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At least 1,549 records · Page 86Linked to original sources
PubMed1996

A chromatic-cancellation property of human pupillary responses.

The pupil exhibits a response property somewhat analogous to perceptual red-green cancellation. Across a limited range of flash intensities near threshold, pupillary constrictions evoked by red flashes can be reduced, if not nulled, by the simultaneous addition of a green flash. The percentage of trials on which a stimulus-evoked response can be correctly discriminated from noise also falls to chance level as a green flash is added to the red flash. In terms of the quanta absorbed by L and M cones, the cancellation can be modelled as a function of magnitude of 0.65*L-M.

Algorithms↗
PubMed1996

Chromatic content of spectral lights.

Using three novel formats, we compare four estimates of the spectral sensitivity of the opponent stage channels: a Linear Model, Jameson and Hurvich's [Journal of the Optical Society of America, 45, 546-552 (1955)] hue cancellation sensitivities, Gordon and Abramov's [Optical Society of America Technical Digest Series, 15, 12-15 (1987)] hue scaling, and hue matching. The three formats are: the spectrum locus in the opponent equiluminant plane, null lines in the CIE XYZ chart and response functions for unique hues. All sensitivities show departures from the Linear Model and from each other. Relative to the model, common features of all estimates are that violets are compressed; long-wavelength reds are amplified; the redness component of violet lights is greatly attenuated; and saturation of violet stimuli is underestimated.

Color Perception↗
PubMed1982

Baseline and mitomycin-C-induced sister chromatic exchanges ina melanoma and a colon tumor cell line.

Baseline and mitomycin C (MMC)-induced sister chromatid exchanges (SCEs) in two human tumor cell lines (a colon tumor and a melanoma) and in a normal fibroblast cell line were analyzed and compared. The tumor cells showed numerical and structural chromosomal abnormalities. Their baseline SCE rate was slightly, but not significantly, higher than that of the control. Each tumor cell line showed a dose-dependent increase in SCE frequency above the spontaneous level in its own specific manner. The response in the malanoma cell was consistently below that of the control, but only the response to the highest dose of MMC (10(-9) M) was significantly lower than that of the control. The response of the colon tumor cells varied with respect to that of the control. Thus, it appears that karyotypic instability in tumor cells is not necessarily associated with elevated baseline or induced SCE/chromosome rates. In addition, within each cell line dose group, the SCE frequency was proportional to the number of chromosomes. thus, the SCE/chromosome is a better expression of genetic damage than SCE/metaphase in analyses involving heteroploid cells.

Antibiotics, Antineoplastic↗
PubMed1992

A comparison of methods of measuring chromatic activity in the integument of a teleost.

1. Pallor induced by noradrenalin (5 x 10(-7) mol/kg) injection of dark Pseudopleuronectes americanus was measured as increase in skin reflectance and the degree of melanosome aggregation determined. 2. Mean skin reflectance increased approximately 30% on the Munsell neutral value scale. 3. At maximal mean reflectance, melanosomes were fully aggregated in most epidermal melanophores, but displayed more variable aggregation in dermal melanophores. 4. Individual reflectance estimates did not provide consistent indications of melanosome aggregation at maximum pallor. 5. The relative merits of reflectance and cellular methods of estimating melanophore activity are discussed with particular reference to this species.

Animals↗
PubMed1986

Control of chromatophore movements in dermal chromatic units of blue damselfish--II. The motile iridophore.

The mechanism regulating the movements of the unique motile iridophores of the blue damselfish, Chyrsiptera cyanea, was studied. The reaction in which the cells become reflective to light rays of longer wavelength, i.e. from the near u.v. region to the green region, was designated as the "coloring response", while the reverse process was labeled the "clearing response". Both nervous stimuli and adrenergic agonists gave rise to the coloring response, which could be antagonized by alpha adrenolytic agents. The clearing response was accelerated by adenosine and inhibited by theophylline. None of the hormonal substances tested had any effect on the motile response of the cells. It was concluded that the motile iridophores are solely under the control of the sympathetic adrenergic system, and that the co-transmitter, adenosine, may function to antagonize quickly the true transmitter-induced colored state of the cells.

Adenosine↗
PubMed2006

Chromatic photoacclimation, photosynthetic electron transport and oxygen evolution in the chlorophyll d-containing oxyphotobacterium Acaryochloris marina.

Changes in photosynthetic pigment ratios showed that the Chlorophyll d-dominated oxyphotobacterium Acaryochloris marina was able to photoacclimate to different light regimes. Chl d per cell were higher in cultures grown under low irradiance and red or green light compared to those found when grown under high white light, but phycocyanin/Chl d and carotenoid/Chl d indices under the corresponding conditions were lower. Chl a, considered an accessory pigment in this organism, decreased respective to Chl d in low irradiance and low intensity non-white light sources. Blue diode PAM (Pulse Amplitude Modulation) fluorometry was able to be used to measure photosynthesis in Acaryochloris. Light response curves for Acaryochloris were created using both PAM and O(2) electrode. A linear relationship was found between electron transport rate (ETR), measured using a PAM fluorometer, and oxygen evolution (net and gross photosynthesis). Gross photosynthesis and ETR were directly proportional to one another. The optimum light for white light (quartz halogen) was about 206+/-51 micromol m(-2) s(-1) (PAR) (Photosynthetically Active Radiation), whereas for red light (red diodes) the optimum light was lower (109+/-27 micromol m(-2) s(-1) (PAR)). The maximum mean gross photosynthetic rate of Acaryochloris was 73+/-7 micromol mg Chl d(-1) h(-1). The gross photosynthesis/respiration ratio (P(g)/R) of Acaryochloris under optimum conditions was about 4.02+/-1.69. The implications of our findings will be discussed in relation to how photosynthesis is regulated in Acaryochloris.

Chlorophyll↗
PubMed2006

Formation of metal agglomerates during carbonisation of chromated copper arsenate (CCA) treated wood waste: Comparison between a lab scale and an industrial plant.

This paper compares the results obtained by scanning electron microscopy coupled to X-ray analysis (SEM-EDXA) of the solid product after carbonisation of treated wood waste in a lab scale and in an industrial installation. These setups (lab scale and industrial) are characterized by different operating conditions of the carbonisation process. Moreover, the wood waste input to the processes differs significantly. From this study, it is clear that some similarities but also some differences exist between the lab scale study and the study with the industrial Chartherm plant. In both reactors, a metal (and mineral) agglomeration process takes place, even in the case of untreated wood. The agglomerates initially present in the wood input may serve as a seed for the metal agglomeration process during "chartherisation". The industrial setup leads to a broader range of agglomerates' size (0.1-50 microm) and composition (all possible combinations of Cu, Cr, As and wood minerals). Some agglomerates contain the three metals but the major part is a combination of wood minerals and one or two of the three preservative metals, while all agglomerates analysed in the lab scale product contain the three metals. The separate influence of wood input characteristics and process conditions cannot be derived from these experiments, but the observations suggest that the higher the CCA retention in the wood input is, the easier is the metal agglomeration process during chartherisation of CCA treated wood waste. From the analyses performed in this study it seems that copper behaves differently in the sense that it agglomerates easily, but the resulting particles are small (<1 microm).

Arsenates↗
PubMedDate not supplied

A neuromorphic model for achromatic and chromatic surface representation of natural images.

This study develops a neuromorphic model of human lightness perception that is inspired by how the mammalian visual system is designed for this function. It is known that biological visual representations can adapt to a billion-fold change in luminance. How such a system determines absolute lightness under varying illumination conditions to generate a consistent interpretation of surface lightness remains an unsolved problem. Such a process, called 'anchoring' of lightness, has properties including articulation, insulation, configuration, and area effects. The model quantitatively simulates such psychophysical lightness data, as well as other data such as discounting the illuminant, and lightness constancy and contrast effects. The model retina embodies gain control at retinal photoreceptors, and spatial contrast adaptation at the negative feedback circuit between mechanisms that model the inner segment of photoreceptors and interacting horizontal cells. The model can thereby adjust its sensitivity to input intensities ranging from dim moonlight to dazzling sunlight. A new anchoring mechanism, called the Blurred-Highest-Luminance-As-White rule, helps simulate how surface lightness becomes sensitive to the spatial scale of objects in a scene. The model is also able to process natural color images under variable lighting conditions, and is compared with the popular RETINEX model.

Adaptation, Ocular↗
PubMedDate not supplied

Correlation of blue chromatic macular sensitivity with optic disc change in early glaucoma patients.

PURPOSE: To investigate the relationship between morphological changes of the optic nerve head (ONH) and macular sensitivity determined with blue on yellow (B on Y) and white on white (W on W) perimetry in normal subjects and patients with glaucoma. METHODS: One randomly chosen eye was evaluated in each of 28 healthy subjects, 23 patients with ocular hypertension (OH), and 23 patients with early primary open-angle glaucoma (POAG). The mean macular sensitivity determined with B on Y and W on W perimetry was obtained by a macular program using a modified Humphrey field analyzer. The Heidelberg retina tomograph with software version 2.01 was used to evaluate the temporal topographic measurements of ONH. RESULTS: There was no significant difference in temporal ONH parameters among the three clinical groups. The mean macular sensitivity of B on Y and W on W perimetry in early POAG patients was significantly lower than that in healthy subjects and in patients with OH. The mean macular sensitivity of W on W perimetry showed no significant correlation with temporal ONH parameters in any clinical groups. In patients with early POAG, the mean macular sensitivity of B on Y perimetry was significantly related to cup area and volume, cup/disc area ratio, and rim volume in the temporal sector of the ONH. CONCLUSION: The measurement of the mean macular sensitivity of B on Y perimetry might make it possible to detect functional damage prior to morphological changes in the ONH due to elevated intraocular pressure in glaucoma.

Color Vision Defects↗
PubMed2001

Effects of chromated copper arsenate (CCA) wood preservative on early fouling community formation.

The effects of the anti-marine-borer timber preservative CCA (a pressure impregnated solution of copper, chromium and arsenic compounds) on early fouling community formation were investigated during a number of field trials. The formation of a biofilm on the surface of CCA-treated and untreated timber panels of Scots pine was examined by scanning electron microscopy following submersion in Langstone Harbour, Portsmouth, UK for periods of 2, 7, 14 and 28 days. Results indicated a slightly faster rate of biofilm formation after 2 and 7 days of exposure on untreated timber compared to CCA-treated timber, although no differences were visible between panels after 14 and 28 days exposure, or between panels treated to different CCA loadings after all exposure periods. Settlement of the serpulid Ficopomatus enigmaticus and two species of barnacles (Elminius modestus and Balanus crenatus) onto the surface of untreated and CCA-treated panels of Scots pine was examined following 4 weeks exposure in a brackish water millpond at Emsworth, West Sussex. Numbers of individuals were higher on CCA-treated panels than on untreated panels, and in the case of F. enigmaticus abundance of individuals increased with increasing preservative loadings. Early colonization by macroalgal species on the surface of CCA-treated and untreated panels of Scots pine was examined following submersion of panels in Langstone Harbour for a period of 4 weeks. Percentage cover of most species of algae was similar on the surface of CCA-treated and untreated panels, with the exception of Hincksia granulosa and Ceramium nodulosum which had significantly higher percentage cover on untreated panels. Possible explanations for the recruitment patterns are discussed.

Animals↗