Making On-Demand Routing Efficient with Route-Request Aggregation

In theory, on-demand routing is very attractive for mobile ad hoc networks (MANET), because it induces signaling only for those destinations for which there is data traffic. However, in practice, the signaling overhead of existing on-demand routing protocols becomes excessive as the rate of topology changes increases due to mobility or other causes. We introduce the first on-demand routing approach that eliminates the main limitation of on-demand routing by aggregating route requests (RREQ) for the same destinations. The approach can be applied to any existing on-demand routing protocol, and we introduce the Ad-hoc Demand-Aggregated Routing with Adaptation (ADARA) as an example of how RREQ aggregation can be used. ADARA is compared to AODV and OLSR using discrete-event simulations, and the results show that aggregating RREQs can make on-demand routing more efficient than existing proactive or on-demand routing protocols

NASA-UVA Light Aerospace Alloy and Structures Technology Program (LA2ST)

The NASA-UVA Light Aerospace Alloy and Structures Technology (LA2ST) Program was initiated in 1986 and continues with a high level of activity. Here, we report on progress achieved between July I and December 31, 1996. The objective of the LA2ST Program is to conduct interdisciplinary graduate student research on the performance of next generation, light-weight aerospace alloys, composites and thermal gradient structures in collaboration with NASA-Langley researchers. Specific technical objectives are presented for each research project. We generally aim to produce relevant data and basic understanding of material mechanical response, environmental/corrosion behavior, and microstructure; new monolithic and composite alloys; advanced processing methods; new solid and fluid mechanics analyses; measurement and modeling advances; and a pool of educated graduate students for aerospace technologies. The accomplishments presented in this report are summarized as follows. Three research areas are being actively investigated, including: (1) Mechanical and Environmental Degradation Mechanisms in Advanced Light Metals, (2) Aerospace Materials Science, and (3) Mechanics of Materials for Light Aerospace Structures

The interlamellar atomic habit plane in Cu-6% Be pearlite

This investigation has sought to gain a better understanding of interphase boundaries in lamellar solid-solid phase transformations. Transmission electron microscopy has been used to characterize the f.c.c./ordered b.c.c. interface in the eutectoid Cu-6% Be binary. The atomic habit plane is established to be (111)f.c.c.//(110)b.c.c. with [110]f.c.c.//[111]b.c.c. Direction steps similar to those described by Hackney and Shiflet in ferrous pearlites were the only interfacial defect observed. Using point group intersection theory and our experimental results, it is shown that although the atomic habit plane is not a symmetry-dictated energy extremum, it is a minimum in energy space. © 1988 Taylor & Francis Group, LLC

Application of the Kaufman approach to the calculation of intra-rare earth phase diagrams

The Kaufman approach is combined with values of Δ°H and Δ°S for transformations in pure rare earths to construct phase diagrams for some simple binary systems. Good agreement is obtained for the Dy-Er, Dy-Ho, Tb-Ho and Tb-Er peritectics and for the Ho-Er isomorphous phase diagram. Only limited agreement is attained for the Nd-Pr and Gd-Y double isomorphous systems. The phase diagrams for Sc and the elements Y, Nd, and Gd were least satisfactory. Where agreement is poor, the effects of impurities and other uncertainties are discussed. © 1979