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15 Aug 2002

Volume 92, Issue 4, pp. 1727-2219

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The convergence condition of the successive approximation process in Compton scattering tomography

Jiajun Wang, Xianwu Huang, and Xingrong Zhong

J. Appl. Phys. 92, 2149 (2002); http://dx.doi.org/10.1063/1.1494112 (4 pages)

Online Publication Date: 30 July 2002

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Compton scattering can be used to determine the electron densities of tissues for medical applications and those of materials for industrial applications. Much work has been devoted to solving the reconstruction problem. Hussein proposed a successive approximation process (SAP) for the reconstruction of the density image from the Compton scattered energy spectral data [IEEE Trans. Nucl. Sci., 42, 2155 (1995)]. This algorithm is adapted directly from the neutron scattering tomography reconstruction where a convergence condition for such an algorithm was presented [Hussein and Meneley, Int. J. Multiphase Flow, 12, 1 (1986)]. However, we found that this condition is not correct in general cases and we cannot obtain such a simple form of convergence condition in terms of the maximum length(in unit of mean-free path) a neutron or a photon travels in any pixel in the test section. A detailed discussion of the convergence problem of SAP will be presented in this paper. © 2002 American Institute of Physics.
Show PACS
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
07.05.Pj Image processing
78.70.Ck X-ray scattering

Subpicosecond laser ablation of dental enamel

A. V. Rode, E. G. Gamaly, B. Luther-Davies, B. T. Taylor, J. Dawes, A. Chan, R. M. Lowe, and P. Hannaford

J. Appl. Phys. 92, 2153 (2002); http://dx.doi.org/10.1063/1.1495896 (6 pages) | Cited 29 times

Online Publication Date: 30 July 2002

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Laser ablation of dental enamel with subpicosecond laser pulses has been studied over the intensity range of (0.1–1.4)×1014 W/cm2 using 95 and 150 fs pulses at a pulse repetition rate of 1 kHz. The experimentally determined ablation threshold of 2.2±0.1 J/cm2 was in good agreement with theoretical predictions based on an electrostatic ablation model. The ablation rate increased linearly with the laser fluence for up to 15 times the ablation threshold. The absence of collateral damage was observed using optical and scanning electron microscopy. Pulpal temperature measurements showed an increase of about 10 °C during the 200 s course of ablation. However, air cooling at a rate of 5 l/min resulted in the intrapulpal temperature being maintained below the pulpal damage threshhold of 5.5 °C. The material removal rates for subpicosecond precision laser ablation of dental enamel are compared with other techniques. © 2002 American Institute of Physics.
Show PACS
42.62.Be Biological and medical applications
87.63.L- Visual imaging
87.50.-a Effects of electromagnetic and acoustic fields on biological systems
87.64.M- Optical microscopy
87.64.mk Confocal
87.19.Pp Biothermics and thermal processes in biology
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