A 2-D random-walk mobility model for location-management studies in wireless networks

In this work, a novel two-dimensional (2-D) random-walk mobility model is proposed, which can be used for studying and analyzing the location-area crossing rate and dwell time of mobile users in wireless networks. The development and application of the model under two cell structures, namely the square and hexagon cells, have been detailed. The analytical results obtained for location-update rates and dwell times have been validated using simulated and published results. The highlights of the model are its simplicity, minimal assumptions, and adaptability to conduct both "location-crossing rate" and "dwell-time" studies using the same model with slight modifications for either the square or hexagon cells. Using symmetry of mobile-user movement, a reduced number of computational states was achieved. A novel wrap-around feature of the model facilitates reduced assumptions on user mobility, which has also resulted in considerably reduced mathematical computation complexity. A regular Markov chain model was used for computing the average location-area crossing rate. A slightly modified model with absorbing states was used to derive the dwell time. This is the first model of its kind that can be used for studying area-crossing rates. To further emphasize the flexibility of the model, we have extended the model to study an overlapped location-area strategy. The study and analysis of overlapped locations areas has hitherto been difficult due to the complexity of the models.     

Design and implementation of a semantic query optimizer

The authors describe a scheme to utilize semantic knowledge in optimizing a user-specified query. The semantics is represented as function-free clauses in predicate logic. The scheme uses a graph-theoretic approach to identify redundant joins and restrictions present in a given query while adding additional profitable specifications to it. Dynamic and heuristic interaction of three entities-schema, semantics, and query-forms the basis of the algorithm. The implementation architecture of the algorithm and test results on a representative set of data are presented. Issues associated with updating of semantic constraints are addressed, and an algorithm for semantic maintenance is introduced     

Implications of proxy caching for provisioning networks and servers

In this paper, we examine the potential benefits of Web proxy caches in improving the effective capacity of servers and networks. Since networks and servers are typically provisioned based on a high percentile of the load, we focus on the effects of proxy caching on the tail of the load distribution. We find that, unlike their substantial impact on the average load, proxies have a diminished impact on the tail of the load distribution. The exact reduction in the tail and the corresponding capacity savings depend on the nature of the workload and the percentile of the load distribution chosen for provisioning networks and servers-the higher the percentile, the smaller the savings. For workloads considered in this study, compared with over a 50% reduction in the average load, the savings in network and server capacity was only 20%-35% for the 99th percentile of the load distribution. We also find that while proxies can be somewhat useful in smoothing out some of the burstiness in Web workloads; the resulting workload continues, however, to exhibit substantial burstiness and a heavy-tailed nature. We identify one-time requests for large objects to be the limiting factor that diminishes the impact of proxies on the tail of load distribution. We conclude that, while proxies are immensely useful to users due to the reduction in the average response time, they are less effective in improving the capacities of networks and servers.     

Propagating belief functions in AND-trees

We describe a simple method for propagating belief functions in AND-trees. We exploit the properties of AND-trees to make our method simpler than the general method discussed by Shenoy and Shafer, and Dempster and Kong. We illustrate our method for aggregation of evidence in a financial audit. © 1995 John Wiley & Sons, Inc.     

Laminar natural convection heat transfer to a viscoelastic fluid

A theoretical analysis of laminar natural convection heat transfer to a viscoelastic fluid has been done by the approximate integral method. It has bee     

Natural convection effects on heat transfer to power-law fluids flowing under turbulent conditions in vertical pipes

A theoretical analysis of the effect of buoyancy on the heat transfer to non-Newtonian power-law fluids for upward flow in vertical pipes under turbulent conditions has been presented. A criteria for limiting the reduction in heat transfer to less than 5% has been developed for varying pseudoplasticity index. The equation for quantitative evaluation of the natural convection effect on the forced convection has been suggested to be applicable for upward as well as downward flow of the power-law fluids by a change in the sign of the controlling term.