A basic formula of differential thermal analysis is evolved for the case when the heat transfer coefficient between the specimen cell and the reference cell is not zero. The more general formula obtained differs from the classical formula by including the parameters of the reference cell and the heat transfer coefficient between the cells. It indicates that utilization of the classical formula is not correct if heat exchange occurs between the cells. To utilize the generalized formula, additional measurements of the temperature changes of the reference material are required. However, if the time constants of the two cells are identical, the formula can be changed to assume the form of the classical formula for DTA if a correction factor is introduced which takes into account the effect of heat exchange between the cells.
With the aims of accounting for the effects of the internal thermal resistance of the sample holder on the parameters of recorded DTA curves, and of estimating the difference between the instrument with a thermally insulated sample holder and the gradientless model, a novel two-point method of differential thermal analysis has been developed. Its essence is that two thermoanalytical curves are recorded simultaneously, with the differential thermocouple at central and side positions relative to the sample. The theory of the method has been elaborated, and formulae are derived which allow quantitative estimation of the thermal resistance of the sample holder, depending on the manner of packing and on the state of the sample in the holder, and which also indicate the optimum manner of packing. If the packing is not dense and not uniform, the thermal resistance of the holder increases and the accuracy of instrument calibration at the tail-end of the differential curve decreases by 10–20%. Through introduction of a correction term into the formula, this effect can be eliminated. A basic formula is given for DTA calculation in the general case of a sample holder with non-zero internal thermal résistance.
The mathematical theory is developed for heat transfer in the cells of DTA instruments with no temperature gradient. Equations are derived for the various portions of the differential curve. The concepts of real and hypothetical base lines are introduced and rules are formulated for plotting them. Three methods are proposed for processing the curves, with and without the introduction of base lines. The physical meanings of the geometrical elements of the thermal curves and their relationship with the experimentally determined thermal quantities are elucidated. Equations in differential and integral forms are derived for the base line of the cell and the base line of the reaction.
The theory of block-type sensing units is reviewed. The two-point method of DTA is described and appropriate computation formulae are derived. The failure of the existing blocktype sensing units to conform to the assumptions of the theory is demonstrated.
The behaviour of information flows in different subfields of muticomponent polymer systems was compared for the years 1979 and 1983. The classification used enabled the maximum information on the species of polymer compositions to concisely be recorded. It was established that the information flows in the subfields of multicomponent polymer systems obeyed the law of literature scatter. In 1979 and 1983 about half of the total number of papers dealt with two species of polymer compositions: homopolymer blends and filled homopolymers. About 40% of species described in publications of 1979 did not appear either in journals or in proceedings of 1983. But new species accounted for 60% of the information flow in 1983.
The behaviour of information flows in multicomponent polymer systems over the 1979–1983 period is analyzed. It has been found that this field of science obeys general relationships valid for other established sciences. Its special features are a high concentration of information (only 9 journals) and a wide scatter of papers among a great number of peripheral journals. The doubling times for papers and journals as well as the doubling period for papers in a single journal have been determined, they are 3.2, 4.6 and 5.6 years respectively.
Complex cell walls of barley hulls contain phenolic constituents — hydroxycinnamic acids, mainly ferulic acid (3-methoxy-4-hydroxy-cinnamic acid, FA) and para-coumaric acid (4-hydroxycinnamic acid, PCA). Ferulic acid is produced via the phenylpropanoid biosynthetic pathway and is covalently cross-linked to polysaccharides by ester bonds and to components of lignin mainly by ether bonds. Various studies have consistently indicated that FA is among the factors most inhibitory to the biodegradability of plant cell wall polysaccharides. PCA is also covalently linked to polysaccharides (minor) and lignin (major), but PCA does not form the inhibitory cross-linkages as FA does. It is considered to represent plant cell wall lignification. The objective of this study was to determine the genotypic variation and magnitude of difference in the concentration of the hydroxycinnamic acids in terms of FA and PCA as well as their ratios in barley hull and seeds in sixteen varieties of barley collected during three years. These data will be correlated to barley nutrient availability in future study. The barley varieties included CDC Cowboy, Valier, TR251, Newdale, RCSL97, KXN/TLN-147 (AU), WABAR2160 (AU), Harrington, CDC Copeland, CDC Kendall, AC Metcalfe, CDC Dolly, McLeod, CDC Bold, CDC Helgason and CDC Trey. The focus of this study was on ferulic acid because of its inhibitory effect on rumen degradation and digestion which are highly related to nutrient availability in animals. The results showed significant differences (P < 0.01) a mong the barley varieties in ferulic acid and p-coumaric acid and their ratio. Whole barley seed contained higher (P<0.05) ferulic acid concentration than p-coumaric acid, ranging from 509 to 679 μg/g DM for ferulic acid and 131 to 345 μg/g DM for p-coumaric acid. The ratios of ferulic acid to p-coumaric acid ranged from 1.8 to 3.9. The ferulic acid concentration in hull was higher (P < 0.05) than that in whole seed, ranging from 2,320 to 4,206 μg/g DM. Percentage of ferulic acid content in hull and dehulled seed ranged from 38 to 70% and 30 to 62%, respectively. Growth year affect affected the hydroxycinnamic acid profiles in barley seed and hull. In conclusion, there were large differences in the ferulic acid and para-coumaric acid among the barley varieties indicating genotypic variation. Harrington contained highest and Valier contained lowest FA in whole seed. Barley TR251 contained lowest % of FA content in the hull and highest % of FA content in the dehulled seed. Future study is needed to understand the relationship between the hydroxycinnamic acid profile in barley seeds and hull and nutrient utilization and availability of barley in animals.
Thermal insulation and fire protection have been a point of interest and discussion for several decades. Due to its excellent
performances, basalt fiber has been widely used in the fields of thermal insulation and fire protection. The morphological
structure and thermal stability of continuous basalt fiber were analysed using CH-2 projection microscope, scanning electron
microscope (SEM) and thermogravimetry (TG). In order to evaluate the thermal radiation protective performance when exposed
to fire environment, the spectral reflectances of nonwoven fabrics with different thicknesses were evaluated by ultraviolet-visible-near
infrared (UV–Vis–NIR) spectrophotometer analysis. The jointly analysis of TG and UV–Vis–NIR spectrophotometer revealed that
the basalt fiber exhibits good thermal stability, and the nonwoven fabrics present excellent thermal protective performance.
The total efficiency of γ-ray detection by Ge(Li) semiconductors is calculated for the energy range 0.1 to 10 MeV, for cylindrical
detectors with radii from 0.25 cm to 2.5 cm and thicknesses from 0.1 cm to 1 cm, at distances between the source and detector
ranging from 2 cm to 20 cm.
Authors:V. Pchelkin, M. Sviderskii, L. Grinberg, Yu. Burmistenko, and Yu. Feoktistov
On a présenté les méthodes d'analyse par activation de petites concentrations d'Au, Ta et Sc dans des roches, des minerais
et des minéraux. On a utilisé comme moyen d'activation un réacteur nucléaire et un accélérateur linéaire puissant. On a réalisé
ainsi les réactions (γ, γ) pour la détermination de Au et (γ,n) pour celle de Ta. Dans un flux de neutrons thermiques de réacteur,
on a effectué la détermination de Au, Sc, Ta par réactions (n,γ) à l'aide de séparation radiochimique des isotopes correspondants.