Spectral Distribution Of Light Research Articles

The Fermi-LAT view of the changing-look blazar OQ 334

Context. Unusually, there are still certain characteristics of the changing-look (CL) active galactic nuclei (AGNs) that remain undetected. Consequently, the trigger mechanism behind the CL phenomenon observed in partial AGNs remains unknown. Aims. We explore the light curve and spectral energy distribution (SED) of the CL blazar OQ 334 as obtained by Fermi-LAT. Methods. By examining the variability of the equivalent width (EW), we categorise the Fermi-LAT light curves of OQ 334 during the epoch of MJD 54628−58677 into seven distinct epochs, including the flat spectrum radio quasar (FSRQ) state, the transition state, and the BL Lac state. We obtained both a Fermi-LAT SED and a multi-wavelength SED for each of these distinct epochs. Results. The source exhibits a transformation from a quiescent state to a highly active state, as evidenced by the variability of the EW. The multi-wavelength SEDs display a prominent external Compton characteristic, even though the Fermi-LAT SED reveals both a FSRQ and a BL Lac state across the seven different epochs. To gain further insights, we employed a leptonic model that takes into account the soft photon fields originating from both synchrotron radiation and the external environment. By simulating the multi-wavelength SEDs for each epoch, we uncover the following results. Firstly, the energy density of the external photon fields evolves in an oscillatory manner over the seven different epochs. Also, the energy density of the external photon fields in the BL Lac state is lower than that in the FSRQ state. Conclusions. These findings suggest that the CL blazar represents a unique phase in the blazar sequence. Considering that the energy density of the external photon fields is proportional to the accretion rate, we propose that evidence for the interconversion of advection-dominated accretion flow (ADAF) discs and standard Shakura–Sunyaev discs (SSDs), – as variations in accretion modes in the CL blazar – can be obtained through observations by Fermi-LAT.

Reconsidering the spectral distribution of light: Do people perceive watts or photons?

The spectral distribution is a fundamental property of non-monochromatic optical radiation. It is commonly used in research and practical applications when studying how light interacts with matter and living organisms, including humans. In the field of lighting, misconceptions about the spectral distribution of light are responsible for unfounded claims, which pervade the scientific and technical communities. Starting from the definition of the spectral distribution, this paper describes the ambiguities and errors associated with a purely graphical analysis of the spectral distribution. It also emphasizes the importance of considering the particle nature of light in research involving both visual and non-visual effects, which implies using the spectral distribution expressed in the photon system of units, a system that has been seldom used in lighting research for historical reasons. The authors encourage lighting engineers and researchers to determine which system is best suited to their work and then proceed with the correct use of spectral distributions and of spectral weighting functions for applications involving optical radiation.

Light-environment interactions and integrative lighting design: Connecting visual, non-visual and energy requirements in a case study experiment

Beyond vision, light influences human circadian rhythms and buildings' energy consumption. Design solutions are needed to satisfy visual and circadian requirements while minimizing lighting energy demands. By reflecting the incident radiation, inner surfaces influence spatial and spectral light distribution, affecting the energy needed to achieve task illuminance and light-induced circadian response. Here, the walls' spectral characteristics' impact on the overall luminous environment and power demands is analysed in a test room, combining seven walls' colours and three sources' correlated colour temperatures (CCTs). Hence, the luminaires are set to meet visual needs: eye level spectral irradiances are measured, and light-induced circadian responses are obtained regarding both circadian stimulus (CS) and melanopic equivalent daylight illuminance (mel-EDI). It is found that both parameters are higher for highly reflective walls or those most reflective in the short-wavelength interval, being insufficient for proper circadian stimulation according to current guidelines. For all colours, the highest mel-EDIs occur with 6000 K CCT and the lowest for 3000 K CCT. On the contrary, CSs are generally higher for 6000 K and lower for 4000 K. Second, the power demands necessary to meet circadian requirements are calculated. With warm sources, sufficient CS and mel-EDI values are achieved for similar eye-level illuminance, requiring similar light outputs and power demands regardless of the wall's colour. In all the other cases, the light outputs and the corresponding power demands to achieve mel-EDI = 136 lx are much lower than those to reach CS = 30%, while those to achieve mel-EDI = 250 lx are quite always the highest.

Time Evolving Photo Ionisation Device (TEPID): A novel code for out-of-equilibrium gas ionisation

Context. Photoionisation is one of the main mechanisms at work in the gaseous environment of bright astrophysical sources. A great deal of information on the gas physics, chemistry and kinematics, and on the ionising source itself, can be gathered through optical to X-ray spectroscopy. While several public time equilibrium photoionisation codes are readily available and can be used to infer average gas properties at equilibrium, time-evolving photoionisation models have only very recently started to become available. They are needed when the ionising source varies faster than the typical gas equilibration timescale. Using equilibrium models to analyse spectra of non-equilibrium photoionised gas may lead to inaccurate results, and prevents a solid assessment of gas density, physics, and geometry. Aims. Our main objective is to present and make available the Time-Evolving PhotoIonisation Device (TEPID), a new code that self-consistently solves time evolving photoionisation equations (both thermal and ionisation balance) and accurately follows the response of the gas to changes in the ionising source. Methods. TEPID self-consistently follows the gas temperature and ionisation in time by including all the main ionisation/recombination and heating/cooling mechanisms. The code takes in input the ionising light curve and spectral energy distribution and solves the time-evolving equations as a function of gas electron density and of time. The running time is intelligently optimised by an internal algorithm that initially scans the input light curve to set a time-dependent integration frequency. The code is built in a modular way, can be applied to a variety of astrophysical scenarios and produces time-resolved gas absorption spectra to fit the data. Results. To describe the structure and main features of the code, we present two applications of TEPID to two dramatically different astrophysical scenarios: the typical ionised absorbers observed in the X-ray spectra of active galactic nuclei (e.g. warm absorbers and ultra-fast outflows), and the circumburst environment of a gamma-ray burst. For both cases we show how the gas energy and ionisation balances vary as a function of time, gas density and distance from the ionising source. We show that time-evolving photoionisation leads to unique ionisation patterns that cannot be reproduced by stationary photoionisation codes when the gas is out of equilibrium. This demonstrates the need for codes such as TEPID in view of the unprecedented capabilities that will be offered by the upcoming high-resolution X-ray spectrometers on board missions like XRISM or Athena.

The effect of light intensity, spectrum, and photoperiod on the physiological performance of Asparagopsis taxiformis tetrasporophytes

Over the last several years there has been increased interest in large scale cultivation of the red seaweed Asparagopsis taxiformis due to its ability to reduce methane emissions in ruminant animals. However, research focused on developing strategies to optimize culture conditions for this alga is still relatively scarce. Both light quality and quantity are widely known to differentially influence any alga's photosynthetic rates, metabolic budgets and ultimately biomass and bio-active compound production. Optimization of cultivation conditions for algae requires the understanding and fine-tuning of light parameters including Photon Flux Density (PFD), light spectrum, and photoperiod, as well as culture density which largely governs light quantity (PFD) and quality (spectrum) within the culture. Here we explore the effects of light intensity, spectral light distribution, and day length on the physiological performance of the tetrasporophyte stage of A. taxiformis in culture using a series of experiments. The results were used to characterize the optimal light and biomass density range for cultivation, and a model was developed to optimize the light path in a cultivation vessel. Spectral light optimization revealed a significant reduction in cyanobacterial contamination for cultures illuminated with blue LED light. Artificially extending light duration longer than 12 h per day did not improve algal growth. The insights gained from these experimental results may be used to inform the design of tank-based A. taxiformis cultivation systems to support high yield and stable production of this emerging commercial crop.

Tomato Fruit Growth and Nutrient Accumulation in Response to Blue and Red Light Treatments during the Reproductive Growth Stage

Tomatoes are an important fruit consumed worldwide. Within protected cultivation environments, artificial light using energy-efficient light-emitting diodes can be applied in tomato production as an effective way to improve productivity and nutritional value. Several studies have investigated the effects of supplementing artificial light on various aspects of tomato growth, encompassing flowering, fruit development, ripening, and nutritional composition. However, the outcomes of previous studies offer inconclusive insights into whether the observed impacts on tomato growth have resulted from the provision of additional photons or discrepancies in the spectral distribution of light during artificial light supplementation. Within this context, this study aimed to specifically explore the independent effects of monochromatic blue and red light, along with their dichromatic mixture (blue + red), on fruit growth and nutrient accumulation in comparison with multispectral white light. These four different light treatments were implemented after anthesis under the same photosynthetic photon flux density to mitigate possible variabilities arising from different light intensities and originating during the vegetative growth stage. As a result, under the same light intensity conditions, red and blue + red light irradiance during the reproductive growth stage delayed fruit ripening by up to 4.33 days compared to white light. Regarding fruit productivity, the fresh weight of fully ripe tomato fruit in the blue, red, or blue + red light treatment groups was not different from that in the white-light treatment group, whereas the blue light treatment significantly reduced the number of fruits in the plant. Finally, nutrient content, including soluble sugars, lycopene, and β-carotene, significantly increased by 10.0%, 27.1%, and 65.2%, respectively, in the blue compared to the white light-irradiated group. This study demonstrated that the application of distinct light spectra during the reproductive growth phase could have varying impacts on tomato fruit development and nutrient accumulation. By integrating our findings with results from prior studies, a more efficient light intervention strategy could be developed to effectively regulate traits of tomato fruit within an indoor production system.

Antares I: a Modular Photobioreactor Suitable for Photosynthesis and Bioenergetics Research

Oxygenic photosynthesis is responsible for most of the fixation of atmospheric CO2. The microalgal community can transport atmospheric carbon into biological cycles in which no additional CO2 is created. This represents a resource to confront the actual climate change crisis. These organisms have evolved to adapt to several environments and different spectral distribution of light that may strongly influence their metabolism. Therefore, there is a need for development of photobioreactors specialized in addressing spectral optimization. Here, a multi-scale modular photobioreactor made from standard glass materials, ad hoc light circuits, and easily accessible, small commercial devices is described. The system is suitable to manage the principal culture variables of research in bioenergetics and photosynthesis. Its performance was tested by growing four evolutionary-distant microalgal species with different endosymbiotic scenarios: Chlamydomonasreinhardtii (Archaeplastida, green primary plastid), Polytomella parva (Archaeplastida, colorless plastid), Euglena gracilis (Discoba, green secondary plastid), and Phaeodactylum tricornutum (Stramenophiles, red secondary plastid). Our results show an improvement of biomass production, as compared to the traditional flask system. The modulation of the incident light spectra allowed us to observe a far-red adaptation in Euglenagracilis with a difference on paramylon production, and it also significantly increased the maximal cell density of the diatom species under green light. Together, these confirm that for photobioreactors with artificial light, manipulation of the light spectrum is a critical parameter for controlling the optimal performance, depending on the downstream goals.

Applied Photometry: Review of Retrospective and Reality Part 1: Candela and Watt, from Incandescent Lamp to LED

Photometry is the science of measuring light, which began with a visual comparison of the light of stars, the moon, and the sun with the light of a candle. Today it is a part of optical radiometry, inextricably linked with physical radiation detectors, taking into account the fact that light is actinic radiation, and physical detectors must be actinic in the case of integral measurements. At the same time, optical radiometry has introduced and introducing new technologies into spectral radiometric measurement methods, which, in turn, make it possible to solve the problems of measuring the parameters of actinic radiation by objective physical methods of spectral radiometry, taking into account the weight functions of actinic radiation. The choice between integral and spectral methods is determined by: – The required accuracy of the measurement task to be solved; – Knowledge of the weight functions of actinic radiation; – The quality of correction of radiation receivers for the weight functions of actinic radiation; – Methods for calibrating radiation receivers; – Actinic coefficients of optical radiation receivers (correction coefficients) and the accuracy of their determination; – Technical capabilities of spectral equipment; – Methods and means of spectrometers calibration; – Software for spectral measuring instruments, – Comparative analysis of the accuracy (uncertainty) of measurements by the spectral and integral methods in each individual case. The replacement of traditional sources of general lighting and signaling by radiation sources with LEDs, which have a spectral distribution of light emitting characteristics different from traditional light sources, has raised a number of issues in the metrological support of optical radiometry and applied photometry related to the oneness of the reproduction of units of energy and photometric quantities based on Watt.

A numerical study on the role of instabilities on multi-wavelength emission signatures of blazar jets

Context. Blazars, a class of active galaxies whose jets are relativistic and collimated flows of plasma directed along the line of sight, are prone to a slew of magnetohydrodynamic (MHD) instabilities. These jets show characteristic multi-wavelength and multi-timescale variabilities. Aims. We aim to study the interplay of radiation and particle acceleration processes in regulating the multi-band emission and variability signatures from blazars. In particular, the goal is to decipher the impact of shocks arising due to MHD instabilities in driving the long-term variable emission signatures from blazars. Methods. To this end, we performed relativistic MHD (RMHD) simulations of a representative section of a blazar jet. The jet was evolved using a hybrid Eulerian-Lagrangian framework to account for radiative losses due to synchrotron process as well as particle acceleration due to shocks. Additionally, we incorporated and validated radiative losses taking into consideration the external Compton (EC) process that is relevant for blazars. We further compared the effects of different radiation mechanisms through numerical simulation of 2D slab jet as a validation test. Finally, we carried out a parametric study to quantify the effect of magnetic fields and external radiation field characteristics by performing 3D simulations of a plasma column. The synthetic light curves and spectral energy distribution (SEDs) were analyzed to qualitatively understand the impact of instability driven shocks. Results. We observed that shocks produced with the evolution of instabilities give rise to flaring signatures in the high-energy band. The impact of such shocks is also evident from the instantaneous flattening of the synchrotron component of the SEDs. At later stages, we observed the transition in X-ray emission from the synchrotron process to that dominated by EC. The inclusion of the EC process also gives rise to γ-ray emission and shows signatures of mild Compton dominance that is typically seen in low-synchrotron peaked blazars.

The power of light: Impact on the performance of biocontrol agents under minimal nutrient conditions.

The spectral distribution of light (different wavelength) has recently been identified as an important factor in the dynamics and function of leaf-associated microbes. This study investigated the impact of different wavelength on three commercial biocontrol agents (BCA): Bacillus amyloliquefaciens (BA), Pseudomonas chlororaphis (PC), and Streptomyces griseoviridis (SG). The impact of light exposure on sole carbon source utilization, biofilm formation, and biosurfactant production by the selected BCA was studied using phenotypic microarray (PM) including 190 sole carbon sources (OmniLog®, PM panels 1 and 2). The BCA were exposed to five monochromatic light conditions (420, 460, 530, 630, and 660 nm) and darkness during incubation, at an intensity of 50 μmol m-2 s-1. Light exposure together with specific carbon source increased respiration in all three BCA. Different wavelengths of light influenced sole carbon utilization for the different BCA, with BA and PC showing increased respiration when exposed to wavelengths within the blue spectrum (420 and 460 nm) while respiration of selected carbon sources by SG increased in the presence of red light (630 and 660 nm). Only one carbon source (capric acid) generated biosurfactant production in all three BCA. A combination of specific wavelength of light and sole carbon source increased biofilm formation in all three BCA. BA showed significantly higher biofilm formation when exposed to blue (460 nm) and green (530 nm) light and propagated in D-sucrose, D-fructose, and dulcitol. PC showed higher biofilm formation when exposed to blue light. Biofilm formation by SG increased when exposed to red light (630 nm) and propagated in citraconic acid. To increase attachment and success in BCA introduced into the phyllosphere, a suitable combination of light quality and nutrient conditions could be used.

Assessment of melanopsin-based quantities: Comparison of selected design tools and validation against on-field measurements

Melanopsin-based quantities (circadian stimulus and melanopic illuminance) depend on the spectral irradiance at the eye level, in turn resulting from the light sources' spectral power distribution and the interactions between light and materials. Software used in design practice (as DIALux) do not consider light and materials' spectral characteristics. Consequently, circadian stimulus and melanopic illuminance are calculated based on the illuminance at the eye and the sources' spectrum. Although software including spectral interactions (as ALFA - Adaptive Lighting for Alertness) exist, it is not clear how much the accuracy of various modelling approaches affects melanopsin-based quantities assessment. This research aims at investigating the applicability of the popular lighting design software for evaluating non-visual effects. For this purpose, two different approaches, based on the use of ALFA (method A) and DIALux (method B) are described, validated against on-field measurements and compared. Spectral irradiance is measured at the work plane and at the eye in a test room where the walls' finishes and the luminaires’ spectrum are changed, obtaining 21 scenarios. When simulating the space with the two methods, acceptable results are obtained for horizontal illuminance (percentage errors within the range ±10%), whereas for the vertical plane, errors depend on the software and the lighting scenario. Overall, method A performs better than B, but it gives percentage errors trespassing ±10% in 38.10% and 52.38% of the scenes in estimating circadian stimulus and melanopic illuminance respectively. This research informs ALFA and DIALux users on the reliability of both simulation tools in melanopsin-based quantities evaluation.

A new method for finding nearby white dwarfs exoplanets and detecting biosignatures

ABSTRACT We demonstrate that the James Webb Space Telescope (JWST) can detect infrared (IR) excess from the blended light spectral energy distribution of spatially unresolved terrestrial exoplanets orbiting nearby white dwarfs. We find that JWST is capable of detecting warm (habitable-zone; Teq = 287 K) Earths or super-Earths and hot (400–1000 K) Mercury analogues in the blended light spectrum around the nearest 15 isolated white dwarfs with 10 h of integration per target using MIRI’s medium-resolution spectrograph (MRS). Further, these observations constrain the presence of a CO2-dominated atmosphere on these planets. The technique is nearly insensitive to system inclination, and thus observation of even a small sample of white dwarfs could place strong limits on the occurrence rates of warm terrestrial exoplanets around white dwarfs in the solar neighbourhood. We find that JWST can also detect exceptionally cold (100–150 K) Jupiter-sized exoplanets via MIRI broad-band imaging at $\lambda = 21\, \mathrm{\mu m}$ for the 34 nearest (<13 pc) solitary white dwarfs with 2 h of integration time per target. Using IR excess to detect thermal variations with orbital phase or spectral absorption features within the atmosphere, both of which are possible with long-baseline MRS observations, would confirm candidates as actual exoplanets. Assuming an Earth-like atmospheric composition, we find that the detection of the biosignature pair O3+CH4 is possible for all habitable-zone Earths (within 6.5 pc; six white dwarf systems) or super-Earths (within 10 pc; 17 systems) orbiting white dwarfs with only 5–36 h of integration using MIRI’s low-resolution spectrometer.

The Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER). IV. Star Cluster Catalog

We construct a catalog of star clusters from Hubble Space Telescope images of the inner disk of the Triangulum Galaxy (M33) using image classifications collected by the Local Group Cluster Search, a citizen science project hosted on the Zooniverse platform. We identify 1214 star clusters within the Hubble Space Telescope imaging footprint of the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. Comparing this catalog to existing compilations in the literature, 68% of the clusters are newly identified. The final catalog includes multiband aperture photometry and fits for cluster properties via integrated light spectral energy distribution fitting. The cluster catalog’s 50% completeness limit is ∼1500 M ☉ at an age of 100 Myr, as derived from comprehensive synthetic cluster tests.

Spectral light distribution affects photosynthesis, leaf reflective indices, antioxidant activity and growth of Vanilla planifolia

Vanilla planifolia is an obligate sciophyte (shade plant) with crassulacean acid metabolism (CAM) photosynthesis. Plants were grown for 12 months under black, blue, green, or red photoselective shade netting (PSN) to alter the spectral light distribution impacting the plants. Light wavelengths were measured in each treatment and plants were assessed for photosynthetic characteristics, leaf chlorophyll index (LCI), maximum quantum yield of photosystem II, leaf reflectance indices, leaf area, growth, antioxidant enzymes, lipid peroxidation, reactive oxygen species (ROS), and osmolyte content. Plants grown under red PSN had a higher quantity of red and far-red light and had greater nocturnal net CO2 assimilation (NocA), leaf area and leaf dry weight than plants in the other treatments. Plants grown under blue PSN had a higher quantity of blue light, resulting in a higher LCI and maximum quantum yield than plants in the other treatments. Plants grown under the red and blue PSN had increased leaf spectral reflectance indices compared to plants in the other treatments, which resulted in the highest levels of antioxidant scavenging enzymes, ascorbic acid (AsA), proline, and glycine betaine, and the lowest levels of H2O2. These findings demonstrate that increasing light in the red and far-red or blue portions of the spectrum by using PSN alters the photosynthetic and/or antioxidant responses of V. planifolia and increasing red and far-red light by using red PSN can also accelerate plant growth, possibly due to higher photosynthesis.

Analysis of Illumination Generated by LED Matrices Distribution

Сreation of indoor lighting systems with the possibility of changing its parameters in space and time is a promising direction within the framework of the intellectual environment system. The aim of this work was to create a methodology for calculating the illumination created by LED matrices which does not require the use of specialized software products and is adapted to the possibility of varying the parameters of LEDs and illuminated rooms.The urgency of creating a room lighting system that simulates the conditions of natural lighting taking into account the need to change its spectral composition in time, in space taking into account the physical and psychological state of a person is substantiated. The possibility of using well-known computer programs to calculate the distribution of illumination in the room is analyzed.A method has been developed for calculating the distribution of illumination on a plane using both a flat LED matrix and a matrix with an inclined arrangement of the planes of individual LEDs. It is shown that the distribution of illumination is a function of the indicatrix of the light intensity of the LED, its location in space, the number of LEDs in the matrix.Illumination distribution has been calculated for various light sources consisting of RGB LEDs both for desktop and ceiling lighting was calculated. It is established that when using matrices containing the same LEDs distribution of illumination is very nonuniform. The inclined arrangement of LED planes slightly increases uniformity reducing the maximum illumination. For ceiling lighting the option of uniform distribution of LEDs within the ceiling plane provides more uniform illumination than when the same number of LEDs are arranged in groups of matrices.Results of LED sources modeling indicate the need to modernize simple orthogonal matrices containing the same type of elements with the same power modes for all elements in order to increase the uniformity of illumination and efficiency. Such modernization can be carried out by changing the geometry of matrices differentiating the power modes of individual LEDs. The developed calculation program can be supplemented with options for introducing the above changes, as well as options for analyzing the spectral distribution of light in space.

Influence of transmissometers’ light source spectral distribution in measuring visibility

Presently, the difference in the spectral distribution of light sources is not been sufficiently taken into account when measuring and calibrating the transmissometers. As such, the visibility measurement result cannot be to be traced to the World Meteorological Organization (WMO) definition of meteorological optical range (MOR). In this study, a method is proposed to trace the spectral distribution of transmissometers’ light sources to the 2700 K incandescent light’s spectral distribution in MOR definition. Then a traceability basis of the light source’s spectral distribution is proposed, and a model is established to determine the influence of the light source’s absolute color temperature on the MOR measurement accuracy. At the transmissometers’ typical baseline lengths of 10, 20, 30, 50, and 75 m, the absolute color temperature range and their corresponding spectral simulation error range equivalent to 2700 K incandescent lamp are obtained. Finally, the Monte Carlo method is used to simulate and analyze the MOR error corresponding to the absolute color temperature of different spectral simulation errors at five typical baseline lengths. The results show that in 10 m–600 m of MOR, the maximum simulated MOR absolute error is 42 m, which is less than 50 m, in 600 m–1500 m of MOR, the maximum simulated MOR relative error is 2.9%, which is much lower than 10% and in 1500 m–10 km of MOR, the maximum simulated MOR relative error is 18.6%, which is less than 20%, the MOR measurement accuracy is improved to the International Civil Aviation Organisation (ICAO)’s recommended requirements, thus confirming the accuracy of our theoretical research. We expect that this work will help establish the standard procedure for the SI-traceable calibration of transmissometers.

Calibration of a Hyper-Spectral Imaging System Using a Low-Cost Reference.

In this paper, we present a hyper-spectral imaging system and practical calibration procedure using a low-cost calibration reference made of polytetrafluoroethylene. The imaging system includes a hyperspectral camera and an active source of illumination with a variable spectral distribution of intensity. The calibration reference is used to measure the relative reflectance of any material surface independent of the spectral distribution of light and camera sensitivity. Winter road conditions are taken as a test application, and several spectral images of snow, icy asphalt, dry asphalt, and wet asphalt were made at different exposure times using different illumination spectra. Graphs showing measured relative reflectance for different road conditions support the conclusion that measurements are independent of illumination. Principal component analysis of the acquired spectral data for road conditions shows well separated data clusters, demonstrating the system’s suitability for material classification.

Rayleigh-Brillouin scattering in binary mixtures of disparate-mass constituents: SF_{6}-He,SF_{6}-D_{2}, and SF_{6}-H_{2}.

The spectral distribution of light scattered by microscopic thermal fluctuations in binary mixture gases was investigated experimentally and theoretically. Measurements of Rayleigh-Brillouin spectral profiles were performed at a wavelength of 532nm and at room temperature, for mixtures of SF_{6}-He,SF_{6}-D_{2}, and SF_{6}-H_{2}. In these measurements, the pressure of the gases with heavy molecular mass (SF_{6}) is set at 1bar, while the pressure of the lighter collision partner was varied. In view of the large polarizability of SF_{6} and the very small polarizabilities of He, H_{2}, and D_{2}, under the chosen pressure conditions these low mass species act as spectators and do not contribute to the light scattering spectrum, while they influence the motion and relaxation of the heavy SF_{6} molecules. A generalized hydrodynamic model was developed that should be applicable for the particular case of molecules with heavy and light disparate masses, as is the case for the heavy SF_{6} molecule, and the lighter collision partners. Based on the kinetic theory of gases, our model replaces the classical Navier-Stokes-Fourier relations with constitutive equations having an exponential memory kernel. The energy exchange between translational and internal modes of motion is included and quantified with a single parameter z that characterizes the ratio between the mean elastic and inelastic molecular collision frequencies. The model is compared with the experimental Rayleigh-Brillouin scattering data, where the value of the parameter z is determined in a least-squares procedure. Where very good agreement is found between experiment and the generalized hydrodynamic model, the computations in the framework of classical hydrodynamics strongly deviate. Only in the hydrodynamic regime both models are shown to converge.

The relationship between internode elongation of soybean stems and spectral distribution of light in the canopy under different plant densities

ABSTRACT The present study carried out with a field plot experiment and light environment simulation experiment in 2017 to assess the effect of spectral distribution on internode elongation in soybean canopy. Henong 60 and Heinong 48 were used as the experimental materials. The spectral distribution in the soybean canopy was studied under four planting densities 200,000(D20), 300,000(D30), 400,000(D40) and 500,000(D50) plant ha−1. Meanwhile, a pot experiment of light environment simulation with light-emitting diode (LED) was carried out to further analyze the effects of light quantity and quality on the elongation of soybean seedlings. The results showed that the intensity of PAR, blue light, red light and far-red light in soybean canopy decreased by varying degrees with density and canopy depth increasing, and the decrease of PAR and R/FR led to significant elongation of internodes and plant height in high density. The spectral intensity in the middle and base of the canopy was strongly reduced, resulting in the strongest internode elongation in the middle of soybean stem. The increase in soybean plant height was also mainly due to the internode elongation in the middle at high density. In addition, the mono-light of far-red light could promote the internode elongation, while the red light and blue light acted as inhibitors and the inhibitory effect of blue light was even greater.

StainedView: Variable-Intensity Light-Attenuation Display with Cascaded Spatial Color Filtering for Improved Color Fidelity.

We present StainedView, an optical see-through display that spatially filters the spectral distribution of light to form an image with improved color fidelity. Existing light-attenuation displays have limited color fidelity and contrast, resulting in a degraded appearance of virtual images. To use these displays to present virtual images that are more consistent with the real world, we require three things: intensity modulation of incoming light, spatial color filtering with narrower bandwidth, and appropriate light modulation for incoming light with an arbitrary spectral distribution. In StainedView, we address the three requirements by cascading two phase-only spatial light modulators (PSLMs), a digital micromirror device, and polarization optics to control both light intensity and spectrum distribution. We show that our design has a 1.8 times wider color gamut fidelity (75.8% fulfillment of sRGB color space) compared to the existing single-PSLM approach (41.4%) under a reference white light. We demonstrated the design with a proof-of-concept display system. We further introduce our optics design and pixel-selection algorithm for the given light input, evaluate the spatial color filter, and discuss the limitation of the current prototype.