27,398 research outputs found
Maximizing the Probability of Delivery of Multipoint Relay Broadcast Protocol in Wireless Ad Hoc Networks with a Realistic Physical Layer
It is now commonly accepted that the unit disk graph used to model the
physical layer in wireless networks does not reflect real radio transmissions,
and that the lognormal shadowing model better suits to experimental
simulations. Previous work on realistic scenarios focused on unicast, while
broadcast requirements are fundamentally different and cannot be derived from
unicast case. Therefore, broadcast protocols must be adapted in order to still
be efficient under realistic assumptions. In this paper, we study the
well-known multipoint relay protocol (MPR). In the latter, each node has to
choose a set of neighbors to act as relays in order to cover the whole 2-hop
neighborhood. We give experimental results showing that the original method
provided to select the set of relays does not give good results with the
realistic model. We also provide three new heuristics in replacement and their
performances which demonstrate that they better suit to the considered model.
The first one maximizes the probability of correct reception between the node
and the considered relays multiplied by their coverage in the 2-hop
neighborhood. The second one replaces the coverage by the average of the
probabilities of correct reception between the considered neighbor and the
2-hop neighbors it covers. Finally, the third heuristic keeps the same concept
as the second one, but tries to maximize the coverage level of the 2-hop
neighborhood: 2-hop neighbors are still being considered as uncovered while
their coverage level is not higher than a given coverage threshold, many
neighbors may thus be selected to cover the same 2-hop neighbors
High-Fidelity Archeointensity Results for the Late Neolithic Period From Central China
Archeomagnetism focuses on exploring high-resolution variations of the geomagnetic field over hundreds to thousands of years. In this study, we carried out a comprehensive study of chronology, absolute and relative paleointensity on a late Neolithic site in central China. Ages of the samples are constrained to be ~3,500–3,000 BCE, a period when available paleointensity data are sparse. We present a total of 64 high-fidelity absolute paleointensities, demonstrating the field varied quickly from ~55 to ~90 ZAm2 between ~3,500–3,000 BCE. Our results record a new archeomagnetic jerk around 3,300 BCE, which is probably non-dipolar origin. The new results provide robust constraints on global geomagnetic models. We calculated a revised Chinese archeointensity reference curve for future application. The variations of absolute and relative paleointensity versus depth show good consistency, reinforcing the reliability of our results. This new attempt of combining absolute and relative paleointenstiy provides a useful tool for future archeomagnetic research
Morphology and Orientation Selection of Non-Metallic Inclusions in Electrified Molten Metal
The effect of electric current on morphology and orientation selection of non-metallic inclusions in molten metal has been investigated using theoretical modelling and numerical calculation. Two geometric factors, namely the circularity (fc) and alignment ratio (fe) were introduced to describe the inclusions shape and configuration. Electric current free energy was calculated and the values were used to determine the thermodynamic preference between different microstructures. Electric current promotes the development of inclusion along the current direction by either expatiating directional growth or enhancing directional agglomeration. Reconfiguration of the inclusions to reduce the system electric resistance drives the phenomena. The morphology and orientation selection follows the routine to reduce electric free energy. The numerical results are in agreement with our experimental observations
Process and machine system development for the forming of miniature/micro sheet metal products
This paper reports on the current development of the process for the forming of thin sheet-metal micro-parts (t < 50µm) and the corresponding machine system which is part of the research and technological development of an EU funded integrated project - MASMICRO ("Integration of Manufacturing Systems for the Mass-Manufacture of Miniature/Micro-Products" (/www.masmicro.net/). The process development started with qualification of the fundamentals related to the forming of thin sheet-metals in industrial environment, for which a testing machine and several sets of the testing tools were developed. The process was further optimised, followed by new tool designs. Based on the experience gained during the process development, a new forming press which is suitable for industrial, mass-customised production, has been designed
Path Integrals and Alternative Effective Dynamics in Loop Quantum Cosmology
The alternative dynamics of loop quantum cosmology is examined by the path
integral formulation. We consider the spatially flat FRW models with a massless
scalar field, where the alternative quantization inherit more features from
full loop quantum gravity. The path integrals can be formulated in both
timeless and deparameterized frameworks. It turns out that the effective
Hamiltonians derived from the two different viewpoints are equivalent to each
other. Moreover, the first-order modified Friedmann equations are derived and
predict quantum bounces for contracting universe, which coincide with those
obtained in canonical theory.Comment: 8 pages. arXiv admin note: substantial text overlap with
arXiv:1102.475
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