Minimum Light Research Articles

Optimized Angular Selective Filtering of Direct Solar Radiation

A method to optimize angular selective filtering of direct solar radiation by minimization of the directional light transmission of a window at preset date and time of day, taking into account the geographical coordinates of building, the trajectory of the sun, the seasonal and daily distribution of radiation intensity, and the azimuth of the window is proposed. The minimum light transmittance is ensured by application of an optical filter with two sloped surface gratings at the expense of optimum slope angle of filter’s gratings on the window pane(s), widths of transmissive and non-transmissive strips of both gratings, and their mutual arrangement. Results of determination of the optimum slope angles of filter’s gratings at the different dates, azimuths of the window, latitudes, refractive indices and distances between filter’s gratings are demonstrated.

Minimum Light Requirements for Indoor Gardening of Lettuce

Indoor food‐gardening is an important trend in horticulture. However, most research‐based light recommendations are oriented towards commercial production, with recommended daily light integrals (DLI) significantly higher than those found inside a home environment. The objective was to evaluate growth (fresh and dry mass), accumulation of key phytochemical constituents (leaf photosynthetic pigment and nitrate content), and aesthetic quality (elongation and pigmentation) of red‐leaf lettuce (Lactuca sativa) grown from transplant to a harvest stage in an indoor environment using different (i) light sources (light‐emitting diode [LED] vs. fluorescent lamps), and (ii) light quantities (from 1.6 to 9.7 mol m−2 d−1). In the first experiment, four broadband white light sources were compared in a growth chamber using 5.2 mol∙m−2∙d−1: (i) ‘neutral‐white’ 4000‐K LED lamps, (ii) ‘day‐white’ 5000‐K LED lamps, (iii) ‘neutral‐white’ 4100‐K fluorescent lamps, or (iv) ‘daylight’ 6500‐K fluorescent lamps. Lettuce grown under LED lamps produced more shoot fresh and dry mass than those grown under fluorescent lamps. However, all light sources resulted in comparable growth and quality attributes. In two separate experiments, plants were grown under one of four DLI. As DLI increased, plants had more growth, higher aesthetic quality (more compact leaves and higher pigment content), and superior nutritional quality (increased leaf concentrations of anthocyanin and carotenoid, and reduced nitrate). Based on these results, a minimum DLI of 6.5 to 9.7 mol m−2 d−1 is recommended when designing indoor gardening systems for red‐leaf lettuce plants.

Novel Light/Dark Regimens with Minimum Light Promote Circadian Disruption: Simulations with a Model Oscillator.

Artificial lab manipulation of LD cycles has enabled simulations of the disruptive conditions found in modern human societies, such as jet-lag, night-work and light at night. New techniques using animal models have been developed, and these can greatly improve our understanding of circadian disruption. Some of these techniques, such as in vivo bioluminescence assays, require minimum external light. This requirement is challenging because the usual lighting protocols applied in circadian desynchronization experiments rely on considerable light input. Here, we present a novel LD regimen that can disrupt circadian rhythms with little light per day, based on computer simulations of a model limit-cycle oscillator. The model predicts that a single light pulse per day has the potential to disturb rhythmicity when pulse times are randomly distributed within an interval. Counterintuitively, the rhythm still preserves an underlying 24-h periodicity when this interval is as large as 14 h, indicating that day/night cues are still detectable. Only when pulses are spread throughout the whole 24-h day does the rhythm lose any day-to-day period correlation. In addition, the model also reveals that stronger pulses of brighter light should exacerbate the disrupting effects. We propose the use of this LD schedule-which would be compatible with the requirements of in vivo bioluminescence assays-to help understand circadian disruption and associated illnesses.

Low light intensity in Pekin duck breeder barns has a greater impact on the fertility of drakes than hens

The Pekin duck is an excellent model for the study of seasonal reproduction. To more completely understand the lighting requirements for maximal fertility in duck breeder houses, we housed adult (45 week old) drakes and hens in the Hope College aviary as 5 drakes and 25 hens. Light conditions in each floor pen were normalized based upon quantal energy and divided into the following categories: (1) to simulate summer, 14.5h 65 lux with 9.5h 1 lux; (2) to simulate winter, 8h 65 lux with 16 h 1 lux; (3) winter augmented, 8h 65 lux with 16 h at 15 lux. The experiment was repeated with rotation of light treatments among 3 pens until a final N = 6 was obtained. Daily, total number of eggs laid was tallied, and a daily average of eggs laid was calculated throughout the study. Weekly, eggs were weighed and the perivitilline membrane was assayed for the number of sperm holes as an indirect measure of drake fertility. As expected, winter conditions caused a reduction in the percent of eggs laid and a reduction in the number of fertilized eggs compared to the summer light conditions. The augmented winter light conditions prevented the loss in the percent eggs laid and fertilized eggs. Surprisingly, even after 4 wk of the study, the winter conditions did not cause a complete loss of fertility in the Pekin ducks. At the end of the study, no differences in the relative expression in brain deep brain photoreceptors or gonadotropin inhibitory hormone mRNAs were observed among any light treatment. Although a minimum (1 lux) of light can support some fertility, our findings suggest commercial Pekin duck barns may benefit from increasing the augmented light to 15 lux to maintain optimal fertility during winter months. Furthermore, our data suggest that drakes may be more sensitive to environmental light conditions than hens.

Investigation of optical and dielectric properties of CsPbI3 inorganic lead iodide perovskite thin film

Abstract This experimental work reports refractive index, extinction coefficients, and dielectric functions at different incident angles in visible range for the first time. The refractive index of CsPbI3 thin film is 2.46 at 435 nm with this result implies that Cs based lead halide solar cells may be, ideal antireflection coating for many tandem solar cells. Thus lower refractive index of CsPbI3 inorganic perovskite material is beneficial for perovskite device fabrications because of the minimum light looses to reflection at the front of the active layer. Furthermore microstructure of the cubic phase Pm-3 m was investigated by X-ray diffraction. CsPbI3 perovskite thin film showed the sharp absorption edge and PL emission near infrared region with direct band gap of 1.67 eV with high color purity of red emission. In addition, the higher dielectric function value of CsPbI3, will helps to many optoelectronic devices.

Improvement of salt gradient solar ponds’ performance using nanoparticles inside the storage layer

The solar pond is one of the usual tools used for solar energy harvesting in the world, although its low efficiency is still a big challenge. In this study, to enhance the thermal efficiency of the laboratory-scale salinity gradient solar pond, three different nanoparticles, i.e., SiO2, Fe3O4, and ZnO, were dispersed into a salt-water solution as the based liquid. Nanoparticles’ mass concentrations used in the based liquid were 0.012%, 0.036%, and 0.06%. The simulated sunlight thermal energy was supplied by a 500 W halogen lamp. The prepared nanofluids were used as lower layer of the pond. Approximately 3 days after filling the pond, the stable salinity gradient was formed and after almost 2 days of exposure to the simulated sunlight, the temperature of the pond layers reached thermal equilibrium. The results showed that lower layer temperature increased continuously with nanoparticles’ concentration, for all nanofluids. Based on the measured temperature, the pond thermal performance was calculated, showing that all mentioned nanoparticles could enhance the thermal efficiency of the SGSP. The maximum lower layer temperature (~ 47 °C) and thermal efficiency enhancement ratio (35.13%) were obtained for the 0.06% ZnO nanofluid. This nanofluid showed the minimum light scattering (particle size parameter = 0.248) and transmittance (near zero) over the UV–Vis wavelength, leading to the increased thermal efficiency of the pond, as compared to the SiO2 and Fe3O4 nanofluids. In addition, using nanoparticles, the time required to reach equilibrium conditions in the pond was decreased, with the maximum of about 9 h.

TY Pup: A Low-mass-ratio and Deep Contact Binary as a Progenitor Candidate of Luminous Red Novae

Abstract TY Pup is a well-known bright eclipsing binary with an orbital period of 0.8192 days. New light curves in B, V, (RI) C bands were obtained with the 0.61 m reflector robotic telescope (PROMPT-8) at CTIO in Chile during 2015 and 2017. By analyzing those photometric data with the W–D method, it is found that TY Pup is a low-mass-ratio (q ∼ 0.184) and deep-contact binary with a high fill-out factor (84.3%). An investigation of all available times of minimum light including three new ones obtained with the 60 cm and the 1.0 m telescopes at Yunnan Observatories in China indicates that the period change of TY Pup is complex. An upward parabolic variation in the O − C diagram is detected to be superimposed on a cyclic oscillation. The upward parabolic change reveals a long-term continuous increase in the orbital period at a rate of dP/dt = 5.57(±0.08) × 10−8 days yr−1. The period increase can be explained by mass transfer from the less massive component (M 2 ∼ 0.3 M ⊙) to the more massive one (M 1 ∼ 1.65 M ⊙). The binary will be merging when it meets the criterion that the orbital angular momentum is less than three times the total spin angular momentum, i.e., J orb < 3J rot. This suggests that the system will finally merge into a rapid-rotating single star and may produce a luminous red nova. The cyclic oscillation in the O − C diagram can be interpreted by the light-travel time effect via the presence of a third body.

Wind and nebula of the M 33 variable GR 290 (WR/LBV)

Context. GR 290 (M 33/V532 = Romano’s Star) is a suspected post-luminous blue variable star located in M 33 galaxy that shows a rare Wolf–Rayet (WR) spectrum during its minimum light phase. In spite of many studies, its atmospheric structure, its circumstellar environment, and its place in the general context of massive stars’ evolution is poorly known. Aims. We present a detailed study of this star’s wind and mass loss, and a study of the circumstellar environment associated to the star. Methods. Long-slit spectra of GR 290 were obtained during its present minimum luminosity phase with the Gran Telescopio Canarias covering the ∼3600–7500 Å wavelength range together with contemporaneous photometry using B, V, R and I filters. The data were compared with non-local thermodynamical equilibrium (non-LTE) model atmosphere synthetic spectra computed with CMFGEN code and with models for ionized interstellar medium regions computed with CLOUDY code. Results. The current mV = 18.8 mag is the faintest at which this source has ever been observed. The non-LTE models indicate effective temperatures of Teff = 27 000–30 000 K at radius R2/3 = 27−21 R⊙ and mass-loss rate Ṁ = 1.5 × 10−5 M⊙yr−1. The terminal wind speed v∞ = 620 km s−1 is faster than ever before recorded, while the current luminosity L* = (3.1–3.7) × 105L⊙ is the lowest ever deduced. The star is overabundant in He and N and underabundant in C and O. It is surrounded by an unresolved compact H II region with dimensions ≤4 pc, from where H-Balmer, He I lines, and [O III] and [N II] are detected. In addition, we find emission from a more extended interstellar medium (ISM) region, which appears to be asymmetric, with a larger extent to the east (16–40 pc) than to the west. Conclusions. In the present long lasting visual minimum, GR 290 is in a lower bolometric luminosity state with higher mass-loss rate. The nearby nebular emission seems to suggest that the star has undergone significant mass loss over the past 104–105 yr and is nearing the end stages of its evolution.

On the variation of light-curve parameters of RR Lyrae variables at multiple wavelengths

We present a detailed light-curve analysis of RR Lyrae variables at multiple wavelengths using Fourier decomposition method. The time-series data for RR Lyrae variables in the Galactic bulge and the Magellanic Clouds are taken from the Optical Gravitational Lensing Experiment survey while the infrared light curves are compiled from the literature. We also analyse the multiband theoretical light curves that are generated from the stellar pulsation models of RR Lyrae stars for a wide range of metal abundances. We find that the theoretical light-curve parameters with different metal abundances are consistent with observed parameters in most period bins at both optical and infrared wavelengths. The theoretical and observed Fourier amplitude parameters decrease with increase in wavelength while the Fourier phase parameters increase with wavelength at a given period. We use absolute magnitudes for a subset of theoretical models that fit the observed optical RR Lyrae light curves in the Large Magellanic Cloud to estimate a distance modulus, μLMC = 18.51 ± 0.07, independent of the metallicity. We also use Fourier analysis to study the period–colour and amplitude–colour relations for RR Lyrae stars in the Magellanic Clouds using optical data and find that the slope of period–colour relation at minimum light is very shallow or flat and becomes increasingly significant at the maximum light for RRab stars. We also find that the metallicity dependence of the period–colour relations increases as we go from minimum to maximum light, suggesting that the mean light results are indeed an average of the various pulsational phases. We summarize that the average variation in these relations is consistent between theory and observations and supports the theory of the interaction of the stellar photosphere and the hydrogen ionization front.

Fast spectrophotometry of WD 1145+017

WD 1145+017 is currently the only white dwarf known to exhibit periodic transits of planetary debris as well as absorption lines from circumstellar gas. We present the first simultaneous fast optical spectrophotometry and broad-band photometry of the system, obtained with the Gran Telescopio Canarias (GTC) and the Liverpool Telescope (LT), respectively. The observations spanned $5.5$ h, somewhat longer than the $4.5$-h orbital period of the debris. Dividing the GTC spectrophotometry into five wavelength bands reveals no significant colour differences, confirming grey transits in the optical. We argue that absorption by an optically thick structure is a plausible alternative explanation for the achromatic nature of the transits that can allow the presence of small-sized ($\sim\mu$m) particles. The longest ($87$ min) and deepest ($50$ per cent attenuation) transit recorded in our data exhibits a complex structure around minimum light that can be well modelled by multiple overlapping dust clouds. The strongest circumstellar absorption line, Fe II $\lambda$5169, significantly weakens during this transit, with its equivalent width reducing from a mean out-of-transit value of $2$ \AA\ to $1$ \AA\ in-transit, supporting spatial correlation between the circumstellar gas and dust. Finally, we made use of the Gaia Data Release 2 and archival photometry to determine the white dwarf parameters. Adopting a helium-dominated atmosphere containing traces of hydrogen and metals, and a reddening $E(B-V)=0.01$ we find $T_\mathrm{eff}=15\,020 \pm 520$ K, $\log g=8.07\pm0.07$, corresponding to $M_\mathrm{WD}=0.63\pm0.05\ \mbox{$\mathrm{M}_{\odot}$}$ and a cooling age of $224\pm30$ Myr.

Orbital period changes of the W UMa binary YY Eri

Orbital period changes of the W UMa-type binary YY Eri are analyzed by using all photoelectric and ccd times of light minimum. The results show that its orbital period is undergoing a secular increase superposed on two cyclic oscillations. The continuous increase at the rate of may be accounted for by mass transfer from the less massive companion to the more massive one. Two periodic variations with periods of 38.6192 and 22.3573 yr may be attributed to the light-time effect of a faint third star and the cyclic magnetic activity of the system, respectively.

Graphene–MoS2–metal hybrid structures for plasmonic biosensors

Abstract Surface Plasmon Resonance (SPR) biosensors are widely used for real-time label-free detection in medical diagnostics, pharmaceutical researches and food safety. Although there is a growing interest in miniaturization of biosensors for self-detection and diagnostics at out of laboratory, the performance of conventional metal SPR sensors is still limited. In this paper, we propose graphene–MoS 2 – metal hybrid structures based plasmon sensors under the best minimum light intensity approach, which represents the performance analysis in case of the lowest reflected light strength. It is demonstrated that the metal thickness can be reduced from 55 nm to 32 nm and 37 nm meanwhile the performance of the background sensor can be improved by 87% and 13% with the 4 additional MoS2 and graphene layers, respectively. We show that MoS2 based SPR devices provide much better sensitivity performance than graphene based devices. Our results reveal the another promising property of MoS2: The sensitivity of SPR sensors can be greatly increased with a few number of MoS2 within the angular SPR system while reducing the size of the device, especially for particular applications such as detecting a single molecule and biosensing at low biomolecule concentration. Furthermore, we show that the equivalent optical properties of multilayered nanostructures also depend on the layer thickness which is a novel knowledge for the next studies on 2D material based SPR plasmonic devices.

A Peculiar Interacting Be Star Binary in the Small Magellanic Cloud**Based on the ESO proposal 098.D-0099(A).

We find that the emission-line object OGLEJ005039.05-725751.4, a member of the cluster OGLE-CL SMC 64, exhibits a peculiar light curve pattern repeating with a recurrence time of 141.45 days. The light curve resembles periodic outbursts with a duty cycle of 20%. A second long cycle of 2500 days is also detected in the photometric data set. Two X-SHOOTER spectra obtained at minimum and maximum reveal a Be star dominating at minimum light resembling the Classical Be star 48 Lib. The larger Hα emission, the stronger Na D absorption and the appearance of emission in the infrared Ca II triplet at maximum, might indicate periodic mass transfer in a complex binary system.

RZ Pyx: A Special Short Period Detached Massive Binary with Two Cool Stellar Companions in a Quadruple System

RZ Pyx is one of a small group of short-period B-type eclipsing binaries with an orbital period of 0.656 days. Several new CCD times of light minimum of RZ Pyx were obtained. Together with all available photoelectric and CCD times of light minimum, the changes of the orbital period are investigated for the first time. Meanwhile, previously published light curves are reanalyzed with the Wilson–Devinney code. Based on the analysis of the O–C diagram, two cyclic variations with periods of 37.1 years and 9.7 years are discovered superimposed on a continuous increase at a rate of dP/dt = +0.32 × 10−7 day yr−1. The light curve solutions suggest that RZ Pyx is a marginal detached binary system where both components do not overfill their respective Roche lobes. The fill-out factors of the primary and the secondary component are 95.5(±0.8)% and 99.1(±1.9)%, respectively, revealing that the secondary is nearly filling its Roche lobe. This may indicate that RZ Pyx has undergone a mass-transferring evolutionary stage and it is on the marginal detached stage temporarily. The long-term increase in the orbital period could be explained by the enhanced mass loss by stellar winds of the two detached massive components. Since the two binary components are early-type stars, the two cyclic oscillations could be plausibly interpreted as the results of the light travel-time effect caused by the presence of two additional companions. It is estimated that the masses of the two additional bodies are no less than 0.36 M⊙ and 0.21 M⊙, respectively. The two cool stellar companions are orbiting the central binary at orbital separations of 23.1 and 9.5 au in a quadruple stellar system. Both the marginal detached configuration and the presence of two cool stellar companions make RZ Pyx a very interesting binary system for further investigations.

Changes in ocular surface status after phacoemulsification in patients with senile cataract

To evaluate the signs and symptoms of dry eye after phacoemulsification; effects on the status of ocular surface using impression cytology; and associated risk factors. Prospective study included 50 eyes (50 patients) with no dry eye signs or symptoms, who underwent clear corneal phacoemulsification for senile cataract. Dry eye indices used included Ocular Surface Disease Index scoring, Schirmer I test, tear break up time, tear meniscus height, corneal fluorescein staining, lissamine green staining and goblet cell density (GCD) with the help of impression cytology. Primary outcome measures included post-operative changes in the dry eye indices. Secondary outcome measures included correlation of the dry eye signs and symptoms with various risk factors. Aggravation of both the signs and symptoms of dry eye were noted in immediate post-operative period. The sharp deterioration was followed by a recovering trend towards the end of sixth week. A decrease in GCD was also noted. Risk factors for deterioration include age, duration of exposure to microscope light and effective phacoemulsification time. Diabetic status, socio-economic status and site of incision did not have any effect on dry eye status. There is a transient deterioration of "dry eye" status post-phacoemulsification. The patients should be carefully counselled about the evanescent nature of the disease. Incision can be given at the site of high corneal curvature to neutralize astigmatism without any fear of inducing dry eye. Minimum light exposure and ultrasound energy should be used during the surgery.

First CCD photometric investigation of the eclipsing binary V737 Per

New CCD photometric observations of the eclipsing binary V737 Per have been performed in 2015 and complete BV bands light curves are obtained. From the observations, four times of light minimum are determined. By combining these times of light minimum with those collected from literature, we derive a new linear ephemeris and investigate the orbital period variation. The result shows that no significant period variation can be found during the past twelve years. The present light curves are analyzed by using the Wilson–Devinney code. The photometric solutions indicate that the system is an A-type, shallow-contact binary with a mass ratio of 0.41 and a degree of contact of 8.73%. Also, the asymmetry of the light curves is observed. It can be explained by a cool spot on the secondary component. Finally, we estimate the absolute parameters of V737 Per and discuss its evolutionary status. The results suggest that the primary of V737 Per has evolved away from the zero age main sequence.

Light Stress Responses by the Eelgrass, Zostera marina (L)

Zostera marina is the dominant seagrass species in the Northern Hemisphere where it grows in sheltered bays and estuaries. As a consequence of its distribution its conservation is commonly threatened by poor coastal water quality. The high minimum light requirements of seagrasses results in water quality degradation (high turbidity and eutrophication) being a significant risk. Bioindicators of light stress can be used to interpret seagrass responses to light limitation and therefore act as sentinels for conservation management. However, there exists limited experimental inter-comparison of the effectiveness of multiple individual bioindicator responses. Meta-analysis suggests that rhizome sugars, shoot C:N, shoot growth and number of leaves per shoot provide the most consistent response variables to increasing light limitation in seagrass, but this premise remains largely untested at the plant level as a direct comparison of multiple bioindicators. The present study aimed to test the morphological, physiological and photo-physiological bioindicator responses of Z. marina to light stress applied within controlled laboratory conditions. These bioindicators were used to assign minimum light thresholds. Growth rate and photophysiological parameters (alpha, Ek and ETRmax) were rapidly (1st week) and drastically affected by low light shade treatments (20.12 µmol photons m-2s-1 and lower). After three weeks at low light, significant reductions in maximum leaf length and leaf width were observed. Principal Component Analysis identified leaf length, shoot growth, shoot surface area, ETRmax, Ek and alpha as having the strongest responses to reduced light. Shoot growth, ETRmax, Ek and alpha were found to provide the best early warning of light limitation after 5-8 days. These results provide evidence for bioindicators of light stress in Z. marina and highlights the importance of understanding these responses for the successful management and conservation of this species.

Organic tandem solar cells: How impedance analyses can improve the quality of external quantum efficiency measurements

AbstractTandem architectures are one of the most promising concepts towards superior power conversion efficiencies of organic solar cells. An accurate determination of the power conversion efficiency requires correction of the spectral mismatch and thus relies on accurate external quantum efficiency (EQE) spectra. Due to the series connection of 2 subcells in the tandem architecture, the EQE of the tandem solar cell reproduces the EQE of one subcell if an appropriate bias light is chosen to selectively illuminate and hence forward bias the other subcell. The resulting internal voltage drop is then compensated by applying an external voltage to the tandem solar cell. In this work, we use impedance spectroscopy to accurately predict the minimum bias light intensity and the external voltage to enable accurate EQE measurements on both subcells. We exemplify this procedure on organic tandem solar cells comprising spectrally complementary absorbers and suggest an extended protocol for future measurements of the EQE.

Photometric Study of Two Totally Eclipsing Contact Binaries: V789 Her and V1007 Cas

Two sets of V and Rc light curves of V789 Her and one complete set of BVRcIc light curves of V1007 Cas were observed and presented. By analyzing all these light curves together with the Sloan g′i′ light curves observed by Kjurkchieva et al., we determined that both systems are W-subtype contact binaries and that V789 Her is a medium contact system, while V1007 Cas is a shallow contact system. Because the two binaries show totally eclipsing primary minima, the photometric results are reliable. In addition, the light curves of the two systems are asymmetric, requiring a dark spot on the primary or the secondary component in the modeling. By compiling all available times of minimum light including literatures, SuperWASP archive and ours, we analyzed the orbital period variations. We derived that the O − C diagram of V789 Her displays a periodic oscillation whose period and amplitude are 29.2 years and 0.0179 days and the period of V1007 Cas exhibits a continuous decrease at dP/dt = −1.78(±0.09) × 10−7 days yr−1. The cyclic period modulation of V789 Her is probably attributed to the light travel time effect via a tertiary companion with very small mass. The continuous period decrease of V1007 Cas may result from the mass transfer between the two components. However, we cannot rule out the possibility of angular momentum loss because V1007 Cas shows strong magnetic activity. By analyzing the evolutionary status of the components of the two systems, we determined that they exhibit typical characteristics of other W-subtype contact binaries.

A Study of Light Level Effect on the Accuracy of Image Processing-based Tomato Grading

Image processing method has been used in non-destructive tests of agricultural products. Compared to manual method, image processing method may produce more objective and consistent results. Image capturing box installed in currently used tomato grading machine (TEP-4) is equipped with four fluorescence lamps to illuminate the processed tomatoes. Since the performance of any lamp will decrease if its service time has exceeded its lifetime, it is predicted that this will affect tomato classification. The objective of this study was to determine the minimum light levels which affect classification accuracy. This study was conducted by varying light level from minimum and maximum on tomatoes in image capturing boxes and then investigates its effects on image characteristics. Research results showed that light intensity affects two variables which are important for classification, for example, area and color of captured image. Image processing program was able to determine correctly the weight and classification of tomatoes when light level was 30 lx to 140 lx.