Conditions Of Constant Illumination Research Articles

Electrochemical Regulation of the Cyanobacterial Circadian Oscillation

There has been a growing awareness of a close relationship between circadian oscillation and intracellular redox state in diverse species ranging from cyanobacteria to mammals [1]. The elucidation of this relationship is of physiological importance since malfunction and disruption of the circadian clock can threaten the wellbeing of living organisms. Here we report that the circadian oscillation of the cyanobacterium Synechococcus elongatus PCC7942, the simplest organism found to exhibit circadian oscillation,can be entrained by periodical modulation of the intracellular redox state via electrochemically controlled-extracellular electron transfer (EC-EET), a process in which intracellular electrons are exchanged with extracellular electrodes [2].In-vivo monitoring of chlorophyll fluorescence revealed that the redox state of plastoquionone pool could be controlled by EC-EET with simply changing the electrode potential in the presence of biocompatible electron mediators. As a result, the endogenous circadian clock of S. elongatuscells was successfully entrained through periodically modulated EC-EET by emulating the natural light-and-dark cycle, even under constant illumination conditions. This represents the first example of regulating the biological oscillation via intracellular redox state by electrochemical technique.[1] S. Edgar et al., PNAS10.1073. (2012).[2] Y. Lu et al., Angew. Chem. Int. Ed., 53, 2208-2211 (2014).

Simulation of Multitemporal and Hyperspectral Vegetation Canopy Bidirectional Reflectance Using Detailed Virtual 3-D Canopy Models

The influence of plant and canopy architecture on canopy bidirectional reflectance and the bidirectional reflectance distribution function (BRDF) is the subject of this paper. To understand BRDF-influenced reflectance signals, this influence must be identified and quantified, which requires detailed knowledge concerning the structure and BRDF of the observed canopies. In situ BRDF measurements of canopies are time consuming and depend on the availability of a field goniometer. In contrast to field measurements, computer-based simulations of the canopy BRDF offer an alternative approach that considers parameter-driven setups of virtual canopies under constant illumination conditions. This paper presents the hyperspectral simulation of canopy reflectance (HySimCaR) system, which has been developed in the context of the EnMAP mission. This spectral, spatial, and temporal simulation system consists of detailed virtual 3-D cereal canopies of different phenological stages, whose geometries are linked to the corresponding spectral information. The system enables the simulation of realistic bidirectional reflectance spectra on the basis of virtual 3-D scenarios by incorporating any possible viewing position with ray-tracing techniques. The parameterization of a number of canopy structure parameters, such as phenological stage, row distance, and row orientation, enables the modeling of the bidirectional reflectance and, based on them, the approximation of the BRDF for many structurally different cereal canopies. HySimCaR has been validated with respect to structural and spectral accuracy using three cereal types, namely, wheat, rye, and barley, at 13 different phenological stages. The results show that the virtual cereal canopies are re-created in a realistic way, and it is possible to model their detailed canopy bidirectional reflectance and their BRDF using HySimCaR.

Regulation of the Cyanobacterial Circadian Clock by Electrochemically Controlled Extracellular Electron Transfer

AbstractThere is growing awareness that circadian clocks are closely related to the intracellular redox state across a range of species. As the redox state is determined by the exchange of the redox species, electrochemically controlled extracellular electron transfer (EC‐EET), a process in which intracellular electrons are exchanged with extracellular electrodes, is a promising approach for the external regulation of circadian clocks. Herein, we discuss whether the circadian clock can be regulated by EC‐EET using the cyanobacterium Synechococcus elongatus PCC7942 as a model system. In vivo monitoring of chlorophyll fluorescence revealed that the redox state of the plastoquionone pool could be controlled with EC‐EET by simply changing the electrode potential. As a result, the endogenous circadian clock of S. elongatus cells was successfully entrained through periodically modulated EC‐EET by emulating the natural light/dark cycle, even under constant illumination conditions. This is the first example of regulating the biological clock by electrochemistry.

백색광 LED를 사용한 독서등의 최적 색온도에 따른 사람의 시력 변화 연구

White light emitting diode (LED) determined the most appropriate color temperature in reading lighting evaluated fatigue degree of eye according to color temperature. The eye fatigue degrees are determined by brightness and color temperature. Therefore, we measured the results of eyes test according to the change of color temperature and brightness. Experiments except for astigmatic corrected visual acuity of 0.8 more and age 20 to 25 years old, male and female college students was conducted in 100 patients. And constant illumination conditions, visual acuity was measured by varying the color temperature. The optometry at 10 minutes in the darkroom adapted eye. And then the temperature of <TEX>$25{\pm}3$</TEX> degrees, the humidity was carried out at <TEX>$50{\pm}5%$</TEX>. As a result of typical color temperature of white light (5,600 K) has identification of the readability.

O valor biológico do período circadiano

Experimental protocols that aim to measure the circadian period in humans and other species usually imply the use of artificial, constant conditions of illumination. Since these conditions do not occur naturally, we argue the meaning of measuring the circadian period. Its determination in a situation out of the social context may lead to a more static understanding of biological processes. Finally, the traditional view of the intrinsic circadian period is contrasted in this essay with its possible relation with the current status of the temporization system

Comparative studies of photochemical cross-linking methods for stabilizing the bulk hetero-junction morphology in polymer solar cells

We are here presenting a comparative study between four different types of functionalities for cross-linking. With relatively simple means bromine, azide, vinyl and oxetane could be incorporated into the side chains of the low band-gap polymer TQ1. Cross-linking of the polymers was achieved by UV-light illumination to give solvent resistant films and reduced phase separation and growth of PCBM crystallites in polymer:PCBM films. The stability of solar cells based on the cross-linked polymers was tested under various conditions. This study showed that cross-linking can improve morphological stability but that it has little influence on the photochemical stability which is also decisive for stable device operation under constant illumination conditions.

Automated optical inspection system for digital TV sets

This article proposes a real-time test and verification system for full-reference automatic image quality assessment and verification of digital TV sets. Digital camera is used for acquisition of the TV screen content in order to ensure quality assessment of the content as perceived by the user. Test has been executed in three steps: image acquisition by camera, TV screen content extraction and full-reference image quality assessment. The TV screen content is extracted from the captured image in two steps: detection of the TV screen edge and transformation of the TV screen content to dimensions of the reference image. Three image comparison methods are incorporated to perform full-reference image quality assessment. Reference image for quality assessment is obtained either by grabbing the image from TV set or by capturing the TV screen content on the golden sample. Digital camera was later replaced with DSP-based camera for image acquisition and algorithm execution which brought significant performance improvements. The comparison methods were tested under constant and variable illumination conditions. The proposed system is used to automate the verification step on the final production line of digital TV sets. The time required for verification step decreased by a factor of 5 when using the proposed system on the final production line instead of a manual one.

High response deep ultraviolet organic photodetector with spectrum peak focused on 280 nm

A high response organic deep ultraviolet (DUV) photodetector (PD) with 280 nm as the response spectrum peak was demonstrated. A maximum photoresponse of 309 mA/W under 280 nm UV illumination with an intensity of 0.428 mW/cm2 and a detectivity of 1×1012 cmHz1/2/W at −8 V were achieved, respectively. The optimized PD diode has a structure of ITO/m-MTDATA (10 nm)/m-MTDATA:Bphen(1:1, 60 nm)/Bphen (10 nm)/Cs2CO3: Bphen (30 wt %,10 nm)/Al(12 nm)/TPD(40 nm). Under 280 nm constant and shuttered illumination conditions with an intensity of 0.18 mW/cm2 the operational time is longer than 440 min when its response respectively decreases to 50% and 83% of its original value. The realization of the DUV detection is attributed to the stronger absorption of shorter UV wavelengths of Bphen acceptor and covering UV waveband longer than 300 nm by the TPD layer. The more detailed mechanism of harvesting the high PD performance is also discussed.

Detection of Sympathetic Activation through Measurement and Adaptive Processing of the Pupil Diameter for Affective Assessment of Computer Users

Future human-computer interactions could be enhanced by enabling the computer to detect the user‟s emotional states (e.g. stress), and adjust its interaction behavior appropriately. However, providing the computer with the ability to detect important changes in the user‟s affective state is a challenging problem. We propose that increases in sympathetic activation which typically accompany the onset of stress could be detected noninvasively by monitoring and processing of the pupil diameter (PD) in the computer user. Our previous work indicated that, under constant illumination conditions, there are measurable increases of the pupil diameter in response to stress stimuli, which we have termed the Pupillary Affective Response (PAR). On the other hand, it is known that the Pupillary Light Reflex (PLR) plays a significant role in modifying the pupil diameter and, therefore, the PAR must be separated from the PLR to be useful towards affective assessment of a computer user in environments with variable illumination. To that end, this study adds the measurement of illumination (IL) in the neighborhood of the subject‟s eyes and applies it to the processing of the PD signal through an Adaptive Interference Canceller (AIC) using the H ∞ time-varying (HITV) adaptive algorithm, to remove the influence of the PLR from the pupil diameter variations originally measured. The output of the AIC, the Modified Pupil Diameter (MPD) signal, is subjected to additional processing, to result in a detection feature that is compared against a threshold to obtain an indication of subject “stress”. The performance of this stress detector, along with 9 others derived from Galvanic Skin Response (GSR) and Blood Volume Pulse (BVP) signals is studied through their Receiver Operating Characteristic (ROC) curves.

Single molecule studies of quantum dot fluorescence intermittency: evidence for both dark and light-assisted blinking dynamics

The present work investigates single CdSe QD blinking behaviour in the absence of illumination, in order to elucidate the role of photoexcitation on the long time dynamics. The probability of a QD transitioning in the dark from a high quantum yield (‘on’) state to a low quantum yield (‘off’) state is found to be extremely low and essentially independent of dwell time from <100 ms to minute time scales. The absence of a dark pathway is consistent with many models, for example, in which ‘on’ to ‘off’ blinking is ascribed to photo-assisted Auger ionization and charging of the QD. On the other hand, blinking recovery statistics (from ‘off’ to ‘on’ state) reveal an approximate power law dependence on dwell time, consistent with non-photoactivated and highly distributed kinetics in the dark. Most importantly, such dark QD recovery is orders of magnitude slower than predicted by previous power law kinetic studies under constant illumination conditions, highlighting the presence of both (i) light-activated and (ii) dark blinking recovery pathways. Furthermore, the kinetic analysis indicates that nearly all single CdSe QD studies to date have been performed under conditions where blinking recovery is dominated by the light-activated channel to date.

Exhaled Air and Aerosolized Droplet Dispersion During Application of a Jet Nebulizer

BackgroundAs part of our influenza pandemic preparedness, we studied the dispersion distances of exhaled air and aerosolized droplets during application of a jet nebulizer to a human patient simulator (HPS) programmed at normal lung condition and different severities of lung injury.MethodsThe experiments were conducted in a hospital isolation room with a pressure of − 5 Pa. Airflow was marked with intrapulmonary smoke. The jet nebulizer was driven by air at a constant flow rate of 6 L/min, with the mask reservoir filled with sterile water and attached to the HPS via a nebulizer mask. The exhaled leakage jet plume was revealed by a laser light sheet and images captured by high-definition video. Smoke concentration in the plume was estimated from the light scattered by smoke and droplet particles.FindingsThe maximum dispersion distance of smoke particles through the nebulizer side vent was 0.45 m lateral to the HPS at normal lung condition (oxygen consumption, 200 mL/min; lung compliance, 70 mL/cm H2O), but it increased to 0.54 m in mild lung injury (oxygen consumption, 300 mL/min; lung compliance, 35 mL/cm H2O), and beyond 0.8 m in severe lung injury (oxygen consumption, 500 mL/min; lung compliance, 10 mL/cm H2O). More extensive leakage through the side vents of the nebulizer mask was noted with more severe lung injury.InterpretationHealth-care workers should take extra protective precaution within at least 0.8 m from patients with febrile respiratory illness of unknown etiology receiving treatment via a jet nebulizer even in an isolation room with negative pressure.

Development of the energy flow in light-harvesting dendrimers

Modeling the multistep flow of energy in light-harvesting dendrimers presents a considerable challenge. Recent studies have introduced an operator approach based on a matrix representation of the connectivity between constituent chromophores. Following a review of the theory, detailed applications are now shown to exhibit the time development of the core excitation following pulsed laser irradiation and the steady-state behavior that can be expected under conditions of constant illumination. It is also shown how energy capture by whole dendrimers can be analytically related to chromophore pair-transfer properties and, in particular, the spectroscopic gradient toward the core. Indicative calculations also illustrate the consequences of tertiary folding. In each respect, the model affords opportunities to derive new, physically meaningful information on the photophysical and structural features of dendrimeric systems.

Daily rhythm of aggregation in the haematophagous bug Triatoma infestans (Heteroptera: Reduviidae)

Triatomine bugs show a temporal modulation of many activities. Here, we analyse the daily modulation of the aggregation behaviour of Triatoma infestans larvae and its chronobiological basis. In the laboratory, groups of six bugs were released over an experimental arena during six consecutive days, where their aggregation behaviour was quantified every hour. When submitted to a 12/12 h photoperiod (L/D), the larvae of T. infestans exhibited a cyclic pattern of aggregation with a 24 h period, evincing the existence of a daily rhythm of aggregation in this species. Bugs exhibited the maximum aggregation tendency at the end of the scotophase (7:00 h), moment in which they naturally search for refuges. The minimum aggregation (i.e. maximal dispersion) was observed during the last part of the photophase and beginning of the scotophase (15:00 to 1:00 h). This cyclic pattern disappeared when constant conditions of illumination (L/L) or darkness (D/D) were imposed to the bugs, suggesting the absence of an endogenous circadian control of this behaviour. Insects submitted to L/L and D/D photoperiods presented lower global levels of aggregation than those submitted to L/D conditions. The lack of an endogenous control and the relevance of light cycles as a synchronization signal are discussed as the temporal modulation of this behaviour might play an important role in the nocturnal habits of this species.

Surface states and persistent photocurrent in a GaN heterostructure field effect transistor

AlGaN/GaN heterostructure field effect transistors subject to UV illumination exhibit persistent photoconductivity both in the gate leakage and in the drain current. Time decay modelling of the gate photocurrent enables us to extract the surface potential transient. Simultaneous measurements of drain and gate currents indicate that (i) the gate leakage current negatively charges surface states, (ii) the large change in surface potential induced by UV illumination is responsible for the change in drain current in these devices. We present a detailed analytical model describing the gate and drain current decay transients, following UV illumination, in terms of surface potential modulation due to charging and discharging of surface traps. It is also found that for constant illumination and drain bias voltage conditions the change in the two-dimensional electron gas density is nearly constant independent of the gate bias. Using a previously measured mobility–carrier density relation we determine quantitatively the drain current transient.

Rhythms of glycerophospholipid synthesis in retinal inner nuclear layer cells

The present study demonstrates that the biosynthesis of phospholipids in the inner nuclear layer cells of the chicken retina displays daily rhythms under constant illumination conditions. The vertebrate retina contains circadian oscillators and photoreceptors (PRCs) that temporally regulate its own physiology and synchronize the whole organism to the daily environmental changes. We have previously reported that chicken photoreceptors and retinal ganglion cells (RGCs) present significant daily variations in their phospholipid biosynthesis under constant illumination conditions. Herein, we demonstrate that cell preparations highly enriched in inner nuclear layer cells also exhibit a circadian-regulated phospholipid labeling after the in vivo administration of [ 32P]phosphate or [ 3H]glycerol both in animals maintained under constant darkness or light for at least 48 h. In constant darkness, there was a significant incorporation of both precursors into phospholipids with the highest levels of labeling around midday and dusk. In constant light, the labeling of 32P-phospholipids was also significantly higher during the day and early night whereas the incorporation of [ 3H]glycerol into phospholipids, that indicates de novo biosynthesis, was greater during the day but probably reflecting a higher precursor availability at those phases. We also measured the in vitro activity of phosphatidate phosphohydrolase and diacylglycerol lipase in preparations obtained from the dark condition. The two enzymes exhibited the highest activity levels late in the day. When we assessed the in vitro incorporation of [ 14C]oleate into different lysophospholipids from samples collected at different phases in constant darkness, reaction catalyzed by lysophospholipid acyltransferases II, labeling showed a complex pattern of daily activity. Taken together, these results demonstrate that the biosynthesis of phospholipids in cells of the chicken retinal inner nuclear layer exhibits a daily rhythmicity under constant illumination conditions, which is controlled by a circadian clock.

Daily Increments of Light Hours Near Vernal Equinox Synchronize Circannual Testicular Cycle of Tropical Spotted Munia

In some long-lived organisms, particularly in tropical birds and migrants that spend part of the year close to the equator, endogenous circannual rhythms have been demonstrated in seasonal events like reproduction, molt, and migration. These, like the circadian rhythms, are expressed only in constant conditions of illumination with a periodicity deviating from 1 yr. If birds followed this periodicity, they would soon be out of phase with the annual calendar and perish and, therefore, they would need to be synchronized. However, almost nothing is known as to how synchronization is achieved in birds. Herein, with the help of a suitable model, viz., the tropical spotted munia and long-term experiments conducted in series over a 5-yr period, we provide direct evidence for the first time indicating that the segment of annual photocycle with maximal rate of increase prior to vernal equinox (approximately between mid-February and mid-March) synchronizes the circannual reproductive cycle with the monsoon period of ample food supply through a phase delay. Data also indicate, contrary to the prevalent view, that birds in the tropics can perceive minor changes in day-length, that birds respond to progressive changes in day-length as distinct from responding to fixed photoperiods of particular durations, and that birds can actually distinguish the quality of the environmental signal, viz., vernal equinox from early spring, or increasing days of spring from decreasing days of autumn. The underlying mechanisms, although yet to be identified, appear to involve a gonado-inhibitory rather than the conventional gonado-stimulatory response to increasing day-length. The photoperiodic responses of spotted munia are distinctly different from that of any “long-day” birds described thus far and do not conform to the prevalent “circadian coincidence” hypothesis of photoperiodism.

Is the rhythm of vertical migration of Daphnia longispina circadian or simply nycthemeral ?

From an ecological viewpoint, diel vertical migration (DVM) of zooplankton is an adapted response to environmental factors. DVM coincides with changes in light intensity, but persists also under constant illumination conditions. This fact suggests the existence of an internal clock. In Daphnia longispina, it could be located in the eye. Indeed, the spatial distribution of the pigments containing in the eye ommatidia exhibits significant changes over time when Daphnia are kept under light/dark (LD) conditions. These variations coincide with displacements of the organisms. Furthermore, it is observed that the blue/dark conditions, which inhibit DVM, also stop changes in the distribution of pigments in the ommatidia. The modifications of the eye observed under LD white light represent either the internal clock or its manifestation.

Chronobiological basis of thermopreference in the haematophagous bug Triatoma infestans

The chronobiological basis of the daily dynamics of thermopreference was tested in adults of Triatoma infestans, continuously registering the preferred temperature of insects released over a temperature gradient for 13 days. We found that the thermopreference in T. infestans is a dynamic process that depends on the time of the day and the post-feeding time. When submitted to a 12:12 h light/darkness cycle (L/D), the preferred temperature reached the highest and the lowest values at the end of the light and dark phases, respectively. This daily rhythm persisted under constant conditions of illumination (D/D and L/L), suggesting the existence of an internal oscillator controlling this behaviour. Statistical analysis revealed that the thermopreference of insects kept under L/D exhibited a ca. 24 h periodicity, while insects kept in D/D and L/L showed free-running periods of τ (D/D)=23.35 and τ (L/L)=27.35 h, respectively. The persistence of a cyclic pattern of thermopreference under constant conditions, and free-running periods, close to, but different from 24 h, demonstrate the existence of an endogenous control of the thermopreference in this species. The biological relevance of these results is discussed in the light of the hypothesis that both the length of time elapsed since feeding and the time of the day modify thermopreference in these bugs. The gradual decline in preferred temperature following feeding may be associated with energy conservation during starvation. The rhythmic modulation of thermopreference may be associated with the daily rhythm of locomotion activity shown by these bugs.

Optimizing conditions for growth and sporulation of Pyrenophora semeniperda

The effects of photoperiod, light quality, wounding and sealing of culture plates on in vitro growth and sporulation of Pyrenophora semeniperda were examined to define conditions conducive to the abundant and rapid production of conidia. For maximum growth and sporulation, the leaf‐spotting and seedborne plant pathogen required an alternating light/dark sequence. Fewer conidia were produced under conditions of constant illumination or constant darkness. Growth was enhanced by light of wavelengths longer than 500 nm, while sporulation was enhanced by light of wavelengths shorter than 500 nm. Sporulation was enhanced under conditions of alternating temperature with a diurnal photoperiod and by mycelial wounding. Sealing of Petri plates had an inhibitory effect on sporulation. Significantly more conidia of higher quality formed when unsealed cultures, wounded after 7 days, were exposed to 23°C during the light phase and 19°C during darkness. Under these optimal conditions, conidial numbers were increased by 800% or more compared with unwounded cultures grown at constant 25°C in 12 h alternating cool‐white light.

Effect of Melatonin on the Intensity of Adenosine Production in the Rat Forebrain under Conditions of Acute Hypoxia and Varied Photoperiodicity

We studied the effect of injections of melatonin and modifications of the duration of illumination on the activity of 5′-nucleotidase, an enzyme providing synthesis of adenosine, in the forebrain of juvenile male albino rats. The measurements were performed under conditions of acute hypobaric hypoxia. We found that, under conditions of natural illumination, neither isolated injections of melatonin nor acute hypoxia noticeably changed the activity of 5′-nucleotidase. At the same time, acute hypoxia combined with melatonin injections increased the activity of this enzyme. A similar noticeable rise in the activity of 5′-nucleotidase was observed after melatonin injections in normoxic animals kept in constant darkness, and in rats subjected to hypoxia without the above injections but under conditions of constant illumination. These data allow us to suppose that melatonin (whose level in the extracellular medium is a factor providing synchronization of endogenous temporal rhythms) stimulates 5′-nucleotidase-mediated production of adenosine in brain neurons. Acute hypoxia promotes such an effect of melatonin.