hybrid networks were increased to 6.2, 7.8, 10.1, 12.7, and 15.1% by G-POSS loadings from 0 to 15 wt%. This improvement was also a proof of the incorporation of G-POSS into the hybrid networks that resulted in high heat-resistant POSS-based hybrid networks compared to a sample without G-POSS.     

Multiphonon Intracenter Relaxation of Boron Acceptor States in Diamond

Semiconductors - The relaxation rates are calculated in the adiabatic approximation, in which the steady-state impurity states are taken to be electronic-vibrational (vibronic) states. The...     

Features of establishing regimes of limited speed in power-regulation systems

Features of setting up regimes of limited speed in power-regulation systems in which there is no feedback regarding speed and position are considered. It is suggested to introduce feedback regarding speed and position when the coordinates of an electric motor exceed maximum allowable values. Results of mathematical modeling and an example of practical implementation of the proposed control system are stated.     

A cascade laser on shallow-donor transitions in δ-Doped GaAs/AlGaAs superlattices

The possibility of amplification of terahertz-range electromagnetic waves due to optical transitions between a two-dimensional continuum and shallow-level donor states in GaAs/AlGaAs superlattices with selectively δ-doped quantum wells is analyzed theoretically. The population inversion required for the gain is attained under the conditions of vertical transport in the superlattice due to the hybridization of states in neighboring quantum wells coupled via electron tunneling through the barrier. It is shown that, at a doping level of 5 × 10¹⁰ cm^?2 per period, the gain can be as high as 50 cm^?1 at wavelengths 100–120 μm. The current density under operating conditions is ～50 A/cm².     

On the radiative recombination and tunneling of charge carriers in SiGe/Si heterostructures with double quantum wells

For SiGe/Si(001) epitaxial structures with two nonequivalent SiGe quantum wells separated by a thin Si barrier, the spectral and time characteristics of interband photoluminescence corresponding to the radiative recombination of excitons in quantum wells are studied. For a series of structures with two SiGe quantum wells different in width, the characteristic time of tunneling of charge carriers (holes) from the narrow quantum well, distinguished by a higher exciton recombination energy, to the wide quantum well is determined as a function of the Si barrier thickness. It is shown that the time of tunneling of holes between the Si_0.85Ge_0.15 layers with thicknesses of 3 and 9 nm steadily decreases from ~500 to <5 ns, as the Si barrier thickness is reduced from 16 to 8 nm. At intermediate Si barrier thicknesses, an increase in the photoluminescence signal from the wide quantum well is observed, with a characteristic time of the same order of magnitude as the luminescence decay time of the narrow quantum well. This supports the observation of the effect of the tunneling of holes from the narrow to the wide quantum well. A strong dependence of the tunneling time of holes on the Ge content in the SiGe layers at the same thickness of the Si barrier between quantum wells is observed, which is attributed to an increase in the effective Si barrier height.     

On the Two-Phonon Relaxation of Excited States of Boron Acceptors in Diamond

Semiconductors - The relaxation of holes from excited states of boron acceptors in diamond with the emission of two optical phonons is studied theoretically. To describe the wave function of...     

Analysis of the flow of an irregular viscous fluid between two revolving cylinders

We propose a mathematical model for the flow of an irregular viscous fluid between two revolving cylinders in a bipolar coordinate system. We present an analytic solution of the system of equations obtained, and we also obtain formulas for determining velocity fields, temperature fields, and energy characteristics.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 2, pp. 256–262, February, 1976.