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Discrete sensor placement problems in distribution networks

Hart, William E.; Hart, William E.

We consider the problem of placing sensors in a network to detect and identify the source of any contamination. We consider two variants of this problem: (1) sensor-constrained: we are allowed a fixed number of sensors and want to minimize contamination detection time; and (2) time-constrained: we must detect contamination within a given time limit and want to minimize the number of sensors required. Our main results are as follows. First, we give a necessary and sufficient condition for source identification. Second, we show that the sensor and time constrained versions of the problem are polynomially equivalent. Finally, we show that the sensor-constrained version of the problem is polynomially equivalent to the asymmetric k-center problem and that the time-constrained version of the problem is polynomially equivalent to the dominating set problem.

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Growth and morphology of cadmium chalcogenides : the synthesis of nanorods, tetrapods, and spheres from CdO and Cd(O[2]CCH[3])[2]

Proposed for publication in the Journal of Chemistry and Materials.

Bunge, Scott D.; Boyle, Timothy J.; Rodriguez, Mark A.; Headley, Thomas J.

In this work, we investigated the controlled growth of nanocrystalline CdE (E = S, Se, and Te) via the pyrolysis of CdO and Cd(O2CCH3)2 precursors, at the specific Cd to E mole ratio of 0.67 to 1. The experimental results reveal that while the growth of CdS produces only a spherical morphology, CdSe and CdTe exhibit rod-like and tetrapod-like morphologies of temporally controllable aspect ratios. Over a 7200 s time period, CdS spheres grew from 4 nm (15 s aliquot) to 5 nm, CdSe nanorods grew from dimensions of 10.8 x 3.6 nm (15 s aliquot) to 25.7 x 11.2 nm, and CdTe tetrapods with arms 15 x 3.5 nm (15 s aliquot) grew into a polydisperse mixture of spheres, rods, and tetrapods on the order of 20 to 80 nm. Interestingly, long tracks of self-assembled CdSe nanorods (3.5 x 24 nm) of over one micron in length were observed. The temporal growth for each nanocrystalline material was monitored by UV-VIS spectroscopy, transmission electron spectroscopy, and further characterized by powder X-ray diffraction. This study has elucidated the vastly different morphologies available for CdS, CdSe, and CdTe during the first 7200 s after injection of the desired chalcogenide.

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Results 12126–12150 of 12,511
Results 12126–12150 of 12,511
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