D.E. Clippinger and G.J. Morris
THE use of liquid oxygen as an oxidizer for various fuels in liquid rocket propellent systems is not new. Professor Goddard used liquid oxygen in his rocket experiments and the…
Abstract
THE use of liquid oxygen as an oxidizer for various fuels in liquid rocket propellent systems is not new. Professor Goddard used liquid oxygen in his rocket experiments and the well known German V‐2 rockets used this material as an oxidizer. However, its effect on non‐metallic materials ordinarily used in rocket systems was not investigated until recent years. This investigation was prompted by phenomena which had been experienced by rocket engine and rocket aircraft manufacturers and by suppliers of the material. It was observed that when some organic materials came in intimate contact with liquid oxygen they became prone to detonation when subjected to certain impact energies. This was undoubtedly due to the formation of unstable organo‐peroxide compounds which when impacted released high levels of energy resulting in an explosion. Specifically, when liquid oxygen was accidently spilled on asphalt and inadvertently stepped on, the asphalt would often explode. Also, leather gaskets immersed in liquid oxygen and subjected to surge impact detonated with disastrous effects.
In the paper the optimization procedure of a direct current motor with a hybrid excitation has been presented. The excitation system consists of a shunt field winding disposed…
Abstract
In the paper the optimization procedure of a direct current motor with a hybrid excitation has been presented. The excitation system consists of a shunt field winding disposed around field pole and permanent magnet, both acting in parallel. The field distribution in motor for various magnet and field pole dimensions has been determined using finite element method. The flux linkage with the armature winding has been computed. Demagnetizing effect of armature current was taken into account. The optimal permanent magnet and the field pole dimensions, ensuring minimum total cost of purchase and work during assumed period of time were calculated. Motor characteristics e.g. rated torque, rated current, speed regulation limit were used as constraints. In worked up algorithm and computer program Carroll internal penalty function method was used. Some basic suggestions tor design of optimal hybrid excited dc motors with parallel permanent magnet and electromagnetic excitation are given.
M. Ndour, K. Abbaoui, H. Ammar and Y. Cherruault
Describes the use of the decomposition method for solving the differential system governing the interaction between two species, based on the Lotka‐Volterra model. The Alienor…
Abstract
Describes the use of the decomposition method for solving the differential system governing the interaction between two species, based on the Lotka‐Volterra model. The Alienor method is applied for identifying the parameters of the model, which are the intrinsic rates of natural increase of the different species and their interaction coefficients.
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I‐V characteristics of GaAs n‐i‐n structures are calculated by considering impact ionization of carriers. Impact ionization at reverse‐biased n‐i junction becomes a cause of steep…
Abstract
I‐V characteristics of GaAs n‐i‐n structures are calculated by considering impact ionization of carriers. Impact ionization at reverse‐biased n‐i junction becomes a cause of steep current rise when an acceptor density in the i‐layer is high. It is shown that an optimum acceptor density exists to keep a good isolation. Photoconduction transients of GaAs n‐i‐n structures are also simulated, and are shown to be strongly affected by existence of n‐i junctions.
In the course of development of human communities towards industrially advanced societies of today, there have been changes not only in economic conditions in the majority of…
Abstract
In the course of development of human communities towards industrially advanced societies of today, there have been changes not only in economic conditions in the majority of fields of human activity but also in the ways of providing for food, which went hand in hand with changes in living conditions. Large‐scale industrial production has brought about major changes in the way of life of the population. The development of industrial agglomerations results in a growing number of city dwellers, most of whom have no chance of producing foodstuffs of their own in kind. The distance between residential and industrial areas has been growing, the number of employed women has risen considerably. These are but a few factors affecting the way of boarding, particularly in households.
Xiaoxia Li, Xingcheng Liu and Xuemou Wu
Tables are widely used to store information. It belongs to table decision making to choose the pivotal fields or partition fields into conditions and decisions to discover their…
Abstract
Purpose
Tables are widely used to store information. It belongs to table decision making to choose the pivotal fields or partition fields into conditions and decisions to discover their causality. This paper is intended to list the basic operations to achieve the aims and to explore possible solving methods.
Design/methodology/approach
Methods, to some degree, means problem transformation. That is, a problem can be converted to another problem and then to be solved. This paper is developed to explore possible problem transformations surrounding the basic table decision operations.
Findings
The basic table decision operations can be converted to two different types of problems.
Originality/value
This paper provides formal description of the basic table decision operations and their transforming schemes so that strict mathematical proof can be used to guarantee their correctness.
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Michal Polácek and Rudolf Aroch
The commercial practice of tourism avails itself of a whole range of classical methods of research into market, its dispersion and trends, starting with statistics and ending up…
Abstract
The commercial practice of tourism avails itself of a whole range of classical methods of research into market, its dispersion and trends, starting with statistics and ending up with public opinion polls. The pattern and volume of tourism demand as well as its principal trends may be compared on the basis of international statistics that are more or less uniform. However, not even more detailed statistical observations are adequate for the formulation of long‐term marketing strategy of the given country.
Economic effects are only one aspect of the total impact of tourism. For example, the development of a tourist industry in a particular country has varying repurcussions on the…
Abstract
Economic effects are only one aspect of the total impact of tourism. For example, the development of a tourist industry in a particular country has varying repurcussions on the long term socio‐cultural, environmental and ecological development of the local community as a whole. This article examines the main non‐economic aspects of tourism in Greece.
Zhivko Georgiev and Ivan Trushev
This paper aims to analyze transient and steady state processes in series resistive capacitive-circuits when the supplied voltage is a sequence of periodic rectangular pulses. The…
Abstract
Purpose
This paper aims to analyze transient and steady state processes in series resistive capacitive-circuits when the supplied voltage is a sequence of periodic rectangular pulses. The purpose is to obtain an analytical formula for the capacitor voltage at any instant of time, both for the transient and the steady-state processes.
Design/methodology/approach
The main approach is to use a combination of differential and recurrence equations.
Findings
An analytical expression (formula) for obtaining the capacitor voltage at any instant of time has been found.
Originality/value
The results obtained are new. They are much more convenient to use than the results obtained by the Fourier series. The exposed approach can also be used in other circuits and other forms of the supplied voltage.
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K. Abbaoui, Y. Cherruault and M. Ndour
The decomposition method is used for solving differential systems in biology and medicine. A comparison is given between the Runge‐Kutta method and the decomposition technique…
Abstract
The decomposition method is used for solving differential systems in biology and medicine. A comparison is given between the Runge‐Kutta method and the decomposition technique. New relationships for calculating Adomian’s polynomials are used for solving the differential systems governing the competition between species and based on the Lotka‐Volterra model.