The possibility or even necessity of revising definitions of some of the base units of the present SI has been discussed over the past 15 years. The last General Conference of Weights and Measures (2007) recommended to redefine the kilogram, the ampere, the kelvin, and the mole using fixed values of the fundamental constants by the time of the next General Conference in 2011. This paper is a review of proposals of new definitions of units of mentioned quantities and arguments voting for particular variants of definitions. Most relevant papers for this review have been published by Metrologia, the international journal appointed at the BIPM, and many other useful pieces of information are available on www pages of the BIPM. The author notes that not only new definitions have been discussed but as well as the set of the base units of the SI. It means a replacement of the ampere by the volt or the kelvin by the joule. Decisions concerning new definitions are not made and the discussions are still open.
The paper presents results of a study concerning an AlSi7Mg alloy and the effect of subjecting the liquid metal to four different processes: conventional refining with hexachloroethane; the same refining followed by modification with titanium, boron, and sodium; refining by purging with argon carried out in parallel with modification with titanium and boron salts and strontium; and parallel refining with argon and modification with titanium, boron, and sodium salts. The effect of these four processes on compactness of the material, parameters of microstructure, and fatigue strength of AlSi7Mg alloy after heat treatment. It has been found that the highest compactness (the lowest porosity ratio value) and the most favorable values of the examined parameters of microstructure were demonstrated by the alloy obtained with the use of the process including parallel purging with argon and modification with salts of titanium, boron, and sodium. It has been found that in the fatigue cracking process observed in all the four variants of the liquid metal treatment, the crucial role in initiation of fatigue cracks was played by porosity. Application of the process consisting in refining by purging with argon parallel to modification with Ti, B, and Na salts allowed to refine the microstructure and reduce significantly porosity of the alloy extending thus the time of initiation and propagation of fatigue cracks. The ultimate effect consisted in a distinct increase of the fatigue limit value.
The text discusses the problems of sensory processing disorders (SPD) and their impact on difficulties children have at school. Individual categories of sensory processing disorders were characterized and examples of behavior of children who may have those problems were described. Certain strategies which teachers can use when working with a child with SI disorders were also offered. It should be noted that the early diagnosis of symptoms that may indicate the occurrence of sensory processing disorders, followed by apt diagnosis and therapy allow children to function properly in the school environment and positively influence their self-esteem. This in turn facilitates the process of learning and contributes future success.