Low Level Measurement of Plutonium Content in Bioassay Using SSNTD Alpha-Spectrometry

Solid state nuclear track detectors (SSNTD) find wide application in registration of different types of ionization irradiation due to excellent features: low cost, compactness, passivity and possibility of long term exposure for low activity measurements. One of the most shortcomings is in complex processing of the detector surface and following image analysis. However, present methods which allow reconstruction of track ranges and particle energies are intensively being developed. A developing trend in SSNTD alpha-spectrometry uses automated scanning microscope systems and specially designed mathematical software. Several parameters obtained from the analysis of etched tracks indi information about alpha-particle ranges in detector. The possibility to use some parameters (minor axis m and track end diameter d) for the spectrometry has been reported earlier. Intercomparison of SSNTD with semiconductor detectors (SCD) for ^238,239Pu content in bioassay within the interval 10^-3 to 1 Bq has been carried out. This comparison has demonstrated a good coincidence between these independent radiometric methods. A perspective of SSNTD use for spectrometric determination of low level activity is discussed. The background level playing a main role in low level detection has been also estimated. Influence of radon and thoron has been found as insignificant.     

Dynamic system of an engine with spatially rocking links: a mathematical model

A mathematical model of a diesel with swashplates is proposed. The results of studying its design, kinematics, and dynamics are presented. The kinematic chain of the statically determinate mechanism of the engine is schematized. The kinematic relations are obtained taking into account the presence of Hooke’s joints and swashplates. A mathematical model of the dynamic system of the engine is described. A numerical example is given. The kinematics and dynamic processes of the engine are studied     

Modeling mechanical systems of variable structure

Institute of Mechanics, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Prikladnaya Mekhanika, Vol. 25, No. 6, pp. 81–88, June, 1989.     

Selecting the Coefficients of Sliding Friction in the Problem on Frictional Interaction of Three Solids

The choice of the coefficients of sliding friction in the static equilibrium problem for a system of three solids with friction at two points is discussed. This system simulates the mechanism of gravitational seismic isolation of a solid. It is shown that the coefficients of friction must be identical at both points of frictional contact irrespective of the type of the material and surface finish. A formula for the balanced coefficient of friction is derived based on experimental data     

The kinetic limitation of anti-stokes luminescence of Er3+ and Yb3+ doped infrared upconversion materials

Infrared-to-visible wave-length conversion in the Yb³⁺−Er³⁺ doped phosphors system has been described by a simple three level model based on two ions mechanism. The excitation in the range of 900–1000 nm of an IR-photon is first absorbed by Yb³⁺ ion as a sensitizer attributed to the resonant energy transition in Er³⁺ ion from ⁴ I _3/2 → ⁴ S _15/2 and ¹ F _9/2 → ⁴ I _15/2, respectively for green and red emission. The essential energy transfer processes in this system i.e. upconversion from ⁴ I _11/2 and ¹ I _13/2, cross-relaxation from ⁴ S _3/2 and ¹ F _9/2 are taken into account. The limitations of the rate-equation approach are examined with a focus on the underlying dynamics of this rare-earth system.     

APPLICATION OF GENETIC ALGORITHM IN PARTICLE SIZE ANALYSIS BY MULTISPECTRAL EXTINCTION MEASUREMENTS

Both dependent and independent model algorithms are designed with genetic algorithm (GA) to retrieve aerosol size data from multispectral extinction measurements. Compared with the traditional dependent model algorithm, e.g., simplex, GA can locate the global optimized solution instead of local ones. As an independent model algonthm, when combined with B-splines, GA gives consistent results with Chahine and Phillip-Twomey-NNLS algorithms. Numerical simulations also show that GA has high stability and good resistance to relatively higher error levels. For a population size of 50 in the present paper, the feasible ranges for genetic operators Pc and pm are found to be [0.01, 0.5] and [0.01, 0.15], respectively, and the generation number Gen_Max should be larger than 250.     

Methanol Decomposition in a Water–Methanol Equimolar Mixture on a Nickel-Promoted Copper–Zinc–Cement Catalyst

Methanol decomposition in a water–methanol equimolar mixture is studied in the presence of a nickel-promoted copper–zinc–cement catalyst. Methanol decomposition at 200–300°C on the oxide and reduced forms of the catalyst yields a gas with an H₂/CO ratio close to two. The use of an equimolar CH₃OH–H₂O mixture under analogous conditions enables obtaining gaseous products with a hydrogen concentration up to 75 vol %.     

Weighted moments for a supercritical branching process in a varying or random environment

Let W be the limit of the normalized population size of a supercritical branching process in a varying or random environment. By an elementary method, we find sufficient conditions under which W has finite weighted moments of the form EWpl(W), where p > 1, l 0 is a concave or slowly varying function.