Electrical potential technique for monitoring subcritical crack growth at elevated temperatures

The electrical potential technique has been successfully used to monitor crack extension under fatigue as well as sustained loading at elevated temperatures in the presence of gross creep deformation. Calibration curves for actual crack extension vs change in electrical potential were determined for two specimen geometries, namely the compact type (CT) and the center crack tension (CCT) type, for an ASTM, grade A470 class 8 steel at 538°C (1000°F) and for a type 304 stainless steel at 594°C (1100°F).

A normalizing factor for expressing crack extension has been derived for the CT specimen. This factor accounts for changes in calibration due to small differences in initial crack length and, it also makes the calibration curve independent of the test temperature and material. Hence, the calibration curves presented herein are applicable to other materials and temperatures provided the specimen geometry and size is the same and the current input and potential leads are also located at the same position.     

The burning of large pool fires

A non-intrusive method for obtaining the spatial distributions of radiative properties (i.e.) absorption-emission coefficients and radiation temperatures) in pool fires is described. The method consists of measuring the lateral transmittance and radiance of the fire and performing an Abel inversion on the measurements to obtain absorption-emission coefficients and local radiation temperatures in the fire. Local radiative properties so obtained are used to calculate the flame radiation flux—the dominant heat transfer mode —to the pool surface. The computed flux is in good agreement with the flux inferred from experimentally measured burning rates of the fire. These experiments are performed on a 0.73 m diameter PMMA pool fire. The results presented here show that large pool fires tend to be significantly non-uniform in temperature and species concentrations and the non-uniformities play an important role in determining the burning rate of these fires.     

A thermochemical approach to the gas-phase reduction of metal sulphates

The reduction of different metal sulphates by hydrogen occurs at different temperatures and can lead to a variety of products. It has been shown that the starting temperatures for the reduction of several sulphates are directly related to the magnitude of their (exothermic) heats of formation per equivalent. The thermochemical data also provide a basis for the interpretation of the relative thermal stabilities (under nitrogen atmosphere) of several metal sulphates. A consideration of the appropriate heat of formation values can also be useful in understanding the different reduction products obtained for different metal sulphates. Finally, the reduction behaviour of some binary metal sulphates is also consistent with the thermochemical data.     

Some fundamental analogies between solid,molten and aqueous materials: application of the concepts of energy levels and the band theory of solids

An interaction of electrochemical ideas with the approaches of solid state physics provides some interesting analogies and themes in which certain aspects of electrolyte solutions, solid semiconductors and ionic liquids can be discussed in a somewhat inter-related manner. Some of the fundamental properties of this wide range of materials (solid semiconductors, molten salts or aqueous (electrolyte) solutions) may be unified into a loose theme derived from the general notions of the band theory of solids and its analogue in electrolyte solutions, namely, the electron and proton levels of electrolytes. The concepts which would describe the intermeshing behaviour of these materials will be derived from: the band theory of semi-conductors; Gurney's ideas on the occupied and vacant proton levels in electrolyte solutions; Rose's approach to the electron energy levels in solids and electrolytes; Fuller's views on the conceptual analogies between semiconductors and electrolyte solutions; interpretation of molten salts put forward by Bockris and co-workers; and, finally, the industrial applications of Gurney's ideas made by Vermilyea in his interpretations of the corrosion of aluminium in water and the effect of various inhibitors on this corrosion reaction.     

A two-pass solar air heater

An air heater, in which the air first flows between metallic and cover plates and is then made to flow between two metallic plates in opposite direction, is discussed theoretically. The governing equations of the model are solved explicitly under suitable conditions. The measured values of the solar insolation and ambient temperature are represented by Fourier series. The effects of collector length and flow rate have been studied. The air heater in this mode of operation is more efficient than one in which air flows between two metallic plates in the same direction, provided the plate length is less than 5 m.     

Relationship between activation energies for the thermal oxidation of metals and the semiconductivity of the oxides

The activation energies for the thermal oxidation of metals appear to be inversely related to the band gaps, heats of formation per equivalent and the electronic conductivity of the oxides formed. An attempt is made to develop the theoretical significance of these correlations in the context of a general discussion of some fundamental aspects of the thermal and the anodic oxidation of metals.     

Register allocation via coloring

Register allocation may be viewed as a graph coloring problem. Each node in the graph stands for a computed quantity that resides in a machine register, and two nodes are connected by an edge if the quantities interfere with each other, that is, if they are simultaneously live at some point in the object program. This approach, though mentioned in the literature, was never implemented before. Preliminary results of an experimental implementation in a PL/I optimizing compiler suggest that global register allocation approaching that of hand-coded assembly language may be attainable.