Slow Dark Research Articles

Lab- and pilot- scale evaluation of bacterial inactivation and reactivation influenced by UV-LEDs arrangements in continuous flow water disinfection reactors

In the recent years, UV-LED has emerged as an alternative UV source due to its distinguish advantages. One of the primary benefits of UV-LEDs is their ability to facilitate fine-tuned regulation of UV radiation utilization in disinfection systems, which could increase the effective UV fluence in the reactor and thus improve the disinfection efficiency compared with conventional UV disinfection devices. This study evaluated the inactivation and reactivation performance of continuous flow UV-LED (265 nm) disinfection reactor with four different designs of UV-LEDs arrangement under both lab- and pilot- scale testing conditions. Lab-scale tests showed that UV-LEDs at the outlet position delivered a much higher E.coli disinfection efficiency compared with other three arrangements (UV-LEDs at inlet, center, and separated positions) under various of UV-LED outputs and flowrates. Mechanisms analysis indicated that the improved disinfection efficiency was because UV radiation was applied to the lower velocity region in the reactor, leading to a longer effective UV exposure time and thus a higher UV fluence generated. Sub-germicidal levels of UV irradiation prior to the high UV fluence region could also improve the overall disinfection efficiency for separated and outlet arrangement, with synergy values of 0.21 log (16.6 % of overall log reduction) and 0.53 log (21.4 % of overall log reduction) generated. The reactivation experiments showed that the inlet arrangement led to the highest photo repair rates. Dark repair was not affected by the different UV-LEDs arrangement due to the relatively slow dark repair rates. The key findings in the lab-scale tests were then validated in a small-scale (Total flowrate was 13.3 L/min) recirculatory aquaculture system (RAS) system for shrimp farming. The inactivation and reactivation results under pilot-scale tests were consistent with the lab-scale testing results, showing that UV-LEDs at outlet position provided an average total bacteria disinfection efficiency of 1.84 logs in an 8 week testing period, which was more than twice of that for the inlet position. After disinfection, samples from the outlet arrangement also exhibited at least 26.5 % less photoreactivation percentage compared with that when LEDs were at the inlet position. These findings proposed an optimal design of UV-LEDs arrangement for UV disinfection reactors and verified this design in pilot-scale testing condition. This information is important for future optimizations of UV LED disinfection system design.

Vision through Healthy Aging Eyes.

As life expectancy grows, so too will the number of people adversely affected by age. Although it is acknowledged that many conditions and diseases are associated with age, this mini-review will present a current update of the various visual changes that generally occur in healthy individuals disregarding the possible effects of illness. These alterations influence how the world is perceived and in turn can affect efficiency or the ability to perform ordinary daily tasks such as driving or reading. The most common physical developments include a decreased pupil size and retinal luminance as well as changes both in intercellular and intracellular connections within the retina along the pathway to the visual cortex and within the visual cortex. The quantity and the physical location of retinal cells including photoreceptors, ganglion and bipolar retinal cells are modified. The clarity of intraocular organs, such as the intraocular lens, decreases. These all result in common visual manifestations that include reduced visual acuity, dry eyes, motility changes, a contraction of the visual field, presbyopia, reduced contrast sensitivity, slow dark adaptation, recovery from glare, variation in color vision and a decreased visual processing speed. Highlighting these prevalent issues as well as current and possible future innovations will assist providers to formulate treatments and thereby conserve maximum independence and mobility in the modern mature population.

Mizuo-Nakamura phenomenon in an Indian male.

Key Clinical Message The authors present a 20‐year‐old myopic male who showed golden color of fundus (Mizuo‐Nakamura phenomenon) in light and normal color after long dark adaptation. This phenomenon is associated with an abnormally slow dark adaptation and is typically noted in Oguchi disease, a variant of congenital stationary night blindness.

The slow light and dark oscillation of the clinical electro‐oculogram

BackgroundThe standing potential of the eye exhibits a slow damped oscillation under light and dark conditions that continues for at least 80 minutes. However, our understanding of the relationship between the slow dark and light oscillation has not been previously studied. The aim of this study was to explore through regression analysis a model of these oscillations in order to establish if they may have the same underlying cellular generators.MethodsHealthy participants undertook recordings of the standing potential using the electro‐oculogram for 100 minutes. To explore the light oscillation, participants (n = 8) were dilated and performed an extended electro‐oculogram protocol consisting of 15 minutes dark adaptation and 85 minutes of white light adaptation at 100 cd/m2. For the dark oscillation, participants (n = 11) undertook the electro‐oculogram for 100 minutes in complete darkness. Both sessions began with pre‐adaptation to 30 cd/m2 of white light for five minutes. Non‐parametric statistics were used to evaluate all data.ResultsRatios of the dark and light oscillations showed a significantly greater dampening of the dark oscillation compared to the light oscillation (p < 0.000). Regression analysis using a five‐factor damped sine function revealed significant differences in the parameters governing the dampening (p = 0.005) and period (p = 0.009) of the functions (R2 > 0.874). There were no significant differences in the dark trough amplitude.ConclusionThe results support a different underlying physiological mechanism for the light and dark oscillation of the clinical electro‐oculogram. Future work will need to establish how the dark oscillation and dark trough of the clinical electro‐oculogram arise.

Characterization of Rod Function Phenotypes Across a Range of Age-Related Macular Degeneration Severities and Subretinal Drusenoid Deposits

PurposeTo examine spatial changes in rod-mediated function in relationship to local structural changes across the central retina in eyes with a spectrum of age-related macular degeneration (AMD) disease severity.MethodsParticipants were categorized into five AMD severity groups based on fundus features. Scotopic thresholds were measured at 14 loci spanning ±18° along the vertical meridian from one eye of each of 42 participants (mean = 71.7 ± 9.9 years). Following a 30% bleach, dark adaptation was measured at eight loci (±12°). Rod intercept time (RIT) was defined from the time to detect a −3.1 log cd/m2 stimulus. RITslope was defined from the linear fit of RIT with decreasing retinal eccentricity. The presence of subretinal drusenoid deposits (SDD), ellipsoid (EZ) band disruption, and drusen at the test loci was evaluated using optical coherence tomography.ResultsScotopic thresholds indicated greater rod function loss in the macula, which correlated with increasing AMD group severity. RITslope, which captures the spatial change in the rate of dark adaptation, increased with AMD severity (P < 0.0001). Three rod function phenotypes emerged: RF1, normal rod function; RF2, normal scotopic thresholds but slowed dark adaptation; and RF3, elevated scotopic thresholds with slowed dark adaptation. Dark adaptation was slowed at all loci with SDD or EZ band disruption, and at 32% of loci with no local structural changes.ConclusionsThree rod function phenotypes were defined from combined measurement of scotopic threshold and dark adaptation. Spatial changes in dark adaptation across the macula were captured with RITslope, which may be a useful outcome measure for functional studies of AMD.

Letter re: Transient smartphone blindness: Relevance to misdiagnosis in neurologic practice.

A few observations regarding transient smartphone blindness (TSB) being misdiagnosed as multiple sclerosis (MS), as noted by Drs. Sathiamoorthi and Wingerchuk,1 require further discussion: 1. While optic neuritis cases may exhibit amaurosis fugax, diagnosis requires visual decline, relative afferent papillary defect, color vision or visual field changes, and pain during ocular movements with or without changes in the optic disc on funduscopy. Therefore, the ocular features of the presented case did not support the diagnosis of optic neuritis.1 We agree that MS diagnosis requires careful consideration of clinical features and clinical examination in addition to MRI features. 2. Binocular vision has the advantage of increased visual field, stereopsis, compensation for blind spot, and improved visuomotor functions.2 Monocular viewing is uncommon in humans with binocular vision, thus the clinical relevance of TSB needs further evaluation.3 3. Differential visual perception may occur with monocular exposure to any bright object, not only a smartphone. 4. Slow dark adaptation is a feature of diseases affecting the retinoid cycle and signal transduction or transmission of rod photoreceptors.4,5 Vitamin A deficiency and some forms of congenital stationary blindness, which may have an apparently normal fundus, may need to be ruled out in cases with exaggerated TSB.

Two narrow dark polaritons in triple-well microcavity based on double tunneling induced transparency

In this paper, we propose and demonstrate that two dark polaritons can be generated in a microcavity that several periods of asymmetric triple-quantum wells are embedded in. They are created by the intracavity coherent effects based on tunneling induced transparency and can be switched by using an external laser. The group time delay of this system is calculated to show the slow dark polaritons. The results have potential applications in all-optical switching and buffering in nano-scale.

Slowed dark adaptation in older eyes; effect of location

PurposeThe rate of rod sensitivity recovery following a photobleach is a basic measure of the integrity of the outer retina. Rods are selectively impaired in aging and many disorders of the retina, notably Age-Related Macular Degeneration (AMD). It is not known for certain whether the age-related deficit is a pan-retinal effect or if there are localised regions of impaired rod function. To address this important issue a dual arc stimulus was developed that samples sensitivity recovery in two retinal locations. MethodsArc-shaped stimuli were presented on a black CRT screen at two locations, in the inferior visual field. Following a bleach, which was localised to the stimuli, recovery of sensitivity was measured using a modified method of adjustment technique. Neutral density filters were used to extend the luminance range of the CRT. Sensitivity recovery functions were fitted by non-linear regression to a seven-parameter model. ResultsPairs of sensitivity recovery functions were generated from the stimuli. The cone phases of these functions were identical. The slopes of the S2 sections of the curves were steeper for the outer stimuli for both young (p < 0.001) and older (p = 0.003) observers. The difference between the two was the same for the two groups. The α point was reached slightly earlier for the young observers and with the outer stimulus but neither of these effects reached statistical significance. The β point occurred earlier for the outer stimuli and this effect was statistically significant only for the older group. ConclusionsThe method places minimal demands on observers. The fact that rod sensitivity recovery is slowed in the older normal eye to the same extent in the two locations suggests that this deficit may be uniform across the retina. As there are localised losses in scotopic function in AMD, the technique is ideally suited to distinguishing impaired recovery dynamics due to normal ageing from those caused by disease.

Why rods and cones?

Under twenty-first-century metropolitan conditions, almost all of our vision is mediated by cones and the photopic system, yet cones make up barely 5% of our retinal photoreceptors. This paper looks at reasons why we additionally possess rods and a scotopic system, and asks why rods comprise 95% of our retinal photoreceptors. It considers the ability of rods to reliably signal the arrival of individual photons of light, as well as the ability of the retina to process these single-photon signals, and it discusses the advantages that accrue. Drawbacks in the arrangement, including the very slow dark adaptation of scotopic vision, are also considered. Finally, the timing of the evolution of cone and rod photoreceptors, the retina, and the camera-style eye is summarised.

Photolysis of natural β-triketonic herbicides in water

The fate of four natural β-triketones (leptospermone, isoleptospermone, grandiflorone and flavesone, pKa = 4.0–4.5) in aqueous solution, in the dark and upon simulated solar light irradiation was investigated. In anionic form, β-triketones undergo slow dark oxidation and photolysis with polychromatic quantum yields varying from 1.2 × 10−4 to 3.7 × 10−4. Leptospermone and grandiflorone are the most photolabile compounds. In molecular form, β-triketones are rather volatile. Polychromatic quantum yields between 1.2 × 10−3 and 1.8 × 10−3 could be measured for leptospermone and grandiflorone. They are 3–5 times higher than for the anionic forms. Photooxidation on the carbon atom bearing the acidic hydrogen atom is the main oxidation reaction, common to all the β-triketones whatever their ionization state. However, leptospermone shows a special photoreactivity. In molecular form, it mainly undergoes photoisomerization. Based on this work, the half-lives of β-triketones in surface waters should be comprised between 7 and 23 days.

Brightness discrimination in the South African fur seal (Arctocephalus pusillus)

Underwater, the contrast between object and background is much larger reduced with increasing distance between object and observer than in air. For marine predators, such as pinnipeds, it would therefore be advantageous to possess a high sensitivity for brightness differences, since this would increase the distance at which prey can be detected visually. Few studies have examined the brightness discrimination thresholds of pinnipeds. Two studies with phocid seals have confirmed low brightness discrimination thresholds in pinnipeds whereas the threshold obtained for the South African fur seal seems to be twice as high as that of the phocids. However, the experiments with the South African fur seal have been conducted under inadequate conditions which likely resulted in an underestimation of the brightness discrimination ability of this species. The study at hand reinvestigated the brightness discrimination threshold of the South African fur seal under well controlled conditions. In a two alternative forced choice task, one fur seal was trained to indicate the position of the brighter of two gray discs presented on a black background on a monitor. The thresholds were determined for 11 standard intensities each tested against 8 lower comparison intensities. It was found that the fur seal was able to perceive brightness differences of 8-10%, which is better than the phocid species tested so far. For low standard intensities, however, the threshold increased which could to be due to a relative slow dark adaptation rate of the fur seal. The results are discussed in terms of the relevance of visual information for pinnipeds during foraging dives and are directly compared to the results obtained for the harbor seal which has been tested under the same conditions as the fur seal in a previous study.

Strobes: An Oscillatory Combustion

Strobe compositions belong to the class of solid combustions. They are mixtures of powdered ingredients. When ignited, the combustion front evolves in an oscillatory fashion, and flashes of light are produced by intermittence. They have fascinated many scientists since their discovery at the beginning of the 20th century. However, the chemical and physical processes involved in this curious oscillatory combustion remain unknown. Several theories have been proposed: One claims that two different reactions occur: one during the slow dark phase and another during the fast flash phase. The alternation between the phases is ascribed to heat variations. Other theories suggest that the formation of intermediate species during the dark phase and the change of phase are caused by variations in their concentration. A ternary strobe composition with ammonium perchlorate, magnalium, and barium sulfate is analyzed. The role of barium sulfate is studied by replacing it by other metal sulfates that have different physical properties (melting points), and the burning of the compositions is recorded with a high-speed camera and a spectrometer coupled with a charge-coupled device (CCD) camera. Experimental results show noticeable differences in the physical and chemical processes involved in the strobe reactions.

Structural Basis for the Slow Dark Recovery of a Full-Length LOV Protein from Pseudomonas putida

Blue-light photoreceptors containing light–oxygen–voltage (LOV) domains regulate a myriad of different physiological responses in both eukaryotes and prokaryotes. Their light sensitivity is intricately linked to the photochemistry of the non-covalently bound flavin mononucleotide (FMN) chromophore that forms a covalent adduct with a conserved cysteine residue in the LOV domain upon illumination with blue light. All LOV domains undergo the same primary photochemistry leading to adduct formation; however, considerable variation is found in the lifetime of the adduct state that varies from seconds to several hours. The molecular mechanism underlying this variation among the structurally conserved LOV protein family is not well understood. Here, we describe the structural characterization of PpSB1-LOV, a very slow cycling full-length LOV protein from the Gram-negative bacterium Pseudomonas putida KT2440. Its crystal structure reveals a novel dimer interface that is mediated by N- and C-terminal auxiliary structural elements and a unique cluster of four arginine residues coordinating with the FMN-phosphate moiety. Site-directed mutagenesis of two arginines (R61 and R66) in PpSB1-LOV resulted in acceleration of the dark recovery reaction approximately by a factor of 280. The presented structural and biochemical data suggest a direct link between structural features and the slow dark recovery observed for PpSB1-LOV. The overall structural arrangement of PpSB1-LOV, together with a complementary phylogenetic analysis, highlights a common ancestry of bacterial LOV photoreceptors and Per-ARNT-Sim chemosensors.

Photometry in the dark: time dependent visibility of low intensity light sources

This paper aims at describing the perceived brightness of persistent luminescent materials for emergency signage. In case of emergency, typically, a fully light adapted person is left in the dark, except for the emergency sign. The available photometric models cannot describe visibility of such light source, as they do not consider the slow dark adaptation of the human eye. The model proposed here fully takes into account the shift from photopic to scotopic vision, the related shift in spectral sensitivity and the dark adaptation. The resulting metric is a 'visibility index' and preliminary tests show that it more realistically describes the perceived brightness of persistent luminescent materials than the common photometric standards.

Coupling Between the Retinal Thermal Isomerization and the Glu194 Residue of Bacteriorhodopsin†

Glu194 is a residue located at the end of F helix on the extracellular side of the light-induced proton pump bacteriorhodopsin (BR). Currently, it is well recognized that Glu194 and Glu204 residues, along with water clusters, constitute the proton release group of BR. Here we report that the replacement of Glu194 for Gln affects not only the photocycle of the protein but also has tremendous effect on the all-trans to 13-cis thermal isomerization. We studied the pH dependence of the dark adaptation of the E194Q mutant and performed HPLC analysis of the isomer compositions of the light- and partially dark-adapted states of the mutant at several pH values. Our data confirmed that E194Q exhibits extremely slow dark adaptation over a wide range of pH. HPLC data showed that a significantly larger concentration of all-trans isomer was present in the samples of the E194Q mutant even after prolonged dark adaptation. After 14 days in the dark the 13-cis to all-trans ratio was 1:3 in the mutant, compared to 2:1 in the wild type. These data clearly indicate the involvement of Glu194 in control of the rate of all-trans to 13-cis thermal isomerization.

Comment on “Stable and unstable vector dark solitons of coupled nonlinear Schrödinger equation: Application to two-component Bose-Einstein condensates

In a recent paper, V. A. Brazhnyi and V. V. Konoto [Phys. Rev. E 72, 026616 (2005)] investigated the dynamics of vector dark solitons in two-component Bose-Einstein condensates. In the small amplitude limit, they deduced a coupled Korteweg-de Vries equation from the coupled Gross-Pitaevskii equations. They found that two branches of (slow and fast) dark solitons corresponding to the two branches of the sound waves exist. The slow solitons, corresponding to the lower branch of the acoustic wave, appear to be unstable and transform during the evolution into the stable fast solitons (corresponding to the upper branch of the dispersion law). However, our discussion shows that these results are incorrect.

Slow dark deactivation of Arabidopsis chloroplast ATP synthase caused by a mutation in a nonplastidic SAC domain protein

Coupling factor slow recovery (cfs) is a recessive mutant of Arabidopsis with anomalous ATP synthase activation/deactivation characteristics as well as a distinct growth phenotype. The most significant feature of this mutant is that the dark-adapted deactivation of ATP synthase is a very slow relative to the wild type, indicating interference with ATP synthase regulation. Physical mapping of the mutation delimited it to a region in a pair of bacterial artificial chromosome clones. Examination of T-DNA insertion lines of all 34 putative genes located in this region identified two homozygous T-DNA insertion lines of the same gene, At3g59770, possessing phenotypes indistinguishable from the cfs mutant. At3g59770 had been previously identified as suppressor of actin 9 (SAC9), a protein with a SAC domain, a protein-protein interaction module containing two conserved tryptophans known as a WW domain, and an ATP/GTP-binding site motif A. Sequence analysis of cfs revealed a point mutation of G to A resulting in an amino acid substitution from tryptophan to STOP, thereby coding a truncated protein. Real-time-PCR amplification of the gene specific fragments showed that the T-DNA mutants did not have full-length transcripts whereas the cfs mutant transcribed a full-length mutated transcript. Further investigation of SAC9 RNA expression levels in different tissues of wild-type plants by RT-PCR revealed the highest expression in leaves. SAC 9 dysfunction interferes with ATP synthase deactivation, possibly by an alteration in phosphoinositide signaling inducing a stress mimicry response.

Exact numerical solutions for dark waves on the discrete nonlinear Schrödinger equation

In this paper we study numerically existence and stability of exact dark waves on the (nonintegrable) discrete nonlinear Schrödinger equation for a finite one-dimensional lattice. These are solutions that bifurcate from stationary dark modes with constant background intensity and zero intensity at a site, and whose initial state translates exactly one site each period of the internal oscillations. We show that exact dark waves are characterized by an oscillatory background whose wavelength is closely related with the velocity. Faster dark waves require smaller wavelengths. For slow enough velocity dark waves are linearly stable, but when trying to continue numerically a solution towards higher velocities bifurcations appear, due to rearrangements in the oscillatory tail in order to make possible a decreasing of the wavelength. However, in principle, one might control the stability of an exact dark wave adjusting a phase factor which plays the role of a discreteness parameter. In addition, we also study the regimes of existence and stability for stationary discrete gray modes, which are exact solutions with phase-twisted constant-amplitude background and nonzero minimum intensity. Also such solutions develop envelope oscillations on top of the homogeneous background when continued into moving phase-twisted solutions.

Light-Induced Formation of Silver Particles and Clusters in Crosslinked PVA/PAA Films

Thin films able to sustain an efficient photoreduction of Ag+ ions with 350 nm photons in air were prepared by crosslinking poly(vinyl alcohol) with glutaraldehyde in the presence of poly(acrylic acid). Standard colloid techniques served as screening methods for the selection of polymer compositions yielding films with desired properties. When present at high concentrations, Ag+ ions were reduced at room temperature in the films by poly(vinyl alcohol) but poly(acrylic acid) inhibited the slow dark reaction. Optical signals with maxima above 400 nm resulted from both reduction processes. The available evidence confirmed that they originated from nanometer-sized metal particles and is inconsistent with results for other proposed chromophores. An additional absorption centered at 280 nm that formed only under illumination was assigned to Ag3+ clusters. Small Ag crystallites with similar size distributions and with an average diameter of 5 nm were the main product of the photoreduction in non-crosslinked or c...

Dark adaptation and the retinoid cycle of vision.

Following exposure of our eye to very intense illumination, we experience a greatly elevated visual threshold, that takes tens of minutes to return completely to normal. The slowness of this phenomenon of "dark adaptation" has been studied for many decades, yet is still not fully understood. Here we review the biochemical and physical processes involved in eliminating the products of light absorption from the photoreceptor outer segment, in recycling the released retinoid to its original isomeric form as 11-cis retinal, and in regenerating the visual pigment rhodopsin. Then we analyse the time-course of three aspects of human dark adaptation: the recovery of psychophysical threshold, the recovery of rod photoreceptor circulating current, and the regeneration of rhodopsin. We begin with normal human subjects, and then analyse the recovery in several retinal disorders, including Oguchi disease, vitamin A deficiency, fundus albipunctatus, Bothnia dystrophy and Stargardt disease. We review a large body of evidence showing that the time-course of human dark adaptation and pigment regeneration is determined by the local concentration of 11-cis retinal, and that after a large bleach the recovery is limited by the rate at which 11-cis retinal is delivered to opsin in the bleached rod outer segments. We present a mathematical model that successfully describes a wide range of results in human and other mammals. The theoretical analysis provides a simple means of estimating the relative concentration of free 11-cis retinal in the retina/RPE, in disorders exhibiting slowed dark adaptation, from analysis of psychophysical measurements of threshold recovery or from analysis of pigment regeneration kinetics.