Distribution Of Diffuse Light Research Articles

Engineering of Diffuse Structural Colors

AbstractNowadays, structural colors successfully replace pigment‐based ones. Most of the newly proposed solutions rely on plasmonic systems, so speaking nanosized objects, exhibiting strongly size‐dependent optical properties. As a consequence, the fabrication requires high‐precision and time‐consuming technologies. A concept dealing with sub‐micronic surface features, easily reproducible on a large scale is proposed. The designed metasurface consists of randomly distributed holes serving both as cavity resonators and scatterers. The proposed solution grants an efficient control of the spatial distribution of diffuse light and offers a large palette of vibrant colors. The interferometric model and a two‐layer angular spectrum method provide a solid description of the physical origin of the phenomenon, with a high degree of agreement between simulations and experimental data.

Leaf shape, planting density, and nitrogen application affect soybean yield by changing direct and diffuse light distribution in the canopy

When attempting to maximize the crop yield from field-grown soybean (Glycine max (L.) Merr.) by means of improving the light conditions for photosynthesis in the canopy, it is crucial to find the optimal planting density and nitrogen application rate. The soybean plants that were the subject of our experiment were cultivated in N-dense mutual pairs, and included two cultivars with different leaf shapes; one cultivar sported ovate leaves (O-type) and the other lanceolate leaves (L-type). We analyzed the results quantitatively to determine the amount of spatial variation in light distribution and photosynthetic efficiency across the canopy, and to gauge the effect of the experimental parameters on the yield as well as the photosynthetic light and nitrogen use efficiency of the crop. Results indicate that the different leaf shapes were responsible for significant disparities between the photosynthetic utilization of direct and diffuse light. As the nitrogen fertilizer rate and the planting density increased, the soybean plants responded by adjusting leaf morphology in order to maximize the canopy apparent photosynthetic light use efficiency, which in turn affected the leaf nitrogen distribution in the canopy. Despite the fact that the light interception rate of the canopy of the L-type cultivar was lower than that of the canopy of the O-type cultivar, we found its canopy apparent photosynthetic nitrogen and light use efficiency were higher. It was interesting to note, however, that the nitrogen and light use efficiency contributions associated with exposure to diffuse light were greater for the latter than for the former.

A systematic bias in present models of circumsolar radiation

Light scattering by aerosol particles is known to be fairly largest modulator of circumsolar radiation, while its contribution to the direct beam irradiance progressively increases with atmospheric turbidity. Due to their forward-lobed radiation patterns, the large aerosol particles are of special importance in understanding the shaping of diffuse light distribution in the solar aureola. The mechanism of intensive small-angle scattering is the Fraunhofer diffraction which scales up linearly with the projected area (shadow) of each single particle.Theoretically founded models of circumsolar radiation usually rely on Mie scattering – a concept exclusively applicable to spherical particles. However, the particles occurring in nature typically have nonspherical shapes with aspect ratio exceeding a few times that for a sphere (for prolate particles) or smaller than unity (for oblate particles). Here we show that models based on Mie theory systematically underestimate circumsolar irradiance compared to what we can expect from nonspherical particles. The average brightening of solar corona due to nonspherical aerosols is 10–20%, but can be as large as 40–50% for needle-like or disk-like particles. We are introducing a correction factor to improve the accuracy of the present models.

Total and diffuse light distribution within the canopy of an apple orchard as affected by reflective ground covers

In recent years, anti-hail nets have been increasingly used to protect apple orchards. As they reduce the light intensity at canopy level, reflective ground covers are frequently placed on the soil surface before fruit harvest with the main aim to enhance color development in bicolored apples. It is not clear however, to which extent the light penetration inside the whole canopy is affected by the reflective ground covers. We performed a study in an intensively cultivated apple district of South Tyrol (northern Italy), with and without reflective ground covers. We measured light intensity at different heights from the ground and different distances from the tree trunk, using two instruments: an 80- cm long ceptometer and a point-like sensor capable of measuring the diffuse radiation component in addition to the total visible light. We found that the reflective ground cover significantly increased the quantity of diffuse light reflected from the orchard floor. The largest effect was recorded at 1 m height from the ground, but it was still significant at 2.5 m height. The influence of the reflective ground cover was particularly remarkable when sun and tree lines were aligned. The increase of total PAR inside the canopy due to the reflective material was however relatively small, suggesting a moderate effect on tree photosynthesis and therefore on apple yields.

Classification of diffuse light emission profiles for distinguishing skin layer penetration of a needle-free jet injection.

In this work, a system is developed for tracking the skin layer to which a needle-free jet injection of fluid has penetrated by incorporating a laser beam into the jet, and measuring the diffuse light emitted from skin tissue. Monitoring the injection in this way offers the ability to improve the reliability of drug delivery with this transdermal delivery method. A laser beam, axially aligned with a jet of fluid, created a distribution of diffuse light around the injection site that varied as the injection progressed. High-speed videography was used to capture the diffuse light emission from laser-coupled jet injections into samples of porcine skin, fat, and muscle. The injection produced a distribution of diffuse light around the injection site that varied as the injection descended. A classifier, trained to distinguish whether the light source was located in the fat or muscle from surface intensity profile measurements, correctly identified the injected layer in of the cases when cross-examined against estimates using the light distribution emitted from the side of the sample.

Estimating canopy gap fraction and diffuse light interception in 3D maize canopy using hierarchical hemispheres

Studying the detailed organization of plant canopy structure allows a better understanding of functional processes in functional-structural plant models (FSPM). Canopy gap fraction (CGF) is an important indicator describing the canopy structure and affects the way plants capture light to perform photosynthesis, especially the interception of diffuse light. Though efforts have been made to improve the accuracy and efficiency of CGF measurement and estimation, current technologies are usually position limited. Thus, this work developed new virtual methods for computing CGF and diffuse light interception in the 3D space of plant canopies. Five hierarchical hemispheres, containing 15, 40, 360, 1,440, and 5760 triangle patches, respectively, were constructed by applying Sqrt-3 and Butterfly subdivision schemes on an original icosahedron. Compared with traditional hemisphere division strategies using solid angles or crossed arcs of latitude and longitude, the proposed hierarchical hemispheres provide more resolution choices for different accuracy demands. Most of the patches on the hemispheres are regular triangles with similar sizes, which improves the CGF and diffuse light calculation accuracy using the Turtle model. Acceleration mechanism was built when calculating the detection of plant facets in the canopy using the tree relationship between adjacent hemispheres. Two geometric models and six maize canopy geometric models with cultivar and density differences were constructed using measured data to validate the approach. The maximum CGF error was 1.39% for the two geometric models. The average error of the four derived CGFs from hemisphere photographs was 4.23%. The diffuse light distribution correlation coefficients R2 were 0.96, 0.98, and 0.90 for three different canopy densities. Our algorithm provides multi-scale hemisphere choices for CGF and diffuse light interception simulation. The study also paves the way for further investigation into plant canopy structure analysis and simulation of light dynamics in plant canopies.

A Photometric Study of Giant Ellipticals and Their Stellar Halos With VST

Observations of diffuse starlight in the outskirts of galaxies are thought to be a fundamental source of constraints on the cosmological context of galaxy assembly in the Λ CDM model. Such observations are not trivial because of the extreme faintness of such regions. In this work, we investigated the photometric properties of six massive early-type galaxies (ETGs) in the VST Elliptical GAlaxies Survey (VEGAS) sample (NGC 1399, NGC 3923, NGC 4365, NGC 4472, NGC 5044, and NGC 5846) out to extremely low surface brightness levels with the goal of characterizing the global structure of their light profiles for comparison to state-of-the-art galaxy formation models. We carried out deep and detailed photometric mapping of our ETG sample taking advantage of deep imaging with VST/OmegaCAM in the g and i bands. By fitting the light profiles, and comparing the results to simulations of elliptical galaxy assembly, we have identified signatures of a transition between relaxed and unrelaxed accreted components and can constrain the balance between in situ and accreted stars. The very good agreement of our results with predictions from theoretical simulations demonstrates that the full VEGAS sample of ∼ 100 ETGs will allow us to use the distribution of diffuse light as a robust statistical probe of the hierarchical assembly of massive galaxies.

A Photometric Study of Giant Ellipticals and Their Stellar Halos With VST

Observations of diffuse starlight in the outskirts of galaxies are thought to be a fundamental source of constraints on the cosmological context of galaxy assembly in the Λ CDM model. Such observations are not trivial because of the extreme faintness of such regions. In this work, we investigated the photometric properties of six massive early-type galaxies (ETGs) in the VST Elliptical GAlaxies Survey (VEGAS) sample (NGC 1399, NGC 3923, NGC 4365, NGC 4472, NGC 5044, and NGC 5846) out to extremely low surface brightness levels with the goal of characterizing the global structure of their light profiles for comparison to state-of-the-art galaxy formation models. We carried out deep and detailed photometric mapping of our ETG sample taking advantage of deep imaging with VST/OmegaCAM in the g and i bands. By fitting the light profiles, and comparing the results to simulations of elliptical galaxy assembly, we have identified signatures of a transition between relaxed and unrelaxed accreted components and can constrain the balance between in situ and accreted stars. The very good agreement of our results with predictions from theoretical simulations demonstrates that the full VEGAS sample of ∼ 100 ETGs will allow us to use the distribution of diffuse light as a robust statistical probe of the hierarchical assembly of massive galaxies.

VEGAS: A VST Early-type GAlaxy Survey

Observations of diffuse starlight in the outskirts of galaxies are thought to be a fundamental source of constraint on the cosmological context of galaxy assembly in the ΛCDM model. Such observations are not trivial because of the extreme faintness of such regions. In this work, we investigated the photometric properties of six massive early-type galaxies (ETGs) in the VEGAS sample (NGC 1399, NGC 3923, NGC 4365, NGC 4472, NGC 5044, and NGC 5846) out to extremely low surface brightness levels with the goal of characterizing the global structure of their light profiles for comparison to state-of-the-art galaxy formation models. We carried out deep and detailed photometric mapping of our ETG sample taking advantage of deep imaging with VST/OmegaCAM in the g and i bands. By fitting the light profiles, and comparing the results to simulations of elliptical galaxy assembly, we have identified signatures of a transition between relaxed and unrelaxed accreted components and can constrain the balance between in situ and accreted stars. The very good agreement of our results with predictions from theoretical simulations demonstrates that the full VEGAS sample of ~100 ETGs will allow us to use the distribution of diffuse light as a robust statistical probe of the hierarchical assembly of massive galaxies.

Light propagation along the pericardium meridian at human wrist as evidenced by the optical experiment and Monte Carlo method.

To explore the characteristics of light propagation along the Pericardium Meridian and its surrounding areas at human wrist by using optical experiment and Monte Carlo method. An experiment was carried out to obtain the distribution of diffuse light on Pericardium Meridian line and its surrounding areas at the wrist, and then a simplified model based on the anatomical structure was proposed to simulate the light transportation within the same area by using Monte Carlo method. The experimental results showed strong accordance with the Monte Carlo simulation that the light propagation along the Pericardium Meridian had an advantage over its surrounding areas at the wrist. The advantage of light transport along Pericardium Merdian line was related to components and structure of tissue, also the anatomical structure of the area that the Pericardium Meridian line runs.

Statistical learning based facial animation

To synthesize real-time and realistic facial animation, we present an effective algorithm which combines image- and geometry-based methods for facial animation simulation. Considering the numerous motion units in the expression coding system, we present a novel simplified motion unit based on the basic facial expression, and construct the corresponding basic action for a head model. As image features are difficult to obtain using the performance driven method, we develop an automatic image feature recognition method based on statistical learning, and an expression image semi-automatic labeling method with rotation invariant face detection, which can improve the accuracy and efficiency of expression feature identification and training. After facial animation redirection, each basic action weight needs to be computed and mapped automatically. We apply the blend shape method to construct and train the corresponding expression database according to each basic action, and adopt the least squares method to compute the corresponding control parameters for facial animation. Moreover, there is a pre-integration of diffuse light distribution and specular light distribution based on the physical method, to improve the plausibility and efficiency of facial rendering. Our work provides a simplification of the facial motion unit, an optimization of the statistical training process and recognition process for facial animation, solves the expression parameters, and simulates the subsurface scattering effect in real time. Experimental results indicate that our method is effective and efficient, and suitable for computer animation and interactive applications.

Kubelka-Munk Model for Imperfectly Diffuse Light Distribution in Paper

Perfectly diffuse light is a fundamental assumption in the Kubelka-Munk (KM) model. This assumption is, however, seldom fulfilled by real media. In this work, we build a bridge between a weakly absorbing medium with an imperfectly diffuse light distribution and the corresponding KM model relying on a perfectly diffuse light distribution. We multiply the apparent K and S phenomenal coefficients deduced from a learning set medium by a scaling factor expressing the ratio of light diffuseness between the target medium and the learning set medium. For the target medium, thanks to this diffuseness scaling factor, theoretically predicted reflection and transmission spectra agree with the corresponding measured spectra. The illumination geometry, the optical properties and the thickness of the medium have an impact on the light diffuseness and therefore on the proposed diffuseness scaling factor.

Realtime light dosimetry software tools for interstitial photodynamic therapy of the human prostate

Photodynamic therapy (PDT) for the treatment of prostate cancer has been demonstrated to be a safe treatment option capable of inducing tissue destruction and decreasing prostate specific antigen (PSA) levels. However, prostate-PDT results in large intra- and interpatient variations in treatment response, possibly due to biological variations in tissue composition and short-term response to the therapeutic irradiation. Within our group, an instrument for interstitial PDT on prostate tissue has been developed that combines therapeutic light delivery and monitoring of light transmission via numerous bare-ended optical fibers. Here, we present algorithms that utilize data on the light distribution within the target tissue to provide realtime treatment feedback based on a light dose threshold model for PDT. This realtime dosimetry module is implemented to individualize the light dose and compensate for any treatment-induced variations in light attenuation. More specifically, based on the light transmission signals between treatment fibers, spatially resolved spectroscopy is utilized to assess the effective attenuation coefficient of the tissue. These data constitute input to a block-Cimmino optimization algorithm, employed to calculate individual fiber irradiation times provided the requirement to deliver a predetermined light dose to the target tissue while sparing surrounding sensitive organs. By repeatedly monitoring the light transmission signals during the entire treatment session, optical properties and individual fiber irradiation times are updated in realtime. The functionality of the algorithms is tested on diffuse light distribution data simulated by means of the finite element method (FEM). The feasibility of utilizing spatially resolved spectroscopy within heterogeneous media such as the prostate gland is discussed. Furthermore, we demonstrate the ability of the block-Cimmino algorithm to discriminate between target tissue and organs at risk (OAR). Finally, the realtime dosimetry module is evaluated for treatment scenarios displaying spatially and temporally varying light attenuation levels within the target tissue. We conclude that the realtime dosimetry module makes it possible to deliver a certain light dose to the target tissue despite spatial and temporal variations of the target tissue optical properties at the therapeutic wavelength.

The mass distribution in early-type disc galaxies: declining rotation curves and correlations with optical properties

We present rotation curves for 19 early-type disc galaxies (S0-Sab). The galaxies span a B-band absolute magnitude range from -17.5 to -22, but the majority have a high luminosity with M-B <-20. Rotation velocities are measured from a combination of H I velocity fields and long-slit optical emission line spectra along the major axis; the resulting rotation curves probe the gravitational potential on scales ranging from 100 pc to 100 kpc. We find that the rotation curves generally rise rapidly in the central regions and often reach rotation velocities of 200-300 km s(-1) within a few hundred parsecs of the centre. The detailed shape of the central rotation curves shows a clear dependence on the concentration of the stellar light distribution and the bulge-to-disc luminosity ratio: galaxies with highly concentrated stellar light distributions reach the maximum in their rotation curves at relatively smaller radii than galaxies with small bulges and a relatively diffuse light distribution. We interpret this as a strong indication that the dynamics in the central regions are dominated by the stellar mass. At intermediate radii, many rotation curves decline, with the asymptotic rotation velocity typically 10-20 per cent lower than the maximum. The strength of the decline is correlated with the total luminosity of the galaxies, more luminous galaxies having on average more strongly declining rotation curves. At large radii, however, all declining rotation curves flatten out, indicating that substantial amounts of dark matter must be present in these galaxies too. A comparison of our rotation curves with the Universal Rotation Curve from Persic et al. reveals large discrepancies between the observed and predicted rotation curves; we argue that rotation curves form a multiparameter family which is too complex to describe with a simple formula depending on total luminosity only. In a number of galaxies from our sample, there is evidence for the presence of rapidly rotating gas in the inner few hundred parsecs from the centres. The inferred central masses and mass densities are too high to be explained by the observed stellar components and suggest the presence of supermassive black holes in these galaxies.

The kinematics of intracluster planetary nebulae and the on-going subcluster merger in the Coma cluster core

Aims. The Coma cluster is the richest and most compact of the nearby clusters, yet there is growing evidence that its formation is still on-going. A sensitive probe of this evolution is the dynamics of intracluster stars, which are unbound from galaxies while the cluster forms, according to cosmological simulations. Methods. With a new multi-slit imaging spectroscopy technique pioneered at the 8.2 m Subaru telescope and FOCAS, we have detected and measured the line-of-sight velocities of 37 intracluster planetary nebulae associated with the diffuse stellar population of stars in the Coma cluster core, at 100 Mpc distance. Results. We detect clear velocity substructures within a 6 arcmin diameter field. A substructure is present at ~5000${\rm\,km\,s^{-1}}$, probably from in-fall of a galaxy group, while the main intracluster stellar component is centered around ~6500${\rm\,km\,s^{-1}}$, ~700${\rm\,km\,s^{-1}}$ offset from the nearby cD galaxy NGC 4874. The kinematics and morphology of the intracluster stars show that the cluster core is in a highly dynamically evolving state. In combination with galaxy redshift and X-ray data this argues strongly that the cluster is currently in the midst of a subcluster merger, where the NGC 4874 subcluster core may still be self-bound, while the NGC 4889 subcluster core has probably dissolved. The NGC 4889 subcluster is likely to have fallen into Coma from the eastern A2199 filament, in a direction nearly in the plane of the sky, meeting the NGC 4874 subcluster arriving from the west. The two inner subcluster cores are presently beyond their first and second close passage, during which the elongated distribution of diffuse light has been created. We predict the kinematic signature expected in this scenario, and argue that the extended western X-ray arc recently discovered traces the arc shock generated by the collision between the two subcluster gas halos. Any preexisting cooling core region would have been heated by the subcluster collision.

The Evolution of Galaxies in Clusters

We report on recent numerical investigations of the dynamical evolution of galaxies in clusters. Simulations of spiral galaxies falling into forming clusters show the development of the morphology-density relationship and the formation of regular and giant elliptical galaxies. The regular elliptical merger remnants end up in a fundamental plane very similar to the observed relation. The giant ellipticals have much in common with their real counterparts but their central velocity dispersions are too high. We also quantify the amount and distribution of diffuse light in clusters.

LIGHT RELATIONS OF TERRESTRIAL PLANT COMMUNITIES AND THEIR MEASUREMENT

Summary1. ‘Light’ covers a variety of related measures of radiant energy: the particular usage must be defined for each investigation.2. Light in the open varies in intensity and spectral composition, both with time and over space. These variations can usually be formulated mathematically and used to predict conditions in plant communities.3. Light may be measured directly with radiometric instruments, responding equally to all wavelengths within a certain waveband, or with photometric instruments, whose response approximates to that of the human eye. The use of the former is desirable whenever possible, as it simplifies subsequent interpretation of the results.4. Photographs covering an entire hemisphere can be used to estimate the contribution of diffuse and direct light separately under many circumstances. They are a great help with the interpretation of many forms of measurement.5. If the percentage of light transmitted by a plant community is to be treated as constant, diffuse and direct light must be treated separately. Even so, it is only the average transmission over considerable periods that is reasonably constant. The pattern of diffuse light distribution in the community is very different on clear and on cloudy days.6. In general, most diffuse light penetrates the plant community near the zenith. However, on clear days the aureole of light near the sun shining through a low‐altitude canopy gap may entirely alter this relationship.7. The distribution of direct light can be analysed from tracing the path of the sun across the canopy. The sun shines unobstructed through gaps of an angular width greater than 1/2.8. In some herbaceous communities the logarithm of relative intensity of diffuse light inside and outside the community is approximately proportional to the cumulative leaf area per unit area of ground above the level investigated. The relation varies with the angle of incidence of direct sunlight. The relation is not valid in all communities, and the errors involved in the assumption of its validity require further investigation.9. The leafy plant community reflects and transmits light selectively. It is important to allow for the interaction of changed spectral composition on the spectral sensitivity of the instrument when making estimates of albedo or percentage light transmission.10. Although the spectral characteristics of reflexion and transmission of individual leaves are nearly identical, this is not so for plant communities with a highly inhomo‐geneous structure.11. The percentage of total light transmitted usually increases with increasing cloud cover of the sky. The absolute intensity of diffuse light in the stand is usually higher when the sky is partly overcast than when the sky is entirely covered or clear. This is due to the increase of total light in the open with decrease of cloud cover, while the proportion of diffuse light in the total decreases with decrease in cloud cover. Provided the stand transmits more diffuse than direct light, the percentage transmission of the total will therefore fall as the total increases.12. Daily variation of diffuse light generally follows that in the open.13. In deciduous woods a light phase before leaf expansion and a shade phase after it can be distinguished. Each phase is characterized by a fairly constant percentage of diffuse light: that of direct light depends on daily and seasonal variation of solar altitude, increasing with increasing altitude.14. Light measurements given as percentages of that in the open may disguise important features of the variation of absolute amounts of light. Wherever possible these absolute quantities should be calculated. Where no direct meteorological data exist, it is often possible to make reasonable assumption from other data. The precise time, place and cloud conditions should be given for each measurement,15. Because of the great variety of instruments and techniques used, often inadequately described, comparison of results is nearly impossible. A thorough examination of the magnitude of the errors of each technique is badly needed.