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Spectral Composition (spectral + composition)
Selected AbstractsSpectral composition of electromagnetic fluctuations induced by a lossy layered systemANNALEN DER PHYSIK, Issue 7-8 2003I. Dorofeyev Abstract We calculate the spectral characteristics of fluctuating electromagnetic fields generated by a half-space covered with a film of an arbitrary thickness. Materials of the half-space and the film are described by different complex permittivities. Expressions for spectral power densities of fluctuating fields and all spatial derivatives expressed via Fresnel coefficients for "p" and "s" waves are derived. Various limiting cases for propagating and evanescent waves in cases of different film thickness are considered. Possible contributions to spectral power densities from interface excitations and wave-guide modes are discussed by analyzing the Fresnel factors in the expressions. Using the results for spatial derivatives a closed analytical expression for a multipolar force acting on a small particle near a half-space is found for multipoles of all orders. The case for a dipole interaction follows directly from a general solution. [source] Tonotopic representation of missing fundamental complex sounds in the human auditory cortexEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2003Takako Fujioka Abstract The N1m component of the auditory evoked magnetic field in response to tones and complex sounds was examined in order to clarify whether the tonotopic representation in the human secondary auditory cortex is based on perceived pitch or the physical frequency spectrum of the sound. The investigated stimulus parameters were the fundamental frequencies (F0 = 250, 500 and 1000 Hz), the spectral composition of the higher harmonics of the missing fundamental sounds (2nd to 5th, 6th to 9th and 10th to 13th harmonic) and the frequencies of pure tones corresponding to F0 and to the lowest component of each complex sound. Tonotopic gradients showed that high frequencies were more medially located than low frequencies for the pure tones and for the centre frequency of the complex tones. Furthermore, in the superior,inferior direction, the tonotopic gradients were different between pure tones and complex sounds. The results were interpreted as reflecting different processing in the auditory cortex for pure tones and complex sounds. This hypothesis was supported by the result of evoked responses to complex sounds having longer latencies. A more pronounced tonotopic representation in the right hemisphere gave evidence for right hemispheric dominance in spectral processing. [source] Sleep during the Antarctic winter: preliminary observations on changing the spectral composition of artificial lightJOURNAL OF SLEEP RESEARCH, Issue 3 2008GAVIN FRANCIS Summary Antarctic Base personnel live for 3 months in winter with no natural sunlight. This project compared sleep, by actigraphy, during periods of increased exposure to white light or blue enriched light in 2003. The primary aim was to help define the optimum spectral composition and intensity of artificial environmental light. Nine men and one woman (33 ± 7 years, mean ± SD), wore activity and light monitors continuously from 28.2 to 9.10, and kept sleep diaries. Extra light was provided by light boxes (standard white, 5300 K, or prototype blue enriched, 10 000K, Philips Lighting), which were turned on in bedrooms and in communal/work areas approximately 08.00,18.00 hours. After a no-treatment control period, 28.2,20.3, sequential 4,5 week periods of first white, then blue light, were imposed with a further control period 19.9,9.10. A limited baseline study in 2002 (no interventions) similarly measured light and activity in seven men and one woman (30 ± 7 years). Daily light exposure in winter (lux, mean ± SD) was doubled in 2003 (maximum 1039 ± 281, average 64 ± 21), compared to 2002 (572 ± 276 and 30 ± 11), P < 0.05 and P < 0.01, with no differences between white and blue light. There were no major differences in sleep between light conditions in 2003. A delay in sleep timing was found in midwinter compared to control (2003, bedtime, P < 0.05, sleep start, P < 0.05, sleep end, P < 0.01) and sleep fragmentation increased (P < 0.05). Sleep efficiency was slightly higher during all blue light periods compared to all white periods (P < 0.05). The use of higher intensity light of suitable spectral composition is proposed. [source] Impact of spectral composition on larval haddock, Melanogrammus aeglefinus L., growth and survivalAQUACULTURE RESEARCH, Issue 4 2002Gavin Downing Abstract In a small-scale culture experiment, larval haddock, Melanogrammus aeglefinus L., were raised under various combinations of light quality [blue (470 nm), green (530 nm) or full-spectrum white light] and light intensity [low (0.3,0.4 µmol s,1 m,2) or high (1.7,1.9 µmol s,1 m,2)], and in total darkness (both fed, and starved). Larval growth (0.9% day,1 in standard length; 2.4% day,1 in body area) was not significantly different between any combination of coloured light. At the time of total mortality in the starved treatment, survival was significantly reduced under low intensity, full-spectrum white light (13%) vs. all other coloured light treatments (68%). Larvae raised under both continuous dark treatments (fed and starved) exhibited morphological changes associated with irreversible starvation (point-of-no-return). Lack of a pronounced effect of light quality on larval haddock growth probably results from a combination of plasticity in early larval vision, and enhanced encounter rates between larvae and prey at the relatively high prey densities used in aquaculture. [source] Pre-receptoral spectral absorption, healthy ageing and pre-clinical indications of retinal diseaseACTA OPHTHALMOLOGICA, Issue 2009E KONSTANTAKOPOULOU Purpose The aim of this study was to investigate how chromatic sensitivity changes as a function of age and to establish the extent to which such changes can be attributed to pre-receptoral spectral absorption of short wavelength light and/or changes in retinal mechanisms caused by ageing. Methods The absorption of blue light by the macular pigment (MP) and the crystalline lens and the subjects' sensitivity to rapid flicker were measured using the Macula Assessment Profile (MAP) test. Red-green (RG) and yellow blue (YB) chromatic detection thresholds were measured at the fovea for young and older subjects using the Colour Assessment and Diagnosis (CAD) test at 2.6, 26 and 65 cd/m2. The variables of interest included the spectral absorption of the lens, the optical density of the MP, subject's age and retinal illuminance. Results The absorption of blue light by the lens increased with age. Absorption of blue light by pre-receptoral filters did not affect RG chromatic sensitivity at any of the light levels investigated but had an effect on YB thresholds. The considerably higher colour vision thresholds of some subjects and the subsequent worsening of their chromatic sensitivity at the lower light level may reflect changes in the retina brought about by accelerated aging effects. Conclusion The effect of pre-receptoral absorption of blue light on chromatic sensitivity is small. Ageing affects the amount and spectral composition of the light reaching the photoreceptors and the processing of retinal signals. As a result, flicker sensitivity declines and colour vision deteriorates. Such effects arise mostly from changes in the retina. The MAP and CAD tests help us to detect the effects of accelerated ageing and retinal disease. [source] | ||||||||||