Modified sol-gel method for synthesis of mesoporous silicon dioxide and study of the optical properties of antireflection coatings based on this material

The kinetics of sedimentation of aqueous kaolin dispersion in the presence of multicomponent fl occulating additives was studied. Binary and ternary mixtures based on poly-1,2-dimethyl-5-vinylpyridinium methyl sulfate, poly-N,N-dimethyl-N,N-diallylammonium chloride, and poly-N,N,N-trimethyl-Nmethacryloyloxyethylammonium methyl sulfate were used as flocculants. The synergistic effect of the cationic polyelectrolytes in such multicomponent systems was revealed.     

Output spectrum of Yb-doped fiber lasers

An analytical model for self phase modulation in Yb-doped fiber laser (YDFL) describing output spectrum and its broadening with increasing power has been developed. Spectral measurements in continuous wave (CW) cladding-pumped YDFL have proved the validity of the model demonstrating hyperbolic secant shape of the spectrum and linear increase of the line width with power in 1-12 W range. At lower powers, spatial hole burning and line self-sweeping effects become important and define the lower limit for the line width.     

Multiband wavelength demultiplexer based on digital planar holography for on-chip spectroscopy applications

A novel type of multiband wavelength demultiplexer for on-chip spectroscopy applications is proposed, and first results of the device fabrication and characterization are reported. The devices are based on computer-designed digital planar holograms, which involve millions of lines specifically located and oriented in order to direct output light into designed focal channels according to the wavelength. Devices operate in four individual bandwidths within the visible range (477.2-478.0 nm, 528.8-529.9 nm, 586.4-587.7 nm, 628.9-630.4 nm) with 96 channels and spectral channel spacing down to 0.0375 nm/channel.     

A novel ferrocenylalkylating reagent. Ferrocenylalkylation of imidazole and its derivatives

Reactions of α-(1-benzotriazolyl)ethylferrocene (1) with 1,2,4-triazole, imidazole, benzimidazole, and edenine have been studied in the MeOH−HCl, MeOH, and AcOH systems. Compound 1 is a novel ferrocenylalkylating reagent which, unlike α-hydroxyalkylferrocenes, is capable of alkylating imidazole, benzimidazole (even in the absence of an acid catalyst), and adenine (regioselectively at the N(3) position). The antitumor activity discovered for ferrocenylalkylazoles of the type 1 may be attributed to the ability of such compounds to ferrocenylalkylate nucleic bases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 172–174, January, 1997.     

Explicit mass renormalization and consistent derivation of radiative response of classical electron

The radiative response of the classical electron is commonly described by the Lorentz–Abraham–Dirac (LAD) equation. Dirac’s derivation of this equation is based on energy and momentum conservation laws and on regularization of the field singularities and infinite energies of the point charge by subtraction of certain quantities: “We... shall try to get over difficulties associated with the infinite energy of the process by a process of direct omission or subtraction of unwanted terms”. To substantiate Dirac’s approach and clarify the mass renormalization, we introduce the point charge as a limit of extended charges contracting to a point; the fulfillment of conservation laws follows from the relativistic covariant Lagrangian formulation of the problem. We derive the relativistic point charge dynamics described by the LAD equation from the extended charge dynamics in a localization limit by a method which can be viewed as a refinement of Dirac’s approach in the spirit of Ehrenfest theorem. The model exhibits the mass renormalization as the cancellation of Coulomb energy with the Poincaré cohesive energy. The value of the renormalized mass is not postulated as an arbitrary constant, but is explicitly calculated. The analysis demonstrates that the local energy–momentum conservation laws yield dynamics of a point charge which involves three constants: mass, charge and radiative response coefficient θ$\theta$. The value of θ$\theta$ depends on the composition of the adjacent potential which generates Poincaré forces. The classical value of the radiative response coefficient is singled out by the global requirement that the adjacent potential does not affect the radiated energy balance and affects only the local energy balance involved in the renormalization.     

Hollow cathode discharge (HCD) dark space diagnostics with laser photoionization and galvanic detection

We report on a new technique for measuring the cathode dark space width and the variation of ground state atomic density within it by measuring the ionization current generated by laser photoionization of neutral ground state metallic atoms. The technique is supported by a theoretical model of charge displacement in the dark space based on the assumption of a Lorentzian gas and thus on Langevin equations. After verifying the applicability of the theoretical approach, measurements of dark space width with respect to pressure, current and nature of the buffer gas are presented for an uranium HCD. Results of variation in density of ground state neutral uranium, in the dark space, versus current and pressure in Xe are also given. These last results are of interest when using photoionization currents in the HCD dark space for laser spectroscopy, such as photoionization studies of elements like uranium.     

Liquid scintillator based on linear alkylbenzene

The results of studies on optimizing the composition of a new liquid scintillator based on linear alkylbenzene are presented. Light yield, transparency, absorption and luminescence spectra are measured. For liquid scintillator samples placed in a 50 × 50 mm Teflon cylindrical cell, the energy resolution measured for 1 MeV electrons (²⁰⁷Bi) was 8%.     

Reactions of ferricinium salts with Lewis bases

A reaction of the ferricinium radical cation with Lewis bases leads to substitution in the cyclopentadienyl ring with the formation of ferrocene derivatives only when the radicals are formed from the Lewis bases in the process of the reaction.