Natural and artificial radioactivity levels of greenhouse soils and relations with soil properties

Journal of Radioanalytical and Nuclear Chemistry - In this study, natural (226Ra, 232Th, 40K) and artificial (137Cs) radionuclide activity concentration levels of 63 greenhouse soils collected from...     

Further investigation on the formation mechanisms of (NH4)2SiF6 synthesized by dry etching technique

The validity of two formation mechanisms of ammonium silicofluoride (ASF), which are proposed to take place when a silicon surface is exposed to the vapor of HNO₃/HF acid mixture is investigated. Of the two proposed mechanisms regarding the synthesis of ASF on silicon surface, validity of the first predicting the release of hydrofluosilicic acid (H₂SiF₆) at the intermediate stage is examined by FTIR spectroscopy and the second mechanism suggesting O₂ release is investigated using the Winkler technique. IR absorbance bands of SiF₆²⁺ are observed on the fresh samples prepared at low (1/100) HNO₃/HF volume fractions. No significant amount of oxygen is detected during the synthesis of ASF films on silicon surface by dry etching technique. These two observations together provide firmer support for the validity of the second mechanism.     

Acoustic beam splitting in a sonic crystal around a directional band gap

Beam splitting upon refraction in a triangular sonic crystal composed of aluminum cylinders in air is experimentally and numerically demonstrated to occur due to finite source size,which facilitates circumvention of a directional band gap.Experiments reveal that two distinct beams emerge at crystal output,in agreement with the numerical results obtained through the finite-element method.Beam splitting occurs at sufficiently-small source sizes comparable to lattice periodicity determined by the spatial gap width in reciprocal space.Split beams propagate in equal amplitude,whereas beam splitting is destructed for oblique incidence above a critical incidence angle.     

Thermal analysis of thin layer boilover

A mathematical model is developed to simulate the thin layer boilover phenomenon. This model takes into account convective currents as well as conduction and radiation absorption through the fuel layer and is resolved numerically employing a scheme of Runge–Kutta, combined with the numerical method of lines. Solutions of the model showed a good agreement with the experimental data, both from this work and by other authors, demonstrating the importance of the convective currents. The model provided velocities of these currents, of the same order of magnitude as the values reported in the technical literature. Thickness of the remaining fuel and the interface temperature are correctly calculated by the model, allowing the prediction of the time required for the boilover to start.     

Developing prospective teachers’ covariational reasoning through a model development sequence

Forming part of a wider research study, the current study investigated prospective middle school mathematics teachers’ ways of covariational reasoning on tasks involving simultaneously changing quantities. As the introductory theme of a larger unit on derivative, a model development sequence on covariational reasoning was designed and experimented with 20 participants in a mathematical modeling course offered to prospective teachers. The participants’ developing abilities of covariational reasoning were documented under three categories: (i) identifying the variables, (ii) ways of coordinating the variables, and (iii) ways of quantifying the rate of change. The results revealed significant improvement in the prospective teachers’ ways of identifying and coordinating the variables, and in quantifying the rate of change. Moreover, the results indicated that preference for a particular way of thinking in identifying and coordinating the variables determined the prospective teachers’ way of quantifying the rate of change and thereby their level of covariational reasoning.     

Effects of gamma irradiation on the shoot length of Cicer seeds

The effects of radiation on the shoot and root lengths of germinated seedling of irradiated seeds of Cicer species, i.e. three kabuli types and four desi types of cultivated chickpea (Cicer arietinum Ladiz.) and 2 annual wild types (C. reticulatum Ladiz. and C. bijugum K.H. Rech.) were investigated. The seeds were irradiated with a ⁶⁰Co gamma source using 0, 200, 300 and 400 Gy doses at 1.66 kGy h⁻¹. At 200 Gy minor effects could be observed, but at 400 Gy an obvious depression of shoot length was observed. The kabuli types were more affected than the desi ones. The critical dose that prevented the shoot and root elongation varied among species and also ranged from genotypes to genotype within species.     

Realization of the transformation operator in the Jansen—Byers brown perturbation theory for exchange interactions

We obtain the general form and exhibit simple expressions for the transformation operator in the Jansen—Byers Brown exchange perturbation theory, without the use of an orthonormalization process.     

Technological significance of sol-gel process and process-induced variations in sol-gel materials and coatings

A significant aspect of sol-gel technology is the capability it provides to affect the substructure of materials by controlling the nature and the kinetics of chemical reactions. This capability allows us to produce novel materials, design unique molecular and pore morphologies, circumvent high-temperature reactions, and modify material properties. The modifications include strongly thermodynamic-dependent high-temperature properties such as sintering, crystallization, and viscosity in glass and ceramic materials. A particularly exciting area for investigation is the optical-electronic field, where a significant dependence of electro-optical properties and photosensitivity on process-induced molecular-structural variations occurs. Understanding the basis for the creation of structural variations in sol-gel processes should have significant impact on the technologies and systems that use these materials. In this article, some fundamental aspects of alkoxide-based, sol-gel processes and thermochemical bases for process-induced structural variates are discussed.