Chromatic Effects Research Articles

Effects of Chromate and Non-Chromate Coating Systems on Environmentally Assisted Fatigue of an Aluminum Alloy

Fatigue crack growth testing of 2024-T3 Aluminum plate was performed using compact tension (CT) specimens with chromate and non-chromate primer paint systems to evaluate the effects of the coatings on fatigue crack growth rates. The tests were conducted in lab air and sea water environments for each of the coating systems. Standard E399 CT specimens were tested to determine the influence level of environmentally assisted cracking (corrosion fatigue) on crack growth rates and cyclic count to prescribed pre-crack and final crack lengths. Increasing stress range (ΔK) tests were conducted at 10 Hz in the range of 6.5 to 26.5 MPa\(\sqrt m\). It was determined that the coated specimens exhibited a 12% shorter total life, on average, than the bare specimens for the lab air cases. In the case of salt water exposure, the coated specimens exhibited approximately 10% life increase over the bare specimens. The number of cycles to the 2.54 mm pre-crack length for the coated specimens was all less than the cycle count for the bare tests. In each case (coated or bare), there was an increased growth rate at the lower stress ranges in the salt water environment, with the chromate system case displaying the smallest change (increase). It can be concluded that the coated specimens initiate cracks and propagate faster than the bare specimens for short cracks at low stress range, but the environmental influence on the specimens is quickly overshadowed as the cracks elongate and the rate of growth increases. The coated specimens exhibited a higher total life cycle count to final crack length for this testing.

On chromatic effects in observations of the Sun near the horizon

The observability of the “green flash” in observations of the Sun near the horizon was calculated. The calculations were conducted with consideration for chromatic refraction, atmosphere transmission, spectral sensitivity of the eye, and image blurring due to the instability and inhomogeneity of the atmosphere.

25-Gb/s optical NRZ transmission over 40 km of single-mode fiber at 1550 nm without dispersion compensation

We present a method for transmitting 25-Gb/s optical nonreturn-to-zero signals at a wavelength of 1550nm over a 40-km single-mode fiber without any dispersion compensation methods. We propose optimized self-phase modulation by varying parameters of the fiber launching power and the extinction ratio of optical non-return to zero signals to overcome severe signal distortions by the chromatic dispersion effect. Using the optimization of the self-phase modulation effect, we were able to transmit 25-Gb/s optical nonreturn-to-zero signals over a 40-km single-mode fiber, which can be applicable to passive optical networks with a single wavelength channel and a high split ratio. We demonstrated that the self-phase modulation effect can be controlled by the extinction ratio and the fiber launching power.

Anomalous focusing characteristics of nanoscale metallic waveguide array under different incident wavelengths

The chromatic aberration effect of light focusing in a periodic nanoscale metallic waveguide array (NMWA) is investigated by using the coupled-mode theory and numerical simulations. The dispersion of the coupling coefficient in the periodic NMWA is calculated. The spreading angle of surface plasmon polaritons (SPPs) is derived from the distribution of the electric field density. The numerical results demonstrate that the light focusing in the periodic NMWA exhibits an anomalous chromatic property in an appropriate wavelength range compared to a conventional microlens.

SPARCO : a semi-parametric approach for image reconstruction of chromatic objects

The emergence of optical interferometers with three and more telescopes allows image reconstruction of astronomical objects at the milliarcsecond scale. However, some objects contain components with very different spectral energy distributions (SED; i.e. different temperatures), which produces strong chromatic effects on the interferograms that have to be managed with care by image reconstruction algorithms. For example, the gray approximation for the image reconstruction process results in a degraded image if the total (u, v)-coverage given by the spectral supersynthesis is used. The relative flux contribution of the central object and an extended structure changes with wavelength for different temperatures. For young stellar objects, the known characteristics of the central object (i.e., stellar SED), or even the fit of the spectral index and the relative flux ratio, can be used to model the central star while reconstructing the image of the extended structure separately. Methods. We present a new method, called SPARCO (semi-parametric algorithm for the image reconstruction of chromatic objects), which describes the spectral characteristics of both the central object and the extended structure to consider them properly when reconstructing the image of the surrounding environment. We adapted two image-reconstruction codes (Macim, Squeeze, and MiRA) to implement this new prescription. SPARCO is applied using Macim, Squeeze and MiRA on a young stellar object model and also on literature data on HR5999 in the near-infrared with the VLTI. This method paves the way to improved aperture-synthesis imaging of several young stellar objects with existing datasets. More generally, the approach can be used on astrophysical sources with similar features such as active galactic nuclei, planetary nebulae, and asymptotic giant branch stars.

Impact of chromatic effects on galaxy shape measurements

Current and future imaging surveys will measure cosmic shear with a statistical precision that demands a deeper understanding of potential systematic biases in galaxy shape measurements than has been achieved to date.We investigate the effects of using the point spread function (PSF) measured with stars to determine the shape of a galaxy that has a different spectral energy distribution (SED) than the star.We demonstrate that a wavelength dependent PSF size, for example as may originate from atmospheric seeing or the diffraction limit of the primary aperture, can introduce significant shape measurement biases.This analysis shows that even small wavelength dependencies in the PSF may introduce biases, and hence that achieving the ultimate precision for weak lensing from current and future imaging surveys will require a detailed understanding of the wavelength dependence of the PSF from all sources, including the CCD sensors.

User-preferred color temperature adjustment for smartphone display under varying illuminants

The study aims to investigate the user-preferred color temperature adjustment for smartphone dis- plays by observing the effect of the illuminant's chromaticity and intensity on the optimal white points preferred by users. For visual examination, subjects evaluated 14 display stimuli presented on the Samsung Galaxy S3 under 19 ambient illuminants. The display stimuli were composed of 14 nuanced whites varying in color temperature from 2900 to 18,900 K. The illuminant conditions varied with combinations of color temperature (2600 to 20,100 K) and illuminance level (30 to 3100 lx) that simulated daily lighting experiences. The subjects were asked to assess the optimal level of the display color temperatures based on their mental representation of the ideal white point. The study observed a positive correlation between the illuminant color temperatures and the optimal display color temperatures (r ¼ 0.89, p < 0.05). However, the range of the color temperature of the smartphone display was much narrower than that of the illuminants. Based on the assessments by 100 subjects, a regression formula was derived to predict the adjustment of user-preferred color temperature under changing illuminant chromaticity. The formula is as follows: (DisplayT cp ¼ 6534.75 log ðIlluminantT cpÞ − 16304.68 (R 2 ¼ 0.87, p < 0.05)). Moreover, supporting previous studies on color reproduction, the effect of illuminant chro- maticity was relatively weaker under lower illuminance. The results of this experiment could be used as a theo- retical basis for designers and manufacturers to adjust user-preferred color temperature for smartphone displays under various illuminant conditions. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.OE.53.6.061708)

Study of Transmission Characteristics of Optical Pulse in the Dispersive Fiber

Chromatic dispersion and nonlinearity effect are the two important factors affecting the optical pulse which propagates in the optical fiber. The former makes the pulse broaden, the latter mainly broaden pulse spectrum. Therefore, the linear and nonlinear dispersive propagation and control of optical pulses in the fiber has always been an important research topic of concern. In this paper, Starting from the nonlinear Schrodinger equation of the optical pulse and neglecting the chromatic dispersion, under the situation of chirp and chirp-free Gaussian pulse, we analytical analyzed, calculated and simulated the frequency chirp, pulse broadening factor and waveform of the Gaussian optical pulses in dispersion fiber. And numerical studied the waveform evolution of chirp-free super-Gaussian optical pulse with distance, analyzed the influence of optical pulse propagation by dispersion in different shapes and different initial chirp.

The effect of chromate on the pitting susceptibility of AA7075-T651 studied using potentiostatic transients

The effect of chromate on metastable pitting of AA7075-T651 as determined via potentiostatic polarisation is reported. A systematic study of metastable pitting and its correlation with stable pits was conducted in various concentrations of sodium chromate (Na2CrO4), revealing the metastable pitting rate was able to provide a quantitative metric for pitting corrosion. The size and number of metastable pits decreased significantly in the presence of chromate. The present study is intended as a general baseline for the assessment of future chromate replacement technologies, as elaborated herein.

A distributed fiber vibration sensor utilizing dispersion induced walk-off effect in a unidirectional Mach-Zehnder interferometer

We propose and experimentally demonstrate a novel ultra-long range and sensitive distributed fiber vibration sensor. Only one unidirectional Mach-Zehnder interferometer (MZI) is employed in this scheme as the sensing element. In this sensor structure, we utilize chromatic dispersion-induced walk-off effect between the vibration signals sensed by two distributed feedback (DFB) lasers at different wavelengths to locate the vibration position. Vibration signals with frequencies up to 9 MHz can be detected and the spatial resolution of 31 m is achieved over 320 km of the standard single mode fiber. Monitoring multiple vibration sources can also be realized using this scheme.

Landau damping and the head–tail instability of the coupled synchro-betatron coherent oscillations

Within the hollow-bunch approximation we study variations in the stability conditions of the coupled synchro-betatron coherent oscillations due to common effects of the lattice chromaticity and of the Landau damping of such oscillations. We assume that the Landau damping of coherent oscillations is provided by octupole fields of the ring lattice. We also assume that the wakefields of the bunch decay substantially during the revolution period of particles along the closed orbit. For this reason, the memory of the bunch wakefields is ignored in this paper.

No psychological effect of color context in a low level vision task

Background: A remarkable series of recent papers have shown that colour can influence performance in cognitive tasks. In particular, they suggest that viewing a participant number printed in red ink or other red ancillary stimulus elements improves performance in tasks requiring local processing and impedes performance in tasks requiring global processing whilst the reverse is true for the colour blue. The tasks in these experiments require high level cognitive processing such as analogy solving or remote association tests and the chromatic effect on local vs. global processing is presumed to involve widespread activation of the autonomic nervous system. If this is the case, we might expect to see similar effects on all local vs. global task comparisons. To test this hypothesis, we asked whether chromatic cues also influence performance in tasks involving low level visual feature integration. Methods: Subjects performed either local (contrast detection) or global (form detection) tasks on achromatic dynamic Glass pattern stimuli. Coloured instructions, target frames and fixation points were used to attempt to bias performance to different task types. Based on previous literature, we hypothesised that red cues would improve performance in the (local) contrast detection task but would impede performance in the (global) form detection task. Results: A two-way, repeated measures, analysis of covariance (2×2 ANCOVA) with gender as a covariate, revealed no influence of colour on either task, F(1,29) = 0.289, p = 0.595, partial η 2 = 0.002. Additional analysis revealed no significant differences in only the first attempts of the tasks or in the improvement in performance between trials. Discussion: We conclude that motivational processes elicited by colour perception do not influence neuronal signal processing in the early visual system, in stark contrast to their putative effects on processing in higher areas.

The effect of chromate on the synthesis of plastid pigments and lipoquinones in Zea mays L. seedlings

Maize plants cultivated on nutrient solutions containing increasing amounts of CrO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt; (from 10&lt;sup&gt;-7&lt;/sup&gt; to 10&lt;sup&gt;-4&lt;/sup&gt; M) showed growth inhibition, strong reduction of the root system and an increase of dry matter of leaves. The highest accumulation of chromium in plant organs appeared in the roots. Chromate taken up into leaves caused changes in the content of plastid pigments and lipoquinones similar, in general, to those in senescent plants.

On Chromatic Effects in Observations of the Sun near the Horizon

On Chromatic Effects in Observations of the Sun near the Horizon

Evaluation of small suprathreshold color differences under different background colors

A psychophysical experiment under constant stimuli is conducted on a CRT display to measure the visual suprathreshold color differences for five color centers recommended by CIE under the same five background colors. The performances of four CIELAB-based, three CIECAM02-based, and two OSA-UCS-based formulas are tested. Detailed analysis results indicate the existence of chromatic crispening effect. CIEDE2000 performs best for the gray center and gray background, whereas CAM02-LCD and CAM02-UCS have the best performance for non-neutral backgrounds. CAM02-LCD significantly outperforms all other formulas for all color centers under all background colors.

Atmospheric pitting corrosion of AA7075-T6 under evaporating droplets with and without inhibitors

Pitting corrosion of polished and etched AA7075-T6 in the presence of 3.5 wt% NaCl electrolyte was investigated both with standard full immersion testing, and under evaporating electrolyte droplets in a fixed humidity environment. The effects of chromate-, vanadate-, and cerous-based corrosion inhibiting salts were also examined. A scanning Kelvin probe (SKP) was used to investigate the corrosion potential behavior in the electrolyte droplets. During immersion testing, widespread pitting at intermetallic particles was observed in uninhibited solution. Similar but less severe attack was observed with additions of 0.03 mM vanadate and cerous ions. At higher concentration of vanadate, small numbers of very large pits were found, while higher concentrations of cerous ions provided very good inhibition. Chromate provided nearly complete inhibition of corrosion in all concentrations of immersion testing. In droplet testing, corrosion potentials measured by SKP were associated with metastable pitting, inhibition/passivation, and a form of corrosion attack in which pitting at the edge of the test droplet resulted in the formation of an adjacent, secondary droplet. A model is described for the formation of the secondary droplet and associated attack, by deliquescence of water vapor due to an excess of ions from the anode diffusing to the edge of the droplet.

Effect of chromate on photosynthesis in Cr(VI)-resistant Chlorella

Chromate-resistant Chlorella spp. isolated from effluents of electroplating industry could grow in the presence of 30 μM K2Cr2O7. Since photosynthesis is sensitive to oxidative stress, chromate toxicity to photosynthesis was examined in this algal isolate. Chromate [Cr(VI)] up to 100 μM was found to stimulate photosynthesis, while 90% inhibition was found, when the cells were incubated with 1 mM Cr(VI) for 4 h. Photosystem (PS) II was inhibited by 80% and PSI by 40% after such Cr(VI) treatment. Thermoluminescence studies on cells treated with 1 mM Cr(VI) for 4 h showed that S2QA - recombination peak (Q) was shifted to higher temperature, whereas S2/S3QB - recombination peak (B) was shifted to lower temperature. These shifts indicated alga stress response in order to overcome an excitation stress resulting from the inhibition of photosynthesis by Cr(VI). The nontreated Chlorella cells kept in the dark showed periodicity of four for the Q peak (4-8°C) and B peak (34-38°C) after exposure to series of single, turnover, saturating flashes. This periodicity was lost in Cr(VI)-treated cells. Higher concentrations of Cr(VI) inhibited mainly the electron flow in the electron transport chain, inactivated oxygen evolving complex, and affected also Calvin cycle enzymes in the Cr(VI)-resistant isolates of Chlorella.

Chromatic effects in the 21 cm global signal from the cosmic dawn

The redshifted 21 cm brightness distribution from neutral hydrogen is a promising probe into the cosmic dark ages, cosmic dawn, and re-ionization. LOFAR's Low Band Antennas (LBA) may be used in the frequency range 45 MHz to 85 MHz (30>z>16) to measure the sky averaged redshifted 21 cm brightness temperature as a function of frequency, or equivalently, cosmic redshift. These low frequencies are affected by strong Galactic foreground emission that is observed through frequency dependent ionospheric and antenna beam distortions which lead to chromatic mixing of spatial structure into spectral structure. Using simple models, we show that (i) the additional antenna temperature due to ionospheric refraction and absorption are at a \sim 1% level--- 2 to 3 orders of magnitude higher than the expected 21 cm signal, and have an approximate \nu^{-2} dependence, (ii) ionospheric refraction leads to a knee-like modulation on the sky spectrum at \nu\approx 4\times plasma frequency. Using more realistic simulations, we show that in the measured sky spectrum, more than 50% of the 21 cm signal variance can be lost to confusion from foregrounds and chromatic effects. We conclude that foregrounds and chromatic mixing may not be subtracted as generic functions of frequency as previously thought, but must rather be carefully modeled using additional priors and interferometric measurements.

No psychological effect of color context ina low level vision task.

A remarkable series of recent papers have shown that colour can influence performance in cognitive tasks. In particular, they suggest that viewing a participant number printed in red ink or other red ancillary stimulus elements improves performance in tasks requiring local processing and impedes performance in tasks requiring global processing whilst the reverse is true for the colour blue. The tasks in these experiments require high level cognitive processing such as analogy solving or remote association tests and the chromatic effect on local vs. global processing is presumed to involve widespread activation of the autonomic nervous system. If this is the case, we might expect to see similar effects on all local vs. global task comparisons. To test this hypothesis, we asked whether chromatic cues also influence performance in tasks involving low level visual feature integration. Subjects performed either local (contrast detection) or global (form detection) tasks on achromatic dynamic Glass pattern stimuli. Coloured instructions, target frames and fixation points were used to attempt to bias performance to different task types. Based on previous literature, we hypothesised that red cues would improve performance in the (local) contrast detection task but would impede performance in the (global) form detection task. A two-way, repeated measures, analysis of covariance (2×2 ANCOVA) with gender as a covariate, revealed no influence of colour on either task, F(1,29) = 0.289, p = 0.595, partial η (2) = 0.002. Additional analysis revealed no significant differences in only the first attempts of the tasks or in the improvement in performance between trials. We conclude that motivational processes elicited by colour perception do not influence neuronal signal processing in the early visual system, in stark contrast to their putative effects on processing in higher areas.

Effects of Chromate and Molybdate Ions On Scratch Repassivation Behavior of Precipitation Hardened Aluminum Alloys

not Available.