Influence of the UV radiation wavelength on the curing of oligourethaneacrylate compositions for protective coatings of optical fibers

The curing kinetics of films produced from compositions based on UV-curable oligourethaneacrylates is investigated using, as a source of radiation, an individual spectral line separated by a monochromator from the radiation of a DRT-400 mercury tubular lamp. It has been established that in the region of spectral sensitivity of the composition, the curing time of the film is inversely proportional to the intensity of volumetric absorption of the radiation-source photons by the initiator at the lower surface of the film under study. Individual contributions of some of the lines to the process of composition curing by using the integral spectrum of the radiation source have been evaluated. The spectral-kinetic results obtained were confirmed when using the compositions under study as protective coatings of optical quartz fibers.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 836–840, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

A stabilization law for two semi-infinite interacting strings of characters

We consider a Markov chain that describes the evolution of two interacting strings of symbols. The transitions probalitities of this Markov chain depend only on the rightmost symbols of both strings. The main goal of the present paper is to prove a limit theorem (stabilization law): the distribution of the rightmost symbols converges to some limit correlation function.1 Partially supported by FAPESP (2002/01501-9) and RFBR (02-01-00415)2 Partially supported by RFBR (02-01-00415)     

Use of the tagged neutron technique for detecting dangerous underwater substances

The tagged neutron technique (TNT) is analyzed in terms of its application for detecting dangerous substances hidden in underwater objects. The use of the technique for solving these problems is justified theoretically. The main characteristics of a prototype detector aimed at detecting explosives in a water environment are determined.     

Investigation into the significant effect of CuO additive on the synthesis of ZrSiO4: phase formation and crystallization at low temperature

Journal of Thermal Analysis and Calorimetry - The ZrSiO4 has been synthesized with CuO as mineralizer by sol–gel route at low temperature. The mineralization effect of the CuO on mechanism of...     

A Procedure for Measuring the Viscosity of Formulations Based on Oligourethane Acrylates for UV-Curable Protective Coatings of Fiber Light Guides

A capillary viscometric procedure was developed for measuring the viscosity of formulations based on oligourethane acrylates for UV-curable protective coatings of fiber light guides. The temperature dependences of the viscosities of these formulations were studied. The moduli of elasticity of fibers prepared from these formulations after UV curing were measured. These formulations can be stably applied, using a die, to the surface of fiber light guides in the course of their drawing at a drawing rate of up to 100-120 m min^-1.     

Two-pump-one-probe femtosecond studies of Ni(II) porphyrins excited states

Dual excited states of nickel(II) meso-tetra(4-sulfonatophenyl)porphyrin (NiTPPS) and nickel(II) meso-tetraphenylporphyrin (NiTPP) have been investigated by two-pump-one-probe transient absorption spectrometry. By dual excited states, we mean molecular entities that have absorbed two photons to generate molecular states with electronic excitation in two distinct regions of metalloporphyrin. Two successive pulses of 400 and 550 nm were used for excitation. The first pulse (400 nm) produced an S2 state of the porphyrin pi-system, which deactivated to give rise to an S1 state and subsequently produce a metal-centered (d,d) state. The second (550 nm) pulse selectively targeted an S0 --> S1 transition of those molecules having an excited metal center and was delivered to the sample approximately 40 ps after the first excitation event. At this time, the ground state of the tetrapyrrole pi-system was already regenerated and the excitation was localized at the metal center. The kinetic profiles of the NiTPPS transients in DMSO revealed biexponential decays with time constants of 0.6 and 4 ps. Photoexcitation of NiTPP in toluene and NiTPPS in water resulted in similar behavior. A mechanism for the Ni(II) porphyrin dual excited state deactivation involving the formation of an intramolecular charge transfer state has been proposed.     

In Situ Renewal of Working Surfaces of Solid Indicator Electrodes and Their Use in Electroanalysis

The design of a device for the rapid regeneration of the indicator electrode surface in a test solution is discussed. The results of testing this device are presented. The device allows obtaining reproducible areas and properties of the surfaces of solid indicator electrodes by mechanically cutting 0.1–5-μm surface layers. The best reproducibility of these parameters is attained when a hexanite-R cutter is used. The serviceability of the cutter is more than 10⁵ cuts. The high-quality renewal of electrode surfaces is achieved by cutting a 4– 5-μm layer of metallic (Pt, Ag, Au, Cu, Cd, Zn, Co, Ni, etc.) electrodes and a 0.1–1.5-μm layer of graphite and graphite-based electrodes. Optimum tool angles of the cutter for all types of solid electrodes are selected. Long-term tests of the developed technique for the mechanical renewal of electrode surface confirm that the electrode surface area is well reproducible in the series of 10⁴ measurements of the analytical signal (RSD = 0.2–0.6%). Examples are given that point to the enhancement of the electrochemical activity of the surfaces of some electrodes renewed in situ in a solution without their exposure to air. It is shown that the mechanical regeneration of the electrode surface in the solution is the main condition for depositing metals under high-voltage (up to 1000 V) conditions for electroaccumulation. The advantages of the proposed technique are exemplified by determining the concentrations of cations, anions, and some organic substances by direct and stripping voltammetry. __________ Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 12, 2005, pp. 1284–1295. Original Russian Text Copyright ? 2005 by Skvortsova, Aleksandrova, Tarasova, Kiryushov, Zamyatin.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

Measuring fluence of fast neutrons with planar silicon detectors

The results of measurements of 1-MeV (Si) equivalent fast neutron fluence with silicon planar detectors are reported. The measurement method is based on the linear dependence of the reverse detector current increment on the neutron fluence: ΔI = α _I × Φ × V. This technique provides an opportunity to measure the equivalent fluence in a wide dynamic range from 108 to 10¹⁶ cm^–2 with an unknown neutron energy spectrum and without detector calibration. The proposed method was used for monitoring in radiation resistance tests of different detector types at channel no. 3 of IBR-2 and for determining the fluence of fission and leakage neutrons at the KVINTA setup.