National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Hiding expressed using relation algebra with multi-relations-oblique lifting and lowering for unbalanced systems

Abstract: The analysis of existing software architectures may be supported by a relational approach. The approach is based on relational algebra with multi-relations extended with a theory about "lifting". Lifting transforms a relation at a certain level of the decomposition structure of a system (e.g. the module level) to a higher level (e.g. the subsystem level). The application of lifting has been reported for various industrial contexts for balanced systems (i.e. systems where the decomposition structure is a balanced tree). This paper reports upon a more liberal kind of lifting, termed "oblique lifting", which has the important advantage that it can also be used for unbalanced systems. Lowering, the opposite of lifting, can be liberalized in a similar fashion. The use of oblique lowering is illustrated by means of a typical example from the field of software architecture verification. The leading example of this paper uses the relational approach as a formal basis for a software architecture browser visualizing the module interconnection architecture of a software system. Oblique lifting is applied to hiding the decomposition structure of a module in a module interconnection diagram by choosing an appropriate mapping. After the hiding, various kinds of weights (or multiplicities) may be associated with the interconnections in the resulting diagram. Four definitions of weights are described, including the formalization of their related operations, with each weight having its own merits during architectural analysis.

Nitride-bonded silicon nitride from slip-cast Si + Si3N4 compacts

Abstract: The dispersability of Si and Si3N4 powders in aqueous media was monitored by particle-size distribution, sedimentation behavior, viscosity/rheological studies, and electrokinetic behavior [zeta potential (ZP) analysis] as a function of pH of their slips. The pH values of 4 and 8 for Si and 10 for Si3N4 resulted in optimum dispersion, characterized by minimum in sedimentation height, minimum in viscosity, and maximum in ZP. The optimum slips of Si + Si3N4 mixtures conditioned in the pH range 8 to 10 were slip cast to obtain green compacts having a density in the range of 59% to 66% theoretical value. When nitrided, these compacts yielded nitride-bonded Si3N4 products having a density of 2.06 to 2.28 g cm−3, Si3N4 bonding phase of 20–60%, and 3-point flexural strength values in the range of 50 to 150 MPa. The microstructure consisted of very fine particles as well as fibrous or whiskerlike α–Si3N4 binding phase enveloping the matrix Si3N4, in total consisting of 90% α–Si3N4 and the rest being β–Si3N4 phase.