Function Of Illumination Research Articles

Piezo-Phototronic Effect Controlled Dual-Channel Visible light Communication (PVLC) Using InGaN/GaN Multiquantum Well Nanopillars.

Visible light communication (VLC) simultaneously provides illumination and communication via light emitting diodes (LEDs). Keeping a low bit error rate is essential to communication quality, and holding a stable brightness level is pivotal for illumination function. For the first time, a piezo-phototronic effect controlled visible light communication (PVLC) system based on InGaN/GaN multiquantum wells nanopillars is demonstrated, in which the information is coded by mechanical straining. This approach of force coding is also instrumental to avoid LED blinks, which has less impact on illumination and is much safer to eyes than electrical on/off VLC. The two-channel transmission mode of the system here shows great superiority in error self-validation and error self-elimination in comparison to VLC. This two-channel PVLC system provides a suitable way to carry out noncontact, reliable communication under complex circumstances.

Detachment, displacement and reattachment activity in a freshwater byssate mussel (Limnoperna fortunei): the effects of light, temperature and substratum orientation

The ability of the freshwater bivalve Limnoperna fortunei to voluntarily detach from the substratum, crawl and reattach as a function of illumination, temperature, substratum orientation, and mussel size was investigated. Thirty-two per cent of the 879 experimental animals detached and reattached elsewhere at least once during five- to eight-day experiments. The proportions of mobile mussels were significantly higher in permanent darkness than under permanent illumination. Displacement distances were also higher in darkness, but statistical differences with illuminated individuals were inconclusive. No evidence of circadian rhythms was detected. Mobile mussels were often significantly smaller than non-mobile individuals. It was not possible to detect the effect of water temperature (22°C and 31°C), or substratum orientation (topside and underside) on mussel mobility, but because the power of the statistical tests was low, future experiments are needed to confirm this result. The ability of mussels to voluntarily detach and reattach elsewhere has important implications for biofouling control.

Constant illumination reduces circulating melatonin and impairs immune function in the cricket Teleogryllus commodus.

Exposure to constant light has a range of negative effects on behaviour and physiology, including reduced immune function in both vertebrates and invertebrates. It is proposed that the associated suppression of melatonin (a ubiquitous hormone and powerful antioxidant) in response to the presence of light at night could be an underlying mechanistic link driving the changes to immune function. Here, we investigated the relationship between constant illumination, melatonin and immune function, using a model invertebrate species, the Australian black field cricket, Teleogryllus commodus. Crickets were reared under either a 12 h light: 12 h dark regimen or a constant 24 h light regimen. Circulating melatonin concentration and immune function (haemocyte concentration, lytic activity and phenoloxidase (PO) activity) were assessed in individual adult crickets through the analysis of haemolymph. Constant illumination reduced melatonin and had a negative impact on haemocyte concentrations and lytic activity, but its effect on PO activity was less apparent. Our data provide the first evidence, to our knowledge, of a link between exposure to constant illumination and variation in haemocyte concentration in an invertebrate model, while also highlighting the potential complexity of the immune response following exposure to constant illumination. This study provides insight into the possible negative effect of artificial night-time lighting on the physiology of invertebrates, but whether lower and potentially more ecologically relevant levels of light at night produce comparable results, as has been reported in several vertebrate taxa, remains to be tested.

A uniqueness result for propagation-based phase contrast imaging from a single measurement

Phase contrast imaging seeks to reconstruct the complex refractive index of an unknown sample from scattering intensities, measured for example under illumination with coherent x-rays. By incorporating refraction, this method yields improved contrast compared to purely absorption-based radiography but involves a phase retrieval problem which, in general, allows for ambiguous reconstructions. In this paper, we show uniqueness of propagation-based phase contrast imaging for compactly supported objects in the near-field regime, based on a description by the projection- and paraxial approximations. In this setting, propagation is governed by the Fresnel propagator and the unscattered part of the illumination function provides a known reference wave at the detector which facilitates phase reconstruction. The uniqueness theorem is derived using the theory of entire functions. Unlike previous results based on exact solution formulae, it is valid for arbitrary complex objects and requires intensity measurements only at a single detector distance and illumination wavelength. We also deduce a uniqueness criterion for phase contrast tomography, which may be applied to resolve the three-dimensional structure of micro- and nano-scale samples. Moreover, our results may have some significance to electronic imaging methods due to the equivalence of paraxial wave propagation and Schrödinger’s equation.

Ptychographical imaging with partially saturated diffraction patterns

In ptychographical imaging with X-ray or electron beam, the recorded speckle intensity pattern of far field diffraction was often saturated by the presence of strong zeroth-order which was undesirable. A beam-stop was widely used to block the area of strong central diffraction in the pattern. The image was then reconstructed by disregarding the diffraction constraints within that area where inaccuracies exists due to saturation or blocking of the beam. Though reconstructions were obtained in this way by omitting saturation regions, the rationale behind this method was not discussed in detail and its effect on the final image quality was not studied. The physics of this method was analyzed theoretically and experimentally in this study. The convolution effect between illumination and object functions was able to retrieve and bring back the information lost in the blocked or saturated area from its neighborhood. This was possible while the saturated or blocked area was not wider than the spectral width of illumination, and once it exceeds this minimum, the quality of reconstruction would degrade seriously. The theoretical model was verified by numerical simulations and experiments.

Acoustoelectric photoresponse in graphene

The acoustoelectric current in graphene has been investigated as a function of illumination, using blue (450 nm) and red (735 nm) light-emitting diodes (LEDs), and surface acoustic wave (SAW) intensity and frequency. The measured acoustoelectric current increases with illumination, more than the measured change in the conductivity of the graphene, whilst retaining a linear dependence on the SAW intensity. The latter is consistent with the interaction between the carriers and SAWs being described by a relatively simple classical relaxation model suggesting that the change in the acoustoelectric current is caused by the effect of the illumination on the electronic properties of the graphene. The increase in the acoustoelectric current is greatest under illumination with the blue LED, consistent with the creation of a hot electron distribution.

Continuous motion scan ptychography: characterization for increased speed in coherent x-ray imaging.

Ptychography is a coherent diffraction imaging (CDI) method for extended objects in which diffraction patterns are acquired sequentially from overlapping coherent illumination spots. The object's complex transmission function can be reconstructed from those diffraction patterns at a spatial resolution limited only by the scattering strength of the object and the detector geometry. Most experiments to date have positioned the illumination spots on the sample using a move-settle-measure sequence in which the move and settle steps can take longer to complete than the measure step. We describe here the use of a continuous "fly-scan" mode for ptychographic data collection in which the sample is moved continuously, so that the experiment resembles one of integrating the diffraction patterns from multiple probe positions. This allows one to use multiple probe mode reconstruction methods to obtain an image of the object and also of the illumination function. We show in simulations, and in x-ray imaging experiments, some of the characteristics of fly-scan ptychography, including a factor of 25 reduction in the data acquisition time. This approach will become increasingly important as brighter x-ray sources are developed, such as diffraction limited storage rings.

Spectral‐domain solution to the electromagnetic scattering of a two‐dimensional beam by cylinders buried below a flat interface

ABSTRACTAn analytical‐numerical approach in the spectral domain is developed for the scattering problem by buried objects excited by a two‐dimensional illumination field. The scatterers are perfectly conducting cylinders, which are placed in a semi‐infinite medium below a flat interface. The source field is described by an arbitrary illumination function, and it is represented by means of its plane‐wave spectrum. The cylindrical‐wave approach is applied to represent the fields scattered by the cylinders. All the field contributions are expressed through spectral integrals, which allow to evaluate their interaction with the interface in terms of a superposition of monochromatic plane waves.Such integrals are evaluated in an accurate way, which can lead to results both in near‐field and far‐field regions. In this paper, the general theoretical approach is described, and numerical results are given for the case of an incident Gaussian beam. Two‐dimensional field maps in both the air and lower regions are reported in the case of one and two scatterers. An application of the technique to the diagnostic of reinforced concrete is reported, showing the use of the radar scattering cross‐section ratio to determine the size of rebar diameters. Modelling results validate the assumption proposed by other authors that the radar scattering cross‐section ratio can be used to determine rebar diameters using the monotonic behaviour observed at lower frequencies.

Electron transfer kinetics on natural crystals of MoS2 and graphite.

Here, we evaluate the electrochemical performance of sparsely studied natural crystals of molybdenite and graphite, which have increasingly been used for fabrication of next generation monolayer molybdenum disulphide and graphene energy storage devices. Heterogeneous electron transfer kinetics of several redox mediators, including Fe(CN)6(3-/4-), Ru(NH3)6(3+/2+) and IrCl6(2-/3-) are determined using voltammetry in a micro-droplet cell. The kinetics on both materials are studied as a function of surface defectiveness, surface ageing, applied potential and illumination. We find that the basal planes of both natural MoS2 and graphite show significant electroactivity, but a large decrease in electron transfer kinetics is observed on atmosphere-aged surfaces in comparison to in situ freshly cleaved surfaces of both materials. This is attributed to surface oxidation and adsorption of airborne contaminants at the surface exposed to an ambient environment. In contrast to semimetallic graphite, the electrode kinetics on semiconducting MoS2 are strongly dependent on the surface illumination and applied potential. Furthermore, while visibly present defects/cracks do not significantly affect the response of graphite, the kinetics on MoS2 systematically accelerate with small increase in disorder. These findings have direct implications for use of MoS2 and graphene/graphite as electrode materials in electrochemistry-related applications.

Intragap States Induced Visible Light Absorption of TiO2 Nanoparticles: En Route to Solar Fuel Production

ABSTRACTCarbon dioxide is the major greenhouse gas that is a bi-product of industrial approaches to energy production. Forests and nonagricultural lands act as a natural sink for CO2 removal from the atmosphere; however, the amount of emitted CO2 is significantly larger than the capacity of these natural sinks. This is particularly problematic as two cornerstones of our modern world, electricity generation and transportation, hold the largest share in greenhouse gas (such as CO2) emission. This leads to malignant impacts on the natural environment and human life, such as global warming. The obvious approach to reduce the amount of generated CO2 is to limit the use of fossil fuels. However, coal-fired power plants remain the largest source of electricity generation in 2014 and an equally potent and financially reasonable source is yet to be fully developed. Hence, new systems and strategies are crucial for the remediation of CO2. In this work, we present novel TiO2 nanoparticles, synthesized via a facile solution-phase method, which show a significant visible light absorption. The synthesized nanoparticles can be applied towards photoreduction of CO2 for hydrocarbon solar fuels production. A thorough photoemission spectroscopy analysis outlined the energy structure of the materials which uncovered a sub-bandgap absorption in the visible range due to the presence of intragap states. The origins of intragap states were investigated in greater detail using various characterization techniques. An in-depth chemical composition study of the developed material using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) indicated that the synthesized material is considerably un-doped. Further structural analysis using transmission electron microscopy (TEM) showed that distances between visible lattice fringes are matched with ordered crystalline phases of TiO2. The core emission study using XPS revealed that the oxygen vacancy defects in the structure--i.e. likely due the synthesis--are responsible for intragap states formation. Charge dynamics were investigated using Electron Paramagnetic Resonance (EPR) spectroscopy. EPR spectra were dominated by signals from oxygen-centered surface hole trapping sites with principle g values [2.003, 2.010, 2.023]--i.e. Ti4+ ˗ O2- on anatase. A faint signal was also observed as a function of visible light illumination at 5 K with principle g value of 1.975 that is suggestive of Ti3+ in rutile, a typical product of UV light exposure. In general, this study demonstrates the potential of a relatively inexpensive material for photoreduction of CO2 and generation of solar fuels.

LED板状肋片散热器性能的方向效应

The plate-fin heat sink is widely used in LED lamp for application of multi-angle illumination. According to the key structures of a LED projection lamp,the orientation effects on heat dissipation performance of plate-fin heat sink with natural convection cooling were researched under 3driving currents and 7 inclination angles between illumination direction and gravity direction. Based on the validity and accuracy of numerical simulation verified by experimental results,the thermal mechanisms with respect to maximum excess temperature and temperature uniformity were investigated through analyzing temperature and flow data derived from numerical simulation. The obvious differences of air velocity distribution in the flow channel of fins are found among inclination angles,these differences are the main reason of sensitive orientation effect about maximum excess temperature and temperature uniformity. In addition,air velocity difference between upstream and downstream around the measuring point with maximum temperature can be used to quantitatively interpret the variation trend of temperature uniformity in different inclination angles. Furthermore,the effects of inclination angle and fin spacing on the maximum excess temperature were analyzed. The results showthat the heat dissipation performance of plate-fin heat sink with optimal fin spacing has high orientation sensitivity,so the study of orientation effects on the air flow and heat transfer of plate-fin heat sinks is an indispensable task in the thermal design of LED with multi-angle illumination function.

Prospects of photon counting lidar for savanna ecosystem structural studies

Abstract. Discrete return and waveform lidar have demonstrated a capability to measure vegetation height and the associated structural attributes such as aboveground biomass and carbon storage. Since discrete return lidar (DRL) is mainly suitable for small scale studies and the only existing spaceborne lidar sensor (ICESat-GLAS) has been decommissioned, the current question is what the future holds in terms of large scale lidar remote sensing studies. The earliest planned future spaceborne lidar mission is ICESat-2, which will use a photon counting technique. To pre-validate the capability of this mission for studying three dimensional vegetation structure in savannas, we assessed the potential of the measurement approach to estimate canopy height in a typical savanna landscape. We used data from the Multiple Altimeter Beam Experimental Lidar (MABEL), an airborne photon counting lidar sensor developed by NASA Goddard. MABEL fires laser pulses in the green (532 nm) and near infrared (1064 nm) bands at a nominal repetition rate of 10 kHz and records the travel time of individual photons that are reflected back to the sensor. The photons’ time of arrival and the instrument’s GPS positions and Inertial Measurement Unit (IMU) orientation are used to calculate the distance the light travelled and hence the elevation of the surface below. A few transects flown over the Tejon ranch conservancy in Kern County, California, USA were used for this work. For each transect we extracted the data from one near infrared channel that had the highest number of photons. We segmented each transect into 50 m, 25 m and 10 m long blocks and aggregated the photons in each block into a histogram based on their elevation values. We then used an expansion window algorithm to identify cut off points where the cumulative density of photons from the highest elevation resembles the canopy top and likewise where such cumulative density from the lowest elevation resembles mean ground elevation. These cut off points were compared to DRL derived canopy and mean ground elevations. The correlation between MABEL and DRL derived metrics ranged from R2 = 0.70, RMSE = 7.9 m to R2 = 0.83, RMSE = 2.9 m. Overall, the results were better when analysis was done at smaller block sizes, mainly due to the large variability of terrain relief associated with increased block size. However, the increase in accuracy was more dramatic when block size was reduced from 50 m to 25 m than it was from 25 m to 10 m. Our work has demonstrated the capability of photon counting lidar to estimate canopy height in savannas at MABEL's signal and noise levels. However, analysis of the Advanced Topography Laser Altimeter System (ATLAS) sensor on ICESat-2 indicate that signal photons will be substantially lower than those of MABEL while sensor noise will vary as a function of solar illumination, altitude and declination, as well as the topographic and reflectance properties of surfaces. Therefore, there are reasons to believe that the actual data from ICESat-2 will give poorer results due to a lower sampling rate and use of only the green wavelength. Further analysis using simulated ATLAS data are required before more definitive results are possible, and these analyses are ongoing.

Research on Application of Intelligent Solar System in Stadium

With the development of national fitness activities, stadiums with all kinds of standards are established across the country. The functions of illumination and refrigeration inside stadiums have applied electricity. In order to save the consumption of energy, keep the sustainable development of society, as well as reinforce the consciousness of environmental protection, the thesis designs a set of novel light guided automatic lighting system of solar energy. The system realizes indoor illumination with controlling system. In the daytime, the system uses optical materials with automatic following lighting for indoor illumination, while uses stored energy of storage battery provided by daytime solar panel for LED illumination. The solar cell also provides energy for daytime automatic following lighting device. This device can take full advantage of solar energy to deal with the problem of energy waste, as well as proposes a new idea for energy conservation and emission reduction for stadiums.

Multiuser CSK scheme for indoor visible light communications.

Color Shift Keying (CSK) is a new modulation scheme for visible light communication systems using RGB LEDs which has been standardized in the PHY III level of the IEEE 802.15.7. This paper proposes some modifications so as to include multiuser capabilities provided by a time-based multiplexing, with the modulation constellation symbols being adapted to encode data with the luminux powers of the red, green and blue color bands respectively. This is achieved by employing a simple and low-complexity time-based pulse signals structure to separate the users' data symbols, while a three-dimensional signal constellation design is merged to improve data throughput. Numerical simulations are carried out to assess the performance of this novel architecture. The statistical properties of the transmitted RGB signals ensure dimming capabilities and that the illumination function is unaffected by flickering.

Nature of the Visual Loss in Observers With Leber's Congenital Amaurosis Caused by Specific Mutations in RPE65

To characterize visual losses associated with genetic mutations in the RPE65 gene that cause defects in the RPE-specific isomerase, RPE65. RPE65 is an important component of the retinoid cycle that restores 11-cis-retinal after its photoisomerization to its all-trans form. The defects investigated here cause Leber's congenital amaurosis (LCA2), an autosomal, recessively-inherited, severe, congenital-onset rod-cone dystrophy. Vision was assessed in nine patients and 10 normal controls by measuring: (1) long-wavelength sensitive (L-) cone temporal acuity (critical flicker fusion frequency or cff) as a function of target illuminance, and (2) L-cone temporal contrast sensitivity as a function of temporal frequency at a fixed-target illuminance. Measurements were made by modulating either a 650-nm light superimposed on a 480-nm background or the red phosphor of a color monitor on a background produced by the monitor's blue phosphor. RPE65-mutant observers have severely reduced cffs with shallower cff versus log illuminance functions that rise with a mean slope of 4.53 Hz per decade of illuminance compared with 8.69 Hz in normal controls. Consistent with the cff differences, RPE65-mutant observers show losses in temporal contrast sensitivity that increase rapidly with temporal frequency. All RPE65-mutant observers have consistent and substantial losses in temporal acuity and sensitivity compared with normal observers. The losses can be characterized by the addition of two sluggish filters within the mutant visual pathway, both filters with a time constant of 29.5 ms (i.e., low-pass filters with cut-off frequencies of 5.40 Hz).

A complete VLBI delay model for deforming radio telescopes: the Effelsberg case

Deformations of radio telescopes used in geodetic and astrometric very long baseline interferometry (VLBI) observations belong to the class of systematic error sources which require correction in data analysis. In this paper we present a model for all path length variations in the geometrical optics of radio telescopes which are due to gravitational deformation. The Effelsberg 100 m radio telescope of the Max Planck Institute for Radio Astronomy, Bonn, Germany, has been surveyed by various terrestrial methods. Thus, all necessary information that is needed to model the path length variations is available. Additionally, a ray tracing program has been developed which uses as input the parameters of the measured deformations to produce an independent check of the theoretical model. In this program as well as in the theoretical model, the illumination function plays an important role because it serves as the weighting function for the individual path lengths depending on the distance from the optical axis. For the Effelsberg telescope, the biggest contribution to the total path length variations is the bending of the main beam located along the elevation axis which partly carries the weight of the paraboloid at its vertex. The difference in total path length is almost $$-$$ 100 mm when comparing observations at 90 $$^\circ $$ and at 0 $$^\circ $$ elevation angle. The impact of the path length corrections is validated in a global VLBI analysis. The application of the correction model leads to a change in the vertical position of $$+120$$ mm. This is more than the maximum path length, but the effect can be explained by the shape of the correction function.

Ptychographic inversion via Wigner distribution deconvolution: noise suppression and probe design.

We reconsider the closed form solution of the ptychographic phase problem called the Wigner Distribution Deconvolution Method (WDDM), which has remained discarded for twenty years. Ptychographic reconstruction is nowadays always undertaken by iterative algorithms. WDDM gives rise to a 4 dimensional data cube of all the relative phases between points in the diffraction plane. Here we demonstrate a novel method to use all this information, instead of just the small subset used in the original 'stepping out' procedure developed in the 1990s, thus greatly suppressing noise. We further develop a method for designing an improved probe (illumination function) to further decrease noise effects during the deconvolution division. Combining these two with an iterative procedure for the deconvolution, which avoids the usual difficulty of a divide by a small number, we show in model calculations that WDDM competes well with the modern conventional iterative methods like ePIE (the extended Ptychographical Iterative Engine).

Two-dimensional Object Functions and Three-dimensional Illumination Functions: their Validity, Interaction and Utility

In high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) the data is generally interpreted as the convolution of the sample's sharply-peaked object function with the intensity of the real-valued point-spread function (PSF) of the illumination. As a single image is itself necessarily two-dimensional (2D) it is typically assumed that the object function and PSF can also be accurately described as 2D; this is the so-called 2D-object imaging assumption. Here the validity of these two-assumptions is evaluated using experimental HAADF STEM focal-series. It is found that the contrast contained in each image of the focal-series is accurately described by the convolution of a focus-invariant 2D object with a 2D optical-transfer function (OTF) which describes the illumination at the focus value used for imaging.

Variational Bayesian method for Retinex.

In this paper, we propose a variational Bayesian method for Retinex to simulate and interpret how the human visual system perceives color. To construct a hierarchical Bayesian model, we use the Gibbs distributions as prior distributions for the reflectance and the illumination, and the gamma distributions for the model parameters. By assuming that the reflection function is piecewise continuous and illumination function is spatially smooth, we define the energy functions in the Gibbs distributions as a total variation function and a smooth function for the reflectance and the illumination, respectively. We then apply the variational Bayes approximation to obtain the approximation of the posterior distribution of unknowns so that the unknown images and hyperparameters are estimated simultaneously. Experimental results demonstrate the efficiency of the proposed method for providing competitive performance without additional information about the unknown parameters, and when prior information is added the proposed method outperforms the non-Bayesian-based Retinex methods we compared.

Reciprocal-space up-sampling from real-space oversampling in x-ray ptychography

We retrieve x-ray phase images from ptychographical data which, according to the conventional coherent diffractive imaging (CDI) criterion, have been grossly undersampled. Ptychographical data are intrinsically oversampled in real space, as the illumination function of subsequent exposures overlap. By exploiting the real-space redundancy in ptychography, we are able to recover the conventional CDI reciprocal sampling, despite an increase in the solid angle of the detector pixels. As a result the current experimental geometrical constraints placed upon probe size, object to detector distance, and pixel size are all relaxed.