Dim Light Conditions Research Articles

Photovoltaic performance of Organic Photovoltaics for indoor energy harvester

Wireless sensor network becomes widespread into home and offices to keep them comfort and save the energy. The battery-less wireless sensor nodes need the high performance indoor solar cells for stable and sustainable operation. Organic Photovoltaics (OPV) has great indoor photovoltaic performance because ultra-thin organic layer has strong absorption against the UV–visible spectrum that is good spectral matching with indoor lightings. In this study, OPV module has 8 cells in series and same size as the conventional amorphous silicon solar cells (a-Si) for indoor light harvesting. OPV and a-Si are measured their photovoltaic performance under the fluorescent light and demonstrated for energy harvester of wireless sensor network. The output power of OPV and a-Si is 43.4 μW cm−2 and 28.5 μW cm−2 at fluorescent light 1000lux respectively. The data transmission rate of the wireless sensor node driven by OPV is 30–40% improved under the dim light condition compared to a-Si.

0688 IMPACT OF CIRCADIAN MISALIGNMENT AND BMI ON GLUCOSE DYSREGULATION IN NIGHT-SHIFT WORKERS

Epidemiological studies suggests that night shift workers are at increased risk for obesity and diabetes, and simulated shift work studies in day workers have implicated circadian misalignment as a culprit for reduced glucose tolerance. However, this has not been tested in actual night shift workers. To better understand the role of circadian misalignment on glucose dysregulation, we examined glucose tolerance in a sample of fixed night shift workers. Thirty fixed night shift workers participated in this study. All subjects were given an eight-hour opportunity to sleep upon arrival at the lab, and remained under dim-light conditions for 24 hours. An oral glucose tolerance test was administered two hours after awakening. The change in glucose from fasting to one hour after glucose intake, and from fasting to two hours after glucose intake were measured. Melatonin was also assayed via hourly salivary samples, and circadian phase was indexed using the dim light melatonin onset (DLMO). Analyses included years of night shift work as a covariate. Partial correlations controlling for years of shift work indicated that DLMO was not significantly associated with change in glucose tolerance at one-hour, r(27) = .07, p>.05, or at two-hour, r(27) = -.24, p>.05. However, DLMO was significantly associated with glucose tolerance when accounting for weight. Specifically, overweight shift workers (BMI ≥ 26) with earlier DLMOs showed lower glucose tolerance at the two-hour time point, r (15) = -.46, p<.05, compared to subjects with healthy weight, r (9) = .06, p>.05. Results suggest that circadian misalignment alone may not be a significant predictor for glucose dysregulation, but instead may interact with other risk factors for diabetes, such as weight. Thus, increased risk for diabetes in night shift workers should not be generalized, but rather considered only when circadian disturbance is paired with pre-existing risk factors. Our project was funded by TEVA pharmaceuticals.

Species-specific development of retinal architecture in elopomorph fishes: adaptations for harvesting light in the dark

Elopomorph fishes are distinguished in part by a shared leptocephalus larval form. These glass-clear, ribbon-like larvae are remarkably similar across the elopomorpha, yet they mature to radically different forms as adults. Along the timecourse of development, they transition through a variety of spectrally distinct habitats, occupying very different temporal niches as adults - some diurnal predators in high-light environments, others crepuscular, and others nocturnal. We found that in concert with these changes, the retinas of a variety of elopomorph fish change in similarly dramatic ways over the course of development. While the mature bonefish [Albula vulpes (Linnaeus,1758)] retina is specialized for visual tasks in a high-light environment, the Atlantic tarpon (Megalops atlanticus Valenciennes, 1847) and ladyfish (Elops saurus Linnaeus,1766) exhibit multiple specializations for function at night or otherwise in very dim light conditions. These include stacked rod photoreceptors that are gathered into massive bundles, retinomotor movement of photoreceptor outer segments, and a highly reflective tapetum. In the adult form, the speckled worm eel (Myrophis punctatus Lutken, 1852) maintains a retina with nearly all rods. The dramatic divergence among taxa over the course of development produces species with distinctly specialized visual capabilities. Moreover, the ability to change over the course of development may underlie the capacity for resilience in the face of anthropogenic insults, including light pollution in increasingly developed coastal zones. On the other hand, if light history can drive retinal change, exposure to artificial light at night may be detrimental to the survival of individuals that move between light-polluted and naturally dark locations.

The effect of light intensity on performance of larval pike-perch (Sander lucioperca)

In this work performance parameters of larval pike-perch (Sander lucioperca) reared under four different light intensities (100, 500, 1000 and 2500lx) until 21days post hatch (dph) were investigated. As performance parameters change in length and weight, swim bladder inflation, feed consumption, natural mortality, stress induced mortality and RNA-DNA ratio were measured. Aim was to investigate the influence of light intensity on pike-perch performance during the first three weeks of larval rearing. Significant differences were found in natural and stress induced mortality as well as in weight growth. No single light exposure level combined optimal performance of all tested performance parameters. Highest light intensity of 2500lx showed good weight growth but an increase in stress induced mortality. Bright light of 500 and 1000lx intensity was found to improve growth and stress mortality whereas dim light conditions of 100lx showed significantly lower natural mortality. Thus data suggested that most favorable illumination during larval pike-perch rearing comprise a tradeoff between optimal natural mortality under dim light conditions (100lx) or optimal larval growth and stress resistance under bright light conditions (500 and 1000lx). It is shown that high light intensities during larval rearing can be beneficial for pike-perch rearing if offspring supply is not limited.

Photoreceptor Transplantation into the Degenerative Retina

Vision impairment and blindness due to photoreceptor loss represents one of the major causes for disability in industrialized societies. Whereas rod photoreceptors allow vision under dim light conditions, cone photoreceptors provide high-acuity vision in daylight conditions and color detection. Several therapeutic strategies are currently developed to repair vision loss, including cell-based interventions. Within the last decade, major progress regarding the replacement of photoreceptors by transplantation has been made in pre-clinical animal models. This includes defining the necessary conditions, like the optimal ontogenetic stage of transplantable donor photoreceptors, cell-specific enrichment procedures and robust transplantation technologies. Moreover, first studies provided evidence for functional improvements by photoreceptor transplantation in mouse models of retinal dysfunction. Furthermore, advances in cell culture technology were made by introducing methods to generate photoreceptor-containing retinal organoids, derived from pluripotent stem cells, that provide theoretically unlimited sources for the production of photoreceptor transplants. Interestingly, the recently identified transfer of cytoplasmic material between donor and host photoreceptors might represent an additional treatment option for cell transplantation approaches. Within this review, we focus on the main developments within the photoreceptor transplantation field and discuss important achievements, challenges and hurdles to develop photoreceptor transplantation towards clinical applications.

Can tryptophan supplement intake at breakfast enhance melatonin secretion at night?

BackgroundTryptophan (TRP) is an essential amino acid, and it has been suggested that TRP intake at breakfast combined with daytime bright light exposure can increase nocturnal melatonin secretion. However, the mechanisms involved are not yet clear. The aim of this study was to examine the effect of TRP supplement intake at breakfast on nocturnal melatonin secretion under different daytime light intensities in humans.MethodTwelve subjects (aged 21.3 ± 3.0 years, mean ± standard deviation) participated in a random order in experimental sessions lasting 3 days under four conditions in a laboratory setting. The four conditions were TRP*Bright, Placebo*Bright, TRP*Dim, and Placebo*Dim. A TRP capsule (1000 mg) or a placebo starch capsule (1000 mg) were taken at breakfast. In addition, during the daytime (07:00–18:00), the subjects were asked to stay under different light intensities: >5000 lx (bright) or <50 lx (dim). Saliva samples were collected for measuring the concentration of melatonin. The time courses of melatonin concentration and dim light melatonin onset (DLMO) were compared among the four conditions using repeated measurements analysis of variance (ANOVA).ResultNocturnal melatonin concentrations in the bright light condition tended to be higher than in the dim light condition (main effect of light: p = .099). Moreover, in the bright light condition, the change in DLMO between baseline and after the intervention was significantly higher than that in the dim light condition (main effect of light: p <.001). However, the ANOVA results indicated no significant effect of TRP intake on melatonin secretion.ConclusionOur findings indicated that intake of 1000 mg of TRP at breakfast on 1 day did not change nocturnal melatonin secretion, even though TRP is the precursor of melatonin. In contrast, daytime bright light exposure increased nocturnal melatonin secretion and advanced the phase of melatonin onset. Therefore, TRP supplementation, unlike exposure to daytime bright light, does not acutely affect biological rhythm and sleep in humans.Trial registrationUMIN Clinical Trial Registry: UMIN000024121

Rebuilding the Missing Part-A Review on Photoreceptor Transplantation.

Vision represents one of the main senses for humans to interact with their environment. Our sight relies on the presence of fully functional light sensitive cells – rod and cone photoreceptors — allowing us to see under dim (rods) and bright (cones) light conditions. Photoreceptor degeneration is one of the major causes for vision impairment in industrialized countries and it is highly predominant in the population above the age of 50. Thus, with the continuous increase in life expectancy it will make retinal degeneration reach an epidemic proportion. To date, there is no cure established for photoreceptor loss, but several therapeutic approaches, spanning from neuroprotection, pharmacological drugs, gene therapy, retinal prosthesis, and cell (RPE or photoreceptor) transplantation, have been developed over the last decade with some already introduced in clinical trials. In this review, we focus on current developments in photoreceptor transplantation strategies, its major breakthroughs, current limitations and the next challenges to translate such cell-based approaches toward clinical application.

야간 수면 중 약한 인공 빛 노출이 피로도에 미치는 영향

목 적 : 야간 빛 노출은 현대 사회에서 만연해 있으나 야간 수면 중 약한 빛 노출(dim artificial light at night, dALAN)이 피로도에 미치는 영향은 잘 인지되고 있지 않다. 본 연구에서는 수면 중 약한 빛 노출이 인간의 피로도에 어떠한 영향을 주는가를 살펴보고자 하였다. 방 법 : 21세에서 29세까지의 건강한 남성 지원자 총 30명을 연구에 모집하였다. 그들은 빛 강도에 따라 두 그룹(Group A : 5 lux와 Group B : 10 lux)으로 무작위 배정되었다. 연구 결과 자료는 빛 노출이 없는 밤(Night 1)과 두 가지 다른 약한 빛(5 혹은 10 lux)에 노출된 밤(Night 2) 다음 날 자가 보고된 피로도 척도를 통해 수집하였다. 결 과 : 야간 수면 중 약한 빛 노출은 전반적인 피로도(F = 19.556, p < 0.001)와 안구 불편감(F = 5.671, p = 0.028)의 증가와 유의하게 연관성이 있었다. 결 론 : 본 연구팀에서는 야간 수면 중 약한 빛 노출이 인간의 피로도에 일부 측면에서 영향을 준다는 것을 확인하였다. 이러한 결과들은 야간 수면 중 약한 빛 노출이 인간의 피로도에 부정적인 영향을 준다는 것을 의미한다. Objectives: Exposure to light at night has become pervasive in modern society. The impact of dim artificial light at night (dALAN) exposure on sleep and fatigue is not well recognized. We aim to study the impact of dALAN exposure during sleep on human fatigue. Methods: 30 healthy young male volunteers from 21 to 29 years old were enrolled in the study. They were randomly divided into two groups depending on light intensity (Group A : 5 lux and Group B : 10 lux). Data were gathered from each participant after each night with no light (Night 1) followed by the next night (Night 2) with two different dim light conditions (5 or 10 lux) by means of self-reported fatigue scale. Results: Exposure to dALAN during sleep was significantly associated with increased overall fatigue (F = 19.556, p < 0.001) and ocular discomfort (F = 5.671, p = 0.028). Conclusion: We found that dALAN during sleep likely affects human fatigue in some aspects. These findings indicate that dALAN during sleep exerts a negative effect on human fatigue.

Effects of bright light exposure during daytime on peripheral clock gene expression in humans.

Light is the strongest synchronizer controlling circadian rhythms. The intensity and duration of light change throughout the year, thereby influencing body weight, food preferences, and melatonin secretion in humans and animals. Although the expression of clock genes has been examined using human samples, it currently remains unknown whether bright light during the daytime affects the expression of these genes in humans. Therefore, we herein investigated the effects of bright light exposure during the daytime on clock gene expression in the hair follicular and root cells of the human scalp. Seven healthy men (20.4±2.2years old; 172.3±5.8cm; 64.3±8.5kg; BMI 21.7±3.1kg/m2, mean±SD) participated in this study. Subjects completed 3-day experimental sessions twice in 1month during which they were exposed to bright and dim light conditions. The mRNA expression of Per1-3, Cry1-2, Rev-erb-α (Nr1d1), Rev-erb-β (Nr1d2), and Dec1 was analyzed using branched DNA probes. No significant changes were observed in the expression of Per1, Per2, Per3, Cry1, Cry2, Rev-erb-α (Nr1d1), or Dec1 following exposure to bright light conditions. However, the expression of Rev-erb-β (Nr1d2) tended to be stronger under bright light than dim light conditions. These results suggest that the bright light stimulus did not influence the expression of clock genes in humans. Long-lasting bright light exposure during the daytime may be required to change the expression of clock genes in humans.

Metal-organic framework/sulfonated polythiophene on carbon cloth as a flexible counter electrode for dye-sensitized solar cells

Metal-organic framework (MOF-525) is firstly introduced as the electro-catalyst for the counter electrode (CE) of a dye-sensitized solar cell (DSSC). When MOF-525 was mixed with the conductive binder of sulfonated-poly(thiophene-3-[2-(2-methoxyethoxy)-ethoxy]-2,5-diyl) (s-PT), a composite film of MOF-525/s-PT was successfully deposited on a flexible substrate, carbon cloth (CC). The one-dimensional carbon fibers in CC were intended to provide oriented electron transfer pathways as a conductive core, and the composite film of MOF-525/s-PT covered on each carbon fiber in CC was designed to trigger the reduction of I3− as an electro-catalytic shell. Thus, a hierarchical electron transfer network was established.In the MOF-525 nanoparticle, its nodes (zirconium oxide) and linkers (meso-tetra(4-carboxyphenyl)porphyrin) were both verified to function as the electro-catalytic active sites for I3− reduction. The best MOF-525/s-PT composite counter electrode rendered 8.91±0.02% to its DSSC, showing the promising potential to replace traditional platinum (8.21±0.02%). At dim light condition (10mWcm–2), the best cell with MOF-525/s-PT composite CE shows a great cell efficiency (η) of 9.75%, which is higher than that of the cell measured at 100mWcm–2.

Genetically Blocking the Zebrafish Pineal Clock Affects Circadian Behavior.

The master circadian clock in fish has been considered to reside in the pineal gland. This dogma is challenged, however, by the finding that most zebrafish tissues contain molecular clocks that are directly reset by light. To further examine the role of the pineal gland oscillator in the zebrafish circadian system, we generated a transgenic line in which the molecular clock is selectively blocked in the melatonin-producing cells of the pineal gland by a dominant-negative strategy. As a result, clock-controlled rhythms of melatonin production in the adult pineal gland were disrupted. Moreover, transcriptome analysis revealed that the circadian expression pattern of the majority of clock-controlled genes in the adult pineal gland is abolished. Importantly, circadian rhythms of behavior in zebrafish larvae were affected: rhythms of place preference under constant darkness were eliminated, and rhythms of locomotor activity under constant dark and constant dim light conditions were markedly attenuated. On the other hand, global peripheral molecular oscillators, as measured in whole larvae, were unaffected in this model. In conclusion, characterization of this novel transgenic model provides evidence that the molecular clock in the melatonin-producing cells of the pineal gland plays a key role, possibly as part of a multiple pacemaker system, in modulating circadian rhythms of behavior.

CIGESMED for divers: Establishing a citizen science initiative for the mapping and monitoring of coralligenous assemblages in the Mediterranean Sea.

BackgroundOver the last decade, inventorying and monitoring of marine biodiversity has significantly benefited from the active engagement of volunteers. Although several Citizen Science projects concern tropical reef ecosystems worldwide, none of the existing initiatives has yet specifically focused on their Mediterranean equivalents. Mediterranean coralline reefs, known as “coralligenous”, are bioherms primarily built by calcifying rhodophytes on hard substrates under dim-light conditions; they are considered hotspots of biodiversity and are extremely popular among divers due to their complex structure, conspicuous biological wealth and high aesthetic value. Nevertheless, data on their distribution, structure and conservation status is lacking for several Mediterranean areas while they are vulnerable to an increasing number of threats.New informationIn the framework of CIGESMED SeasEra (ERAnet) project a specialized Citizen Science project was launched, aiming to engage enthusiast divers in the study and monitoring of Mediterranean coralligenous assemblages through the gathering of basic information regarding their spatial occurrence, assemblage structure and associated pressures or threats. For its active implementation, a data collection protocol and a multilingual website were developed, comprising an educational module and a data submission platform. Georeferenced data reporting focuses on: (a) basic topographic and abiotic features for the preliminary description of each site, and the creation of data series for sites receiving multiple visits; (b) presence and relative abundance of typical conspicuous species, as well as (c) existence of pressures and imminent threats, for the characterization and assessment of coralligenous assemblages. A variety of tools is provided to facilitate end users, while divers have the choice to report additional information and are encouraged to upload their photographs. The long-term goal is the development of an active community of amateur observers providing widespread and ecologically significant data on coralligenous assemblages.

Involvement of circadian clock in crowing of red jungle fowls (Gallus gallus).

The rhythmic locomotor behavior of flies and mice provides a phenotype for the identification of clock genes, and the underlying molecular mechanism is well studied. However, interestingly, when examining locomotor rhythm in the wild, several key laboratory-based assumptions on circadian behavior are not supported in natural conditions. The rooster crowing 'cock-a-doodle-doo' is a symbol of the break of dawn in many countries. Previously, we used domestic inbred roosters and showed that the timing of roosters' crowing is regulated by the circadian clock under laboratory conditions. However, it is still unknown whether the regulation of crowing by circadian clock is observed under natural conditions. Therefore, here we used red jungle fowls and first confirmed that similar crowing rhythms with domesticated chickens are observed in red jungle fowls under the laboratory conditions. Red jungle fowls show predawn crowing before light onset under 12:12 light : dim light conditions and the free-running rhythm of crowing under total dim light conditions. We next examined the crowing rhythms under semi-wild conditions. Although the crowing of red jungle fowls changed seasonally under semi-wild conditions, predawn crowing was observed before sunrise in all seasons. This evidence suggests that seasonally changed crowing of red jungle fowls is under the control of a circadian clock.

Body size limits dim-light foraging activity in stingless bees (Apidae: Meliponini).

Stingless bees constitute a species-rich tribe of tropical and subtropical eusocial Apidae that act as important pollinators for flowering plants. Many foraging tasks rely on vision, e.g. spatial orientation and detection of food sources and nest entrances. Meliponini workers are usually small, which sets limits on eye morphology and thus quality of vision. Limitations are expected both on acuity, and thus on the ability to detect objects from a distance, as well as on sensitivity, and thus on the foraging time window at dusk and dawn. In this study, we determined light intensity thresholds for flight under dim light conditions in eight stingless bee species in relation to body size in a Neotropical lowland rainforest. Species varied in body size (0.8–1.7 mm thorax-width), and we found a strong negative correlation with light intensity thresholds (0.1–79 lx). Further, we measured eye size, ocelli diameter, ommatidia number, and facet diameter. All parameters significantly correlated with body size. A disproportionately low light intensity threshold in the minute Trigonisca pipioli, together with a large eye parameter Peye suggests specific adaptations to circumvent the optical constraints imposed by the small body size. We discuss the implications of body size in bees on foraging behavior.Electronic supplementary materialThe online version of this article (doi:10.1007/s00359-016-1118-8) contains supplementary material, which is available to authorized users.

Constraint is associated with earlier circadian phase and morningness: Confirmation of relationships between personality and circadian phase using a constant routine protocol

Associations amongst personality, diurnal preference, and circadian phase were investigated using a constant routine laboratory protocol. One hundred and sixty-eight healthy participants aged 18–30years (Women n=68) completed either a 30- or 50-hour constant routine under dim-light conditions (<3lx), during which circadian phase was measured from core body temperature and melatonin. Prior to laboratory admission, self-report measures of personality and diurnal preference were also obtained. The personality trait of Constraint correlated positively with morning diurnal preference and earlier circadian phase, with circadian phase partially mediating the relationship between Constraint and diurnal preference. No other personality variables correlated with circadian phase. Sex was an important covariate in several of the relationships investigated due to lower levels of Constraint and later CBT phase amongst men and was thus controlled for in all relevant analyses. Findings from this highly controlled study are consistent with previous field research in suggesting that earlier circadian phase is associated with the personality trait of Constraint.

Evolution of body size, vision, and biodiversity of coral-associated organisms: evidence from fossil crustaceans in cold-water coral and tropical coral ecosystems.

BackgroundModern cold-water coral and tropical coral environments harbor a highly diverse and ecologically important macrofauna of crustaceans that face elevated extinction risks due to reef decline. The effect of environmental conditions acting on decapod crustaceans comparing these two habitats is poorly understood today and in deep time. Here, we compare the biodiversity, eye socket height as a proxy for eye size, and body size of decapods in fossil cold-water and tropical reefs that formed prior to human disturbance.ResultsWe show that decapod biodiversity is higher in fossil tropical reefs from The Netherlands, Italy, and Spain compared to that of the exceptionally well-preserved Paleocene (Danian) cold-water reef/mound ecosystem from Faxe (Denmark), where decapod diversity is highest in a more heterogeneous, mixed bryozoan-coral habitat instead of in coral and bryozoan-dominated facies. The relatively low diversity at Faxe was not influenced substantially by the preceding Cretaceous/Paleogene extinction event that is not apparent in the standing diversity of decapods in our analyses, or by sampling, preservation, and/or a latitudinal diversity gradient. Instead, the lower availability of food and fewer hiding places for decapods may explain this low diversity. Furthermore, decapods from Faxe are larger than those from tropical waters for half of the comparisons, which may be caused by a lower number of predators, the delayed maturity, and the increased life span of crustaceans in deeper, colder waters. Finally, deep-water specimens of the benthic crab Caloxanthus from Faxe exhibit a larger eye socket size compared to congeneric specimens from tropical reefs, suggesting that dim light conditions favored the evolution of relatively large eyes.ConclusionsThe results suggest a strong habitat control on the biodiversity of crustaceans in coral-associated environments and that the diversity difference between deep, cold-water reefs and tropical reefs evolved at least ~63 million years ago. Futhermore, body size and vision in crustaceans evolved in response to environmental conditions in the deep sea. We highlight the usefulness of ancient reefs to study organismal evolution and ecology.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0694-0) contains supplementary material, which is available to authorized users.

Morning and Evening Blue-Enriched Light Exposure Alters Metabolic Function in Normal Weight Adults

Increasing evidence points to associations between light-dark exposure patterns, feeding behavior, and metabolism. This study aimed to determine the acute effects of 3 hours of morning versus evening blue-enriched light exposure compared to dim light on hunger, metabolic function, and physiological arousal. Nineteen healthy adults completed this 4-day inpatient protocol under dim light conditions (<20lux). Participants were randomized to 3 hours of blue-enriched light exposure on Day 3 starting either 0.5 hours after wake (n = 9; morning group) or 10.5 hours after wake (n = 10; evening group). All participants remained in dim light on Day 2 to serve as their baseline. Subjective hunger and sleepiness scales were collected hourly. Blood was sampled at 30-minute intervals for 4 hours in association with the light exposure period for glucose, insulin, cortisol, leptin, and ghrelin. Homeostatic model assessment of insulin resistance (HOMA-IR) and area under the curve (AUC) for insulin, glucose, HOMA-IR and cortisol were calculated. Comparisons relative to baseline were done using t-tests and repeated measures ANOVAs. In both the morning and evening groups, insulin total area, HOMA-IR, and HOMA-IR AUC were increased and subjective sleepiness was reduced with blue-enriched light compared to dim light. The evening group, but not the morning group, had significantly higher glucose peak value during blue-enriched light exposure compared to dim light. There were no other significant differences between the morning or the evening groups in response to blue-enriched light exposure. Blue-enriched light exposure acutely alters glucose metabolism and sleepiness, however the mechanisms behind this relationship and its impacts on hunger and appetite regulation remain unclear. These results provide further support for a role of environmental light exposure in the regulation of metabolism.

In Situ Hydrogen Dynamics in a Hot Spring Microbial Mat during a Diel Cycle.

Microbes can produce molecular hydrogen (H2) via fermentation, dinitrogen fixation, or direct photolysis, yet the H2 dynamics in cyanobacterial communities has only been explored in a few natural systems and mostly in the laboratory. In this study, we investigated the diel in situ H2 dynamics in a hot spring microbial mat, where various ecotypes of unicellular cyanobacteria (Synechococcus sp.) are the only oxygenic phototrophs. In the evening, H2 accumulated rapidly after the onset of darkness, reaching peak values of up to 30 μmol H2 liter(-1) at about 1-mm depth below the mat surface, slowly decreasing to about 11 μmol H2 liter(-1) just before sunrise. Another pulse of H2 production, reaching a peak concentration of 46 μmol H2 liter(-1), was found in the early morning under dim light conditions too low to induce accumulation of O2 in the mat. The light stimulation of H2 accumulation indicated that nitrogenase activity was an important source of H2 during the morning. This is in accordance with earlier findings of a distinct early morning peak in N2 fixation and expression of Synechococcus nitrogenase genes in mat samples from the same location. Fermentation might have contributed to the formation of H2 during the night, where accumulation of other fermentation products lowered the pH in the mat to less than pH 6 compared to a spring source pH of 8.3. Hydrogen is a key intermediate in anaerobic metabolism, and with the development of a sulfide-insensitive microsensor for H2, it is now possible to study the microdistribution of H2 in stratified microbial communities such as the photosynthetic microbial mat investigated here. The ability to measure H2 profiles within the mat compared to previous measurements of H2 emission gives much more detailed information about the sources and sinks of H2 in such communities, and it was demonstrated that the high rates of H2 formation in the early morning when the mat was exposed to low light intensities might be explained by nitrogen fixation, where H2 is formed as a by-product.

The nature of self-regulation in photosynthetic light-harvesting antenna.

The photosynthetic apparatus of green plants is well known for its extremely high efficiency that allows them to operate under dim light conditions. On the other hand, intense sunlight may result in overexcitation of the light-harvesting antenna and the formation of reactive compounds capable of 'burning out' the whole photosynthetic unit. Non-photochemical quenching is a self-regulatory mechanism utilized by green plants on a molecular level that allows them to safely dissipate the detrimental excess excitation energy as heat. Although it is believed to take place in the plant's major light-harvesting complexes (LHC) II, there is still no consensus regarding its molecular nature. To get more insight into its physical origin, we performed high-resolution time-resolved fluorescence measurements of LHCII trimers and their aggregates across a wide temperature range. Based on simulations of the excitation energy transfer in the LHCII aggregate, we associate the red-emitting state, having fluorescence maximum at ∼700 nm, with the partial mixing of excitonic and chlorophyll-chlorophyll charge transfer states. On the other hand, the quenched state has a totally different nature and is related to the incoherent excitation transfer to the short-lived carotenoid excited states. Our results also show that the required level of photoprotection in vivo can be achieved by a very subtle change in the number of LHCIIs switched to the quenched state.

(Invited) Cost-Effective Anthryl Dyes for Dye-Sensitized Cells Under Dim Light

A series of anthracene-based organic dyes were prepared via cost-effective synthetic procedures for dye-sensitized cell application. UV-visible and fluorescent spectra, electrochemical properties as well as photovoltaic performance of the dyes were studied. Under one sun (100 mW/cm2), the AN-3 small cell (area = 0.16 cm2) outperforms others in the series. Under a dim light condition, the AN-3 modules (area = 36 cm2, manufactured by TDP, Taiwan) showed PCE comparable to that of the Z907 modules. After optimizing the synthetic procedure, we found that AN-3 can be manufactured at a fairly low price. Reference: J. Phys. Chem. C 2015, 119, 24282−24289 Figure 1