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16 Jan 2012

Volume 100, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 100, 033109 (2012); http://dx.doi.org/10.1063/1.3664636 (3 pages)

Sang H. Yun, Hyung-Seok Lee, Young Ha Kwon, Mats Göthelid, Sang Mo Koo, Lars Wågberg, Ulf O. Karlsson, and Jan Linnros
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Investigation of atypical molten pool dynamics in tungsten carbide-cobalt during laser deposition using in-situ thermal imaging

Yuhong Xiong, William H. Hofmeister, John E. Smugeresky, Jean-Pierre Delplanque, and Julie M. Schoenung

Appl. Phys. Lett. 100, 034101 (2012); http://dx.doi.org/10.1063/1.3676420 (4 pages) | Cited 1 time

Online Publication Date: 18 January 2012

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An atypical “swirling” phenomenon observed during the laser deposition of tungsten carbide-cobalt cermets by laser engineered net shaping (LENS®) was studied using in-situ high-speed thermal imaging. To provide fundamental insight into this phenomenon, the thermal behavior of pure cobalt during LENS was also investigated for comparison. Several factors were considered as the possible source of the observed differences. Of those, phase difference, material emissivity, momentum transfer, and free surface disruption from the powder jets, and, to a lesser extent, Marangoni convection were identified as the relevant mechanisms.
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66.25.+g Thermal conduction in nonmetallic liquids
81.05.Mh Cermets, ceramic and refractory composites

Modeling the quantum efficiency of controlled porosity dispenser photocathodes

Z. Pan, K. Jensen, and P. O’Shea

Appl. Phys. Lett. 100, 034102 (2012); http://dx.doi.org/10.1063/1.3678035 (3 pages)

Online Publication Date: 20 January 2012

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A theoretical model of diffusion, evaporation, and rejuvenation of cesium on the surface of a controlled porosity dispenser photocathode is developed. The model applies a novel hexagonal meshgrid for increased numerical accuracy. For activation temperatures within the range of 400 K–1000 K, simulation found differences of less than 5% between the quantum efficiency (QE) maximum and minimum over ideal homogenous surfaces. Simulations suggest more variation for real cases to include real surface non uniformity. Changes in the QE map across the surface suggest that the emittance can change depending on temperature. Extensions to the model as well as connections to experiment are discussed.
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85.60.Ha Photomultipliers; phototubes and photocathodes
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