Analysis of Field Data on Computer Failures

This paper emphasizes the importance of making field measurements for effective and realistic dependability evaluatians.Two examples are given,both based on real data from IBM mainframes.The first evaluates the imnact of the operating environment on system failure characteristics and the second shows how an accurate model depicting this interaction can be extracted from real data.     

Doppler-broadened positron annihilation studies in Y-Ba-Cu-O,Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O superconductors

Doppler-broadened annihilation radiation spectra have been measured as a function of temperature from 77 K to 300 K, for several high temperature oxide superconductors viz single-phase YBCO, single- and mixed-phase Tl-Ca-Ba-Cu-O and Bi-Ca-Sr-Cu-O compounds. The temperature-dependent parameters extracted respond to a change at the onset of superconducting transition. The observations point to involvement of oxygen valence electrons at the onset of superconducting transition. Also a possible structural change and/or increase in electron density at the oxygen vacancy/defect sites seem to accompany the transition. In addition, the parameters derived are seen to be sensitive to the presence of more than one superconducting phases in mixed phase samples.     

Effect of α-amylase addition on fermentation of idli—A popular south Indian cereal—Legume-based snack food

Idli is a fermented breakfast food widely consumed in Southern India. It is liked by people mainly due to its sensory attributes such as mouthfeel, appearance, taste and aroma. Fermentation time of the batter varies from 14 to 24 h with overnight fermentation being the most frequent time interval. Reduction in the fermentation time of the idli batter is of great commercial significance for large-scale idli production and this can be potentially achieved by addition of enzymes externally. The present study was undertaken to explore the possibility of expediting the idli batter fermentation process by adding an exogenous source of α-amylase enzyme. 5, 15 and 25 U per 100 g batter of amylase were added to the idli batter which was allowed to ferment. Different parameters were monitored and sensory attributes were also studied and compared with that of the control set. The fermentation time was reduced from a conventional 14 h to 8 h and the sensory attributes of the final product were also successfully maintained.     

The rate of formation of intermetallic layers between aluminum and steel below 660°C

The rate of formation of intermetallic compounds between aluminum and three ferritic steels, one austenitic steel, and Inconel has been determined by an electrolytic method. The steel was held at zero potential with respect to aluminum in a NaCl-AlCl₃ melt, and the current measured. Comparison of measured thicknesses of intermetallic layers with those calculated from the integrated current gives an average deposition efficiency of 95 pct. For the Type 304 austenitic steel thickness (min), andk is given by logk= −6400/T(⁰K) +4.469. The ferritic steels show a linear rate of growth of Al₅Fe₂, with an initial higher rate such that extrapolation of the linear curve back to zero time gives an intercept of 16±7 μm. The rate constants (mm min⁻¹) may be represented by log (rate)=α/T+β, and the values of α and β are respectively −2650 and−0.788 for a plain carbon steel,−6580 and + 3.469 for a 1.3 pct Cr, 0.4 pct Mo steel, and−5950 and +2.466 for a 2.2 pct Cr, 0.9 pct Mo steel. The more highly alloyed steels are thus attacked, more slowly. Results for Inconel could not be fitted to any simple equation. With the ferritic steels growth is by aluminum diffusing inwards; with Inconel it is by nickel diffusing outward.     

Austenite stabilization in stainless steel by hydrogen

It has been found that stabilization of austenite by hydrogen is governed not by its amount but by the manner of its introduction into the austenite just prior to transformation into martensite. In this case stabilization is to be understood as a decreasing tendency to transformation into martensite. The experimental results obtained using an appropriate material (steel No. 1.4576) show that cathodic impregnation brings about a stabilization of austenite as defined above.     

The influence of radioactive n-dibutyl sulphide on the corrosion and polarization of steel and its electrocapillary behaviour in in sulphuric acid

The corrosion and polarization of steel have been investigated in 1N sulphuric acid, containing n-dibutyl sulphide labelled with radioactive sulphur atom. In addition, the electrocapillary behaviour of the radioactive substance on a mercury surface in the acid has been tested. Similar experiments employing non-radioactive dibutyl sulphide (d.b.s.) and hydrogen peroxide have been carried out.The inhibition of corrosion of steel in IN sulphuric acid by d.b.s. is significantly reduced and under some conditions corrosion is accelerated by the radioactive form. The polarization and the electrocapillary behaviour of radioactive d.b.s. solutions are clearly different from that of the non-radioactive compound. There is some similarity in the effects produced by radioactive d.b.s. and by a combination of non-radioactive d.b.s. and hydrogen peroxide, in respect of corrosion inhibition and electrocapillary behaviour. It is concluded that the effects produced by radioactive d.b.s. can be attributed mainly to the hydrogen peroxide produced by radiolysis, though the radioactivity can also affect the electrical characteristics at the metal-solution interface.     

Silicon-germanium base heterojunction bipolar transistors bymolecular beam epitaxy

The devices were fabricated using molecular-beam epitaxy (MBE), low-temperature processing, and germanium concentrations of 0, 6%, and 12%. The transistors demonstrate current gain, and show the expected increase in collector current as a result of reduced bandgap due to Ge incorporation in the base. For a 1000-Å base device containing 12% Ge, a six-times increase in collector current was measured at room temperature, while a 1000-times increase was observed to 90 K. The temperature dependence of the collector current of the Si_0.88Ge_0.12 base transistor is consistent with a bandgap shrinkage in the base of 50 meV. For the homojunction transistors, base widths as thin as 800 Å were grown, corresponding to a neutral base width of no more than 400 Å     

Thermal noise in the linear graded channel junction FET

The limiting noise mechanism in field effect transistors is thermal noise of the conducting channel. An analysis of the thermal noise in a linearly tapered inhomogeneous channel FET is presented leading to a solution for the open circuit noise voltage and the short circuit noise current. Improvement in the open circuit noise voltage for the inhomogeneous FET is shown directly from a comparison with the solution for a homogeneous channel FET.