Attenuation of leaky modes and filtering techniques in graded index multimode fibres

This work is an investigation of leaky ray (mode) attenuation in graded multimode fibres. In contrast to slab or rectangular dielectric waveguides, cylindrical fibres possess leaky modes which greatly modify their propagation properties. The power carried by such modes eventually diminishes to zero, thus adding no useful contribution to the signal transmission over fibre channels. Suitable filtering techniques are therefore proposed. [Continues.

Generation of J0 Bessel Beams with controlled spatial coherence features

An alternative method to generate J0 Bessel beams with controlled spatial partial coherence properties is introduced. Far field diffraction from a discrete number of source points on an annular region is calculated. The average for different diffracted fields produced at several rotation angles is numerically calculated and experimentally detected. Theoretical and experimental results show that for this particular case, J0 Bessel beam is a limit when the number of points tends towards infinity and the associated complex degree of coherence is also a function of the number of points.Comment: 6 pages, 5 figure

Effects of circumferential pick spacing on boom type roadheader cutting head performance

Effects of equal and unequal circumferential pick spacing on the performance of boom type roadheaders having cylindrical cutting heads are investigated. For this purpose, two experimental cutting heads with equal and unequal circumferential spacing are designed and manufactured. The cutting head with unequal circumferential spacing is specifically designed to prevent tool-holder overlap at the nose section. Manufacturing difficulties associated with equal circumferential pick spacing due to tool-holder overlap are discussed with solid modeling and practical applications. The heads are tested at Park Cayirhan Coal Mine in Turkey and their cutting performances are analysed. Although better cutting performance for equal circumferential spacing are predicted by force-balance analysis, in situ measurements of instantaneous (net) traversing speed and cutting rate, pick consumption rate and machine vibration show that no significant difference exists between the performances of the two cutting heads. (C) 2005 Elsevier Ltd. All rights reserved

Effects of circumferential pick spacing on boom type roadheader cutting head performance

Effects of equal and unequal circumferential pick spacing on the performance of boom type roadheaders having cylindrical cutting heads are investigated. For this purpose, two experimental cutting heads with equal and unequal circumferential spacing are designed and manufactured. The cutting head with unequal circumferential spacing is specifically designed to prevent tool-holder overlap at the nose section. Manufacturing difficulties associated with equal circumferential pick spacing due to tool-holder overlap are discussed with solid modeling and practical applications. The heads are tested at Park Cayirhan Coal Mine in Turkey and their cutting performances are analysed. Although better cutting performance for equal circumferential spacing are predicted by force-balance analysis, in situ measurements of instantaneous (net) traversing speed and cutting rate, pick consumption rate and machine vibration show that no significant difference exists between the performances of the two cutting heads