Maintaining quality lead-free [circuit board inspection]

The change to lead-free solders means that circuit board inspection will become more important than ever. The author investigates differences between lead and lead-free solders.     

Modification of the method of simulation of truncated random variables

A new method for simulation of truncated random variables is described. Several similar methods are considered. It is shown that a substantial reduction in computation time is achieved by utilizing the proposed method.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 12–13, April, 1995.     

Effect of thermal load on heat-transfer coefficient in porous-sublimation cooling

It was shown that, under thermal loads that are sufficiently larger (smaller) than a certain value, the heat transfer coefficient for porous-sublimation cooling increases (decreases) with an increase in the thermal load.Physico-Technical Low Temperatures Institute, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Inzlieneron-Fizicheskii Zhurnal, Vol. 62, No. 6, pp. 783–785, June, 1992.     

CONSTRUCTION OF ADMISSIBLE OPERATION CONDITION DOMAIN FOR WELL-STIRRED REACTORS DURING THEIR DESIGN AND CONTROL STAGES

The work examines the problem of constructing an admissible operation condition domain for a well-stirred reactor which would satisfy restrictions in conversion, selectivity, heat removal and stability. The domain is very important and must be known during the reactor design and control stages because it yields visual information for analyzing the reactor operations and makes it possible to find the variation intervals of decision variables, necessary to calculate and optimize the reactor. Being known, the admissible operation condition domain makes it possible to estimate the limiting restrictions and to choose the necessary reserves. The domain has completely been studied analytically for chemical processes with arbitrary kinetics.     

Determining the reliability of concrete dams through diagnosis of their bedrock

Power Technology and Engineering -     

Volume effects and associations in liquid alloys

The regular associated solution model for binary systems has been modified by incorporating the size of the complex as an explicit variable. The thermodynamic properties of the liquid alloy and the interactions between theA _μB type of complex and the unassociated atoms in anA-B binary have been evaluated as a function of relative size of the complex using the activity coefficients at infinite dilution and activity data at one other composition in the binary. The computational procedure adopted for determining the concentration of clusters and interaction energies in the associated liquid is similar to that proposed by Lele and Rao. The analysis has been applied to the thermodynamic mixing functions of liquid Al-Ca alloys believed to contain Al₂Ca associates. It is found that the size of the cluster significantly affects the interaction energies between the complex and the unassociated atoms, while the equilibrium constant and enthalpy change for the association reaction exhibit only minor variation, when the equations are fitted to experimental data. The interaction energy between unassociated free atoms remains virtually unaltered as the size of the complex is varied between extreme values. Accurate data on free energy, enthalpy, and volume of mixing at the same temperature on alloy systems with compound forming tendency would permit a rigorous test of the proposed model.     

Intelligent assistance for software development and maintenance

An environment is described, called Professor Marvel, that provides early error checking and answers questions about the program under development. The environment has a certain understanding of the systems being developed and how to use tools to produce software. It aids individual programmers and helps coordinate programming teams. The key components of Marvel are a database that stores data represented as objects, as in object-oriented languages, and a model of the development process that imposes a structure on programming activities. Marvel's support of insight and of opportunistic processing is discussed at length, as is the handling of side effects. A sample session is described