scholarly journals Chain character of vacancy-type defects in silicon

1990 ◽  
Vol 41 (13) ◽  
pp. 8630-8642 ◽  
Author(s):  
E. G. Sieverts ◽  
M. Sprenger ◽  
C. A. J. Ammerlaan
Keyword(s):  
Chain Character

scholarly journals A theory of the combustion of hydrocarbons

1935 ◽  
Vol 150 (869) ◽  
pp. 36-57 ◽  
Keyword(s):  
Induction Period ◽  
Kinetic Data ◽  
Analytical Data ◽  
Inert Gases ◽  
Original Form ◽  
Comprehensive Theory ◽  
Slow Combustion ◽  
Chain Character ◽  
Energy Chain ◽  
First Time

A comprehensive theory of the combustion of hydrocarbons must describe in detail all the analytic and kinetic data. Up to the present no such theory has been proposed, for though the hydroxylation theory of Bone and his school has been very successful in the former field, it is inadequate in its original form to take account of the latter. In the present paper it is shown that a comparatively small modification, involving the introduction of the conception of chain propagation by free radicals, remedies the earlier deficiency and makes possible for the first time a detailed description of the widely varied phenomena of combustion. The work of Egerton, Hinshelwood, Haber, Semenoff and others has led to the recognition that both rapid and slow combustion are autocatalytic in character, the reaction being propagated through the gas from certain initial centres, so that from every centre started by the primary mechanism, a great many molecules of hydrocarbon are oxidized. The first attempt to interpret the chain character in terms of a concrete theory is embodied in the suggestion of Egerton who has extended the peroxidation theory of Callendar to include an energy-chain mechanism by way of which reactivity is handed on from the active products (peroxides) to new reactant molecules. This theory and its various modifications, however, is unsatisfactory in more than one kinetic aspect, the effect of inert gases in particular being the reverse of the deactivation to be expected for an “energy” chain. Moreover, the peroxidation theory is not reconcilable in all respects with the analytical data, for while the induction period has been interpreted as a period of peroxide building no evidence of any such peroxide formation at this stage has been established, nor is the induction period affected by the addition of any such bodies. There thus arises the need of some further attempt to bring the analytic and kinetic data into relation with one another and in the hypothesis developed below, which we shall call the “atomic chain hypothesis,” it is believed that we have a simple explana­tion which encompasses both the analytical and kinetic results in an adequate manner.

The pyrolysis of acetylene at temperatures from 500 to 1000 °C

1964 ◽  
Vol 280 (1380) ◽  
pp. 139-152 ◽  
Keyword(s):  
Triplet State ◽  
Underlying Mechanism ◽  
Gaseous Product ◽  
Polymer Chains ◽  
Order Kinetic ◽  
Initial Product ◽  
Ambient Temperatures ◽  
Temperature Range ◽  
Gaseous Products ◽  
Chain Character

Several features of the pyrolysis of acetylene in the temperature range 500 to 1000 °C suggest that the underlying mechanism is the same as that in operation at both lower and higher temperatures. Thus the rate of consumption of acetylene obeys a second-order kinetic law and is little affected by additions of the gaseous products; the observed velocity constants agree closely with those expected if a single mechanism were in operation over the whole temperature range 350 to 2500 °C. The analytical results show conclusively that the sole initial product of the reaction is vinylacetylene. Diacetylene appears to be formed by heterogeneous decomposition of vinylacetylene and this reaction can occur at ambient temperatures in the presence of carbonaceous deposits. Methylacetylene and benzene probably arise from the further reaction of C 6 species which are formed during the building-up of polymer chains. Methane is the predominant final gaseous product of the reaction at the temperatures investigated. A mechanism is proposed which accounts for both the chain character of the reaction and the apparent existence of equilibria. It appears that acetylene is first converted to the triplet state by a surface reaction. This initial stage is then followed either by the production of C 4 and subsequent species in the triplet state by a series of step-wise reactions involving further acetylene or by the regeneration of stable species as a result of reaction, at a surface, of the corresponding excited species.

scholarly journals Features of the Innovative Model of Economic Development and the Growing Role of Education Therein

2020 ◽  
Vol 9 (512) ◽  
pp. 56-64
Author(s):  
I. H. Khanin ◽  
◽  
V. S. Bilozubenko ◽  
S. Y. Shablii ◽  
◽  
...  
Keyword(s):  
Economic Development ◽  
Structural Changes ◽  
Innovation Process ◽  
Global Trends ◽  
Modern Economy ◽  
New Knowledge ◽  
Innovative Model ◽  
Chain Character ◽  
Innovation Model

The growing importance of innovations in the economy has turned them into a more important factor in production and consumption, structural changes, economic dynamics, competitiveness, and social development. This has gained a paradigm importance and has led to the emergence of an innovative model of economic development, the peculiarities of which being the topic that the article is concerned with. Taking into account the dependence of innovations on the generation and dissemination of new knowledge, the article emphasizes the critical importance of the productivity of science and the quality of education. This is confirmed by global trends and finds a manifestation in the development strategies of the countries and companies. In this context, a modern understanding of innovations and the basis of their emergence, which is connected with knowledge and creativity, has been closer defined. The authors characterize the main features of innovation, in particular: cumulativeness, chain character, integration of practical and theoretical knowledge, duration of «maturation» and emergence of innovation, uncertainty, collectivity, uneven appearance in time and concentration in space, propensity towards conflict. A vision of the process of developing innovations by stages covered by system management is proposed. The main models of emergence of innovation together with the model of innovation process (the model of extraction through demand (market); the model of «needs seekers»; the model of «readers of market information»; the model of technological nudging; the cyclical model of innovations; the model of open innovations; the chain and interactive model of innovation process; the innovative model of «funnel»; the network model of innovation) are described. A number of features of the innovative model of economic development are allocated: recognition of innovation as the most important factor of economic growth; constant interaction of production, science and market, focused on the development of innovations; defining role of human capital; structural changes in the system of social production; domination of the innovative nature of competition in the modern economy; development of innovative entrepreneurship. On the basis of the formation of an innovative model of development, the growing role of science and education, the modern economy is characterized as an economy of knowledge; the main points of its concept are considered. An increase in the influence of education in the innovation model of the economy in terms of generating and disseminating new knowledge in order to intensify innovation is substantiated.

The thermal decomposition of aromatic compounds - I. Chlorobenzene

1954 ◽  
Vol 224 (1158) ◽  
pp. 308-321 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Aromatic Compounds ◽  
Reaction Vessel ◽  
Inert Gas ◽  
Unimolecular Reaction ◽  
Chain Reaction ◽  
Homogeneous Process ◽  
Carbon Compounds ◽  
Chain Character ◽  
Limiting Value

The thermal decomposition of chlorobenzene has been studied in the temperature region 720 to 800° C. The decomposition is a predominantly homogeneous process and leads to the production of approximately one molecule of hydrogen and one molecule of hydrogen chloride for every molecule of chlorobenzene decomposed. No gaseous carbon compounds are formed, and all the combined carbon and the remaining hydrogen are deposited on the walls of the reaction vessel as a hard, shiny, graphite-like solid. The structure of this deposit was examined by electron diffraction and compared with those produced by pyrolysis of other organic compounds. The thermal decomposition of chlorobenzene is kinetically composite. The partial chain character of the reaction is indicated by the lowering of the decomposition rate to the same limiting value on addition of both nitric oxide and ammonia. It is confirmed by the acceleration produced by an inert gas and by the retardation caused by an increase in the surface. The mechanism of the chain reaction is considered, and a possible chain cycle is proposed. The nature of the fully inhibited reaction is also discussed, and though the evidence is to some extent conflicting it is concluded that it is probably a unimolecular reaction.

scholarly journals The Snakelike Chain Character of Unstructured RNA

2014 ◽  
Vol 106 (2) ◽  
pp. 283a
Author(s):  
David R. Jacobson ◽  
Dustin B. McIntosh ◽  
Omar A. Saleh
Keyword(s):  
Chain Character

Introduction

2005 ◽  
Author(s):  
James E. Mark ◽  
Harry R. Allcock ◽  
Robert West
Keyword(s):  
Solid State ◽  
Main Chain ◽  
Modern Technology ◽  
Molecular Characteristics ◽  
Molecular Weights ◽  
Film Forming ◽  
Chain Character ◽  
Repetitive Structure ◽  
The Relationship ◽  
Long Chain

A polymer is a very-long-chain macromolecule in which hundreds or thousands of atoms are linked together to form a one-dimensional array. The skeletal atoms usually bear side groups, often two in number, which can be as small as hydrogen, chlorine, or fluorine atoms or as large as aryl or long-chain alkyl units. Polymers are different from other molecules because the long-chain character allows the chains to become entangled in solution or in the solid state or, for specific macromolecular structures, to become lined up in regular arrays in the solid state. These molecular characteristics give rise to solid-state materials properties, such as strength, elasticity, fiber-forming qualities, or film-forming properties, that are not found for small molecule systems. The molecular weights of polymers are normally so high that, for all practical purposes, they are nonvolatile. These characteristics underlie the widespread use of polymers in all aspects of modern technology. Attempts to understand the relationship between the macromolecular structure and the unusual properties characterize much of the fundamental science in this field. Polymers are among the most complicated molecules known. They may contain thousands of atoms in the main chain, plus complex clusters of atoms that form the side groups attached to the skeletal units. How, then, can we depict such molecules in a manner that is easy to comprehend? First, an enormous simplification can be achieved if we remember that most synthetic polymers contain a fairly simple structure that repeats over and over down the chain. This simplest repetitive structure is known as the repeating unit, and it provides the basis for an uncomplicated representation of the structure of the whole polymer. For example, suppose that a polymer consists of a long chain of atoms of type A, to which are attached side groups, R. The polymer chain can be represented by the formula shown in 1.1. The two horizontal lines represent the bonds of the main chain. The brackets (or parentheses) indicate that the structure repeats many times. The actual number of repeating units present is normally not specified, but is represented by the subscript, n.

Phosphatidylcholine-Cerebrosides Interactions: Influence of Cerebroside Acyl Chain Character

1986 ◽  
Vol 132 (1-2) ◽  
pp. 189-198 ◽  
Author(s):  
J. M. Collins ◽  
W. T. Lis ◽  
L. J. Lis
Keyword(s):  
Acyl Chain ◽  
Chain Character

scholarly journals The Snakelike Chain Character of Unstructured RNA

2013 ◽  
Vol 105 (11) ◽  
pp. 2569-2576 ◽  
Author(s):  
David R. Jacobson ◽  
Dustin B. McIntosh ◽  
Omar A. Saleh
Keyword(s):  
Chain Character

scholarly journals The kinetics of the reaction between hydrogen and nitrous oxide. Part II

1934 ◽  
Vol 146 (859) ◽  
pp. 737-759 ◽  
Keyword(s):  
Nitrous Oxide ◽  
Wave Length ◽  
Kinetic Method ◽  
Strong Support ◽  
Chain Process ◽  
Absorption Region ◽  
Chain Character ◽  
A Chain ◽  
The Individual ◽  
Low Pressures

An analysis of the mechanism of the thermal hydrogen-nitrous oxide reaction in silica vessels by the kinetic method has shown that it is a chain process. The experiments were confined to a comparatively narrow pressure range and the evidence for chain propagation, although quite definite, required confirmation. The present paper is therefore concerned with the kinetics under a much wider variety of conditions. First, the experiments have been extended to pressures below 30 mm; second, photochemical methods have been employed to she more light on the individual steps of the reaction and to demonstrate unequivocally its chain character; third, in view of the close similarity of the hydrogen-nitrous oxide and hydrogen-oxygen reactions, a detailed study has been made of the effect of small amounts of oxygen on the former reaction. The results of these experiments all lend additional strong support to the chain hypothesis. Small alterations to the apparatus were made. A glass spring gauge was employed for measuring low pressures. One end of the furnace was provided with quartz lens in order to focus the light from the mercury lamp on the reaction bulb; the cathode of the lamp was water cooled. Arrangements were also made for inserting a hollow silica cell between the lamp and the lens so that filters could be used for controlling the intensity and wave-length of the light reaching the bulb. Direct photo dissociation of the nitrous oxide molecule was not attempted since ( a ) absorption of photochemically active light at low pressures in small bulbs is not complete, ( b ) the intensity of the lines of the mercury arc in the absorption region of nitrous oxide is weak. Recourse was therefore made to mercury sensitization in spite of a little additional complication.

Sign in / Sign up

Export Citation Format

Share Document