Browsing by Author "Joshi, Nandan"

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    Actor systems platform design and implementation of the actor paradigm in a distributed object-oriented environment
    Joshi, Nandan (Virginia Tech, 1993-08-05)
    This project was undertaken as part of an effort to explore the design of object -oriented systems that are distributed, concurrent, real-time and/or embedded in nature. This work seeks to integrate the concurrency features of the actor model in a distributed, object oriented environment, ESP. The integrated system, called the Actor Systems Platform (ASP), provides a platform for designing concurrent, distributed applications. The actor model provides a mechanism for expressing the inherent concurrency in an application. The concurrency in the application can be exploited by the distributed features available in ESP. The actor abstraction in ASP is provided by a application-level class hierarchy in ESP. The message passing semantics of the actor model are implemented by using special operator overloading in C++. Cboxes are implemented to provide a synchronization mechanism and a means of returning replies. In a concurrent system, simultaneous execution of an object's methods can cause its state to be inconsistent. This is prevented by providing a method locking mechanism using behavior sets. While integrating the concurrency features of the actor model in an object-oriented environment, differences were encountered in determining the invocation semantics of the actor model and those of inherited methods. The problem is investigated and a taxonomy of solutions is presented.
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    Mobility analysis of variable geometry trusses
    Joshi, Nandan (Virginia Tech, 1988-02-05)
    Parallel manipulators are being thought of as a solution to many problems involving control and manipulation. They offer significant advantages over serial manipulators in terms of increased strength and rigidity. Variable geometry trusses (VGTs) are a special class of parallel trusses. Literature on VGTs has covered many interesting problems, yet there has been no conscious effort to formulate a definition for a VGT. The major emphasis of this thesis is developing a set of precise kinematic rules for defining and analyzing VGTs. Traditional mobility criteria, when applied to parallel geometries, predict results which are often confusing and sometimes inaccurate. Based on the set of rules developed, mobility equations are derived for planar and spatial VGTs. The equations are tested on a sufficiently large number of VGT configurations to convince the author about the validity of the set of rules and the equations derived. Using the mobility equations, different candidate geometries can be analyzed and compared. In addition, the equations can be used in the type and number synthesis of VGTs.