Navigational facilities for relational data base

Charles Bachman's great idea of navigation in a data base is applied to the relational data model. This idea, understood as a way of user thinking, is formulated in such a manner, that no physical concepts are introduced to the user's awareness. Thus the demanded level of data independence is not reduced.A concept of “navigational statement” is defined. The navigational statements may be used to improve other relational languages, for example SEQUEL. It is shown that navigational statements simplify the grammar structure of language expressions and make them shorter and more readable. Elliptic (incomplete) navigational statements are also defined. Such statements may be regarded as a good tool for the casual user.This paper may be viewed as a (not necessarily complete) review of possibilities related to the idea of navigation in a relational data base.     

The mechanism of dry friction of polyoxymethylene against steel

The mechanism of friction between polyoxymethylene and steel was investigated. The coefficient of friction was determined, and the effects of the hardness of the steel, the roughness of the sliding surface, the temperature, the relative sliding velocity and the contact pressure were examined. Additional investigations were carried out to explain the mechanism of friction between the polymer and steel. Structural changes in the friction surfaces were investigated by microscope examination. Five fundamental types of friction were identified and are discussed.     

Study on the protective role of selenium against cadmium toxicity in lactic acid bacteria: an advanced application of ICP-MS

In this work, Lactobacillus casei rhamnosus were obtained from the commercial product of fermented milk and possible antagonistic effect of selenium (as sodium selenite) against cadmium toxicity was studied. The bacteria capability to incorporate Se was demonstrated: after 1 week exposure to Se(IV), its total concentration in the freeze-dried biomass was 405+/-28 microg/g (7.4+/-0.8 microg/g in control). In the presence of Se(IV) and Cd(II), the bacterial growth and cell viability were improved and lipid peroxidation less marked with respect to bacteria exposed to Cd(II) alone. The distribution of Se and Cd in molecular mass fractions of bacteria extracts was investigated by size exclusion chromatography with diode array and ICP-MS detection. The results obtained suggest that the antagonistic effect of Se is due to lower incorporation of cadmium at a high molecular mass (MM<600 kDa). Slightly different distribution of elements in the fractions of MM<40 kDa suggests the formation of new chemical species involving Cd and Se in bacteria exposed to Cd(II)+Se(IV) as compared to those exposed to Cd(II) alone. The study illustrates the high utility of atomic spectrometry to critically inform molecular questions that could be important in the industrial processes based on bacterial activity.     

Powder solders for hard soldering of aluminium and its alloys

In this paper, the possibilities for forming non-circular pulleys using laser cutting techniques and cutting techniques using water jets with abrasive materials are described. Research on laser cutting with use of gases for formation of carbon steel and acid-resistant steel pulleys is also discussed. The advantages of water jet cutting of non-circular pulleys are shown, and the methodology for measuring machined pulleys with a coordinate measuring technique is also presented. Use of computer-aided design systems with a range of software enabling automation of CNC contour saw control and optimization processes for formed elements spacing are all also discussed.     

Condensing Heat Exchanger

The paper shows a method of designing a heat exchanger recovering heat from the condensation of water vapour contained in flue gases. A heat exchanger condenses water vapour and SO2 （sulphur dioxide） in the presence of inert gases （CO2, CO, N2, O2） contained in flue gases. A mathematical model and a sample design of a heat exchanger were presented. The heat exchange is capable of recovering from a dozen or so to several dozen percent of heat from flue gases escaping into the atmosphere. A second advantage of the heat exchanger is the possibility to reduce the emissions of SO2 considerably. Depending on the parameters, it can be even a sevenfold reduction in the emissions. The main mathematical tool used for designing the condensing heat exchanger is the Colburn-Hougen method. The authors omitted that part of the method which requires iterative calculations. The Mollier diagram was used instead.     

The technique and analysis of the process of separation and cleaning grain materials

In the process of pneumatic separation, the aerodynamic properties of particles such as their critical velocity, are used.A pneumatic separator was designed that allowed a wide range of control parameters to be used.The essential factors affecting the course of the separation process were identified and a theoretical correlation between these factors and the separation efficiency were determined.The main aim of the study was to analyse the separation process in an air stream of broken lupine seeds, chiefly involving theoretical considerations of movement and behaviour of mixture particles in a pneumatic canal. Investigations and observations gave ground for an attempt at deriving a movement equation of particles in an unrestrained, uniform air stream.The equations obtained can be used for calculating the parameters of particle movement in pneumatic canals. The velocities of air stream, then, can be a few times higher than the critical velocity/convection/of individual particles. While working out the above problems the following points were considered: on the one hand, possibilities of obtaining the greatest outcome from the separation process and on the other, reducing the losses of valuable material in the discarded lot to a maximum.     

Temperature Distribution in a Single Sphere Dried with Microwaves and Hot Air

This paper examines the temperature distribution within a spherical particle of the porous material dried with microwaves and hot air. Experimental results are compared with results obtained from a simple mathematical solution, where the problem of the internal electric field pattern was considered to be either uniform or non-uniform.     

Non-contact methods of measuring moisture concentration in external layers of building partitions. I—The influence of geometrical microstructure on the kinetics of moisture condensation on glass surfaces

This paper presents the results of the larger study on the potential application of laser radiation for the detection of phase transition processes. The proposed experimental method allows a dynamic study of the phenomena without mechanical intervention. This seems to be the best practical solution particularly when the access for the other methods is very restricted. The investigations give an evidence of the strong relationships between the rapid growth of water vapour condensate and the roughness of the surface. Condensation process therefore can be modified by a careful design of the geometrical structure of surface.