Frontal Illumination Research Articles

Evaluation of front and backside performances of a large surface organic photovoltaic module under bifacial illumination

Semitransparency is one of the attractive characteristics of thin-film solar modules as it allows electricity generation while providing building illumination. However, enhancing transparency can result in lower energy generation efficiency. An effective way to improve energy production in semitransparent modules is through bifacial illumination. This work aims to evaluate, experimentally, and discuss the optical and electrical properties of a commercial, semitransparent organic photovoltaic (OPV) module under bifacial illumination. With that purpose, current-voltage characteristic curves were obtained under the following conditions: a) front, b) rear illumination and c) simultaneous illumination on both faces. The module was placed inside a V-trough cavity to implement electrical measurements with the module's both faces simultaneously illuminated by natural sunlight. Results show that bifacial illumination is an effective way to enhance energy production in semitransparent OPV devices, and a 46% increase in power generation compared to traditional illumination (frontal illumination) was achieved in the experiments. The backside illumination performance differs by over 40%, compared with the front side, due to electrode shading, optics, and differences in the energy conversion processes taking place in the active layer. The OPV module operation under bifacial illumination is equivalent to a parallel connection between the front and backside illumination performances. Optical modeling shows that the active layer absorbs a large part of the incoming light within the cell spectral response. Nevertheless, in the case of frontal illumination, a significant fraction of solar radiation in the visible region is transmitted and remains available, for instance, for building illumination purposes.

Парацентез передней камеры глаза при глаукоме как метод экстренного снижения внутриглазного давления у собак и кошек

The article presents the technique of paracentesis of the anterior chamber of the eye with simultaneous intra-chamber administration of 0,5% pilocarpine solution, to identify the dynamics of intraocular pressure reduction, as well as to determine the effectiveness of this procedure both immediately after its execution and in the long term; based on the analysis of the data obtained, to determine complications. The study included 37 animals (39 eyes): 24 dogs and 13 cats with glaucoma, which, according to the anamnesis, developed no more than 10 days. without any prior hypotensive treatment. All animals underwent paracentesis without the use of general anesthesia or sedation. The procedure was performed under 6x magnification using frontal illumination, with a 27G needle for 9 hours for the right eye and for 3 hours for the left eye. The puncture was carried out on the periphery of the cornea at a distance of 1 mm from the limb. The volume of aspirated intraocular fluid was no more than 2 drops. Then a 0,5 % solution of pilocarpine was injected into the anterior chamber through the opening of the paracentesis. The volume of the injected solution did not exceed 0,3 ml. After paracentesis and pilocarpine administration, dexamethasone solution was subconjunctively instilled in combination with gentamicin and novocaine. Then hypotensive therapy was prescribed from a combination of eye drops. The study shows that the method with simultaneous intra-chamber injection of 0,5 % pilocarpine solution is effective in dogs and cats without any pronounced side effects. These results allow us to suggest anterior chamber paracentesis as a procedure for emergency reduction of intraocular pressure, especially in acute attacks of glaucoma in dogs and cats.

Necrosis Depth and Photodynamic Threshold Dose with Redaporfin-PDT.

Predicting the extent of necrosis in photodynamic therapy (PDT) is critical to ensure that the whole tumor is treated but vital structures, such as major blood vessels in the vicinity of the tumor, are spared. The models developed for clinical planning rely on empirical parameters that change with the nature of the photosensitizer and the target tissue. This work presents an in vivo study of the necrosis in the livers of rats due to PDT with a bacteriochlorin photosensitizer named redaporfin using both frontal illumination and interstitial illumination. Various doses of light at 750nm were delivered 15min postintravenous administration of redaporfin. Sharp boundaries between necrotic and healthy tissues were found. Frontal illumination allowed for the determination of the photodynamic threshold dose-1.5×1019 photonscm-3 -which means that the regions of the tissues exposed to more than 11mm of ROS evolved to necrosis. Interstitial illumination produced a necrotic radius of 0.7cm for a light dose of 100Jcm-1 and a redaporfin dose of 0.75mgkg-1 . The experimental data obtained can be used to inform and improve clinical planning with frontal and interstitial illumination protocols.

Plasmonic Field Enhancement by Metallic Subwave Lattices on Silicon in the Near-Infrared Range

The enhancement of the electric field in plasmonic nanostructures on a Si substrate in the near-infrared range is studied theoretically. Two-dimensional square arrays of circular holes of various diameters in a gold film serve as metasurfaces allowing the conversion of the external electromagnetic radiation into surface plas-mon modes at the Au-Si interface. It is established that illumination of nanostructures from the side of the Si substrate provides a higher field enhancement compared to the case of frontal illumination, since the incident light wave in the former case reaches the gold interface without passage through subwavelength holes for which the transmittance is extremely low. The plasmonic field enhancement, as a function of the diameter of holes of the array, shows the maximum at which the Bloch plasmon polaritons propagating along the Au-Si interface are transformed to localized surface plasmon modes. Two types of localized plasmons are detected. The short-wavelength plasmon is excited along the array diagonals and exists at any angles of incidence of light on the structure. The long-wavelength plasmon occurs only at nonzero angles of incidence and is located along orthogonal directions parallel to the sides of the square array. These results are directly related to the problem of fabricating effective silicon photodetectors with quantum dots.

Indium tin oxide thin-films prepared by vapor phase pyrolysis for efficient silicon based solar cells

The vapor phase pyrolysis deposition method was developed for the preparation of indium tin oxide (ITO) thin films with thicknesses ranging between 300 and 400nm with the sheet resistance of 10–15Ω/sq. and the transparency in the visible region of the spectrum over 80%. The layers were deposited on the (100) surface of the n-type silicon wafers with the charge carriers concentration of ~1015cm−3. The morphology of the ITO layers deposited on Si wafers with different surface morphologies, e.g., smooth (polished), rough (irregularly structured) and textured (by inversed pyramids) was investigated. The as-deposited ITO thin films consist of crystalline columns with the height of 300–400nm and the width of 50–100nm. Photovoltaic parameters of mono- and bifacial solar cells of Cu/ITO/SiO2/n–n+Si/Cu prepared on Si (100) wafers with different surface structures were studied and compared. A maximum efficiency of 15.8% was achieved on monofacial solar cell devices with the textured Si surface. Bifacial photovoltaic devices from 100μm thick Si wafers with the smooth surface have demonstrated efficiencies of 13.0% at frontal illumination and 10% at rear illumination.

Motion and texture shape cues modulate perceived material properties.

Specular and matte surfaces can project identical images if the surface geometry and light field are appropriately configured. Our previous work has shown that the visual system can exploit stereopsis and contour cues to 3D shape to disambiguate different surface reflectance interpretations. Here, we test whether material perception depends on information about surface geometry provided by structure from motion and shape from texture. Different surface textures were superimposed on a fixed pattern of luminance gradients to generate two different 3D shape interpretations. Each shape interpretation of the luminance gradients promoted a different experience of surface reflectance and illumination direction, which varied from a specular surface in frontal illumination to a comparatively matte surface in grazing illumination. The shape that appeared most specular exhibited the steepest derivatives of luminance with respect to surface orientation, consistent with physical differences between specular and diffuse reflectance. The effect of apparent shape on perceived reflectance occurred for a variety of surface textures that provided either structure from motion, shape from texture, or both optical sources of shape information. In conjunction with previous findings (Marlow, Todorović, & Anderson, 2015; Marlow & Anderson, 2015), these results suggest that any cue that provides sufficient information about 3D shape can also be used to derive material properties from the rate that luminance varies as a function of surface curvature.

Image Generation Using Bidirectional Integral Features for Face Recognition with a Single Sample per Person.

In face recognition, most appearance-based methods require several images of each person to construct the feature space for recognition. However, in the real world it is difficult to collect multiple images per person, and in many cases there is only a single sample per person (SSPP). In this paper, we propose a method to generate new images with various illuminations from a single image taken under frontal illumination. Motivated by the integral image, which was developed for face detection, we extract the bidirectional integral feature (BIF) to obtain the characteristics of the illumination condition at the time of the picture being taken. The experimental results for various face databases show that the proposed method results in improved recognition performance under illumination variation.

Illumination compensation for facial feature point localization in a single 2D face image

Current researches have demonstrated that illumination variation on face images degrades the accuracy of facial identity and emotion recognition. To decrease the impact of illumination variation, researchers have proposed many creative methods of illumination compensation. However, these methods are limited in compensating for the shadow around the nose. On the basis of our previous researches, we now propose a novel approach which can effectively decrease the impact of illumination variation, especially the shadow around the nose. Firstly, we preprocessed the face image with uneven brightness using technologies of illuminant direction estimation and improved Retinex. Secondly, we turn the original face image into a binary image with only shadow region or non-shadow region using region growing technology. Thirdly, we calculate the difference between the intensity of the original input face image and the average intensity of the face images under the frontal illumination. Fourthly, for the face image preprocessed in the first step, we keep its non-shadow region. For the intensity difference, we extract its shadow region whose intensity is reduced by an adaptive value. Fifthly, we synthesize the non-shadow region and the shadow region in step four. Finally, we apply maximum filter to smooth the boundary between them. The proposed method is simple in computation and does not need any training steps or any knowledge of 3D models. The experimental results using extended Yale face database B show that our method achieves better illumination compensation comparing with the existing techniques, and provide more satisfactory experimental data for facial identity and emotion recognition.

Automated characterization and quantification of hydrocarbon seeps based on frontal illuminated video observations

Hydrocarbon releases, either natural or due to anthropogenic activities, are of major relevance for the marine environment. In this work we specify our approach to quantify these seeps by subsea imaging utilizing camera systems and frontal illumination setups on board remotely operated vehicles. This work showcases, based on a campaign in the region west of Svalbard, improved methodological guidelines for the seep quantification operation together with a novel automated post-mission evaluation. The comparison of automated quantification with manual information extraction illustrates the efficiency of this new method while processing comparable estimates of seep characteristics.

Towards efficient image irradiance modelling of convex Lambertian surfaces under single viewpoint and frontal illumination

Under local illumination assumption, phenomenological appearance models capture surface appearance through the mathematical modelling of the reflection process. Theoretically, due to the arbitrariness of the lighting function, the space of all possible images of a fixed-pose object under all possible illumination conditions is infinite dimensional. Nonetheless, due to their low- frequency nature, irradiance signals can be represented using low-order basis functions, where spherical harmonics (SH) has been extensively adopted. When capturing image irradiance from a single viewpoint, the visible part of the object's surface constructs the upper hemisphere of the surface normals where the SH is no longer orthonormal. In this paper, we propose the use of hemispherical harmonics (HSH) to model image irradiance of convex Lambertian objects perceived from single viewpoint under unknown distant as well as near illumination. We prove analytically, and validate experimentally, that the Lambertian reflectance kernel has a more compact harmonic expansion in the hemispherical domain when compared to its spherical counterpart. Our experiments illustrate that, despite of having poor approximation accuracy under very close lights, such behavior improves exponentially with little increase in the distance to the light source relative to the object size.

Face Recognition under Illumination Variation Using Shadow Compensation and Pixel Selection

We propose a robust face recognition method under illumination variation. By using shadow compensation methods, we restore the image of a facial image taken under arbitrary illumination into an image that is similar to the image taken with frontal illumination. Then we apply a pixel selection method to these restored images in order to reduce the noise components, which can interfere with the extraction of discriminant features for face recognition. The experimental results for the CMU-PIE, Yale B and Multi-PIE databases show that the proposed method results in the improvement of recognition performance under illumination variation.

Virtual illumination grid for correction of uncontrolled illumination in facial images

Face recognition under uncontrolled illumination conditions is still considered an unsolved problem. In order to correct for these illumination conditions, we propose a virtual illumination grid (VIG) approach to model the unknown illumination conditions. Furthermore, we use coupled subspace models of both the facial surface and albedo to estimate the face shape. In order to obtain a representation of the face under frontal illumination, we relight the estimated face shape. We show that the frontal illuminated facial images achieve better performance in face recognition. We have performed the challenging Experiment 4 of the FRGCv2 database, which compares uncontrolled probe images to controlled gallery images. Our illumination correction method results in considerably better recognition rates for a number of well-known face recognition methods. By fusing our global illumination correction method with a local illumination correction method, further improvements are achieved.

Active illumination and appearance model for face alignment

Illumination conditions have an explicit effect on the performance of face recognition systems. In particular, varying the illumination upon the face imposes such complex effects that the identification often fails to provide a stable performance level. In this paper, we propose an approach integrating face identity and illumination models in order to reach acceptable and stable face recognition rates. For this purpose, Active Appearance Model (AAM) and illumination model of faces are combined in order to obtain an illumination invariant face localization. The proposed method is an integrated Active Illumination and Appearance Model (AIA) which combines identity, illumination and shape components in a single model and allows us to control them, separately. One of the major advantage of the proposed AIA model is that efficient model fitting is achieved, whilst maintaining performance against illumination changes. In addition to model fitting, images illuminated from different directions can easily be synthesized by changing the parameters related to illumination modes. The method provides a practical approach, since only one image with frontal illumination of each person for training, is sufficient. There is no need to build complex models for illumination. As a result, this paper has presented a simple and efficient method for face modeling and face alignment in order to increase the performance of face localization by means of the proposed illumination invariant AIA method for face alignment, such as the Active Appearance Models, invariant to changes in illumination. From the experimental results, we showed that the proposed AIA model provides higher accuracy than classical Active Appearance Model for face alignment in a point-to-point error sense.

Histological analyses of thermal effect caused by 1.2 W diode laser irradiation at rat periodontal pockets

The aim of this in vivo study was to evaluate the thermal effects caused by 810 nm 1.2 W diode laser irradiation of periodontal tissues. Despite all data available concerning the laser application for periodontal treatment, one of the most relevant challenges is to prevent the harmful tissue heating induced by different clinical protocols. Periodontal pockets were induced at molars in 96 rats. Several irradiation powers under CW mode were investigated: 0, 400, 600, 800, 1000, 1200 mW. The pockets were irradiated using a 300 µm frontal illumination fiber. The animals were killed at 4 or 10 days after irradiation. The mandible was surgically removed and histologically processed. The histological sections stained with H/E demonstrated that irradiation parameters up to 1000 mW were thermally safe for the periodontal tissues. The sections stained with Brown & Brenn technique evidenced bacteria in the periodontal tissues. Consequently, the diode laser irradiation as a unique treatment was not capable to eliminate bacteria of the biofilm present in the pockets. According to the methodology used here, it was concluded that the thermal variation promoted by a diode laser can cause damage to periodontal tissues depending on the energy density used. The 1.2 W diode laser irradiation itself does not control the bacteria present in the biofilm of the periodontal pockets without mechanical action. The knowledge of proper high intensity laser parameters and methods of irradiation for periodontal protocols may prevent any undesirable thermal damage to the tissues.

Separating corneal reflections for illumination estimation

Eyes exhibit a significant amount of specular reflection and could be used to derive a detailed estimate of frontal illumination. To determine a more accurate estimate of illumination from the environment, iris color and texture should be separated from the specularly reflected light, since they may substantially obscure reflections of the scene. In this paper, a method is presented for separating corneal reflections in an image of human irises. We consider the iris texture to be diffuse, and the observed image color is produced as the sum of the diffuse component and the specular component. A number of methods have been proposed to separate or decompose these two components. To our knowledge, all methods that use a single input image demonstrated success in only limited cases, such as for uniform colored lighting and simple object textures. They are not applicable to irises, which exhibit intricate textures and complicated reflections of the environment. To make this problem feasible, our method capitalizes on physical characteristics of human irises to obtain an illumination estimate that encompasses the prominent light contributors in the scene. Results of the algorithm are presented for eyes of different colors, including light colored eyes for which reflection separation is necessary to determine a valid illumination estimate.

THE BIFACIAL CONVERTER OF SOLAR ENERGY IN ELECTRICAL ON THE BASE OF ISOTYPE HETEROJUNCTION

The method of n+Si/nSi/SiO2 /n+ITO bifacial solar cells fabrication by pyrolitical spraying was elaborated. This structure contains only isotype junctions. The spectral sensitivity is situated in the 350–1200nm wavelength region and is independent on the illumination direction. The photoelectrical parameters of solar cells obtained on silicon wafer (4,5 Ohm.cm) are following: at frontal illumination Voc=0,425V, Isc=32,63mA/cm2 , FF=68,3%, Eff=9,47%; at rear illumination Voc=0,392V, Isc =13,20mA/cm2 , FF=69,3%, Eff=3,60%.

A fast marching formulation of perspective shape from shading under frontal illumination

An adaptation of the fast marching method to the perspective Shape from Shading under frontal illumination is proposed. A heuristic is proposed to handle occlusion. The method outperforms Tankus et al. [Tankus, A., Sochen, N., Yeshurun, Y., 2005. Shape-from-shading under perspective projection. Internat. J. Comput. Vision 63(1), 21–43] in both time and accuracy. Accurate methods for generating testing images are also reported.

Illumination invariant face recognition

The appearance of a face will vary drastically when the illumination changes. Variations in lighting conditions make face recognition an even more challenging and difficult task. In this paper, we propose a novel approach to handle the illumination problem. Our method can restore a face image captured under arbitrary lighting conditions to one with frontal illumination by using a ratio-image between the face image and a reference face image, both of which are blurred by a Gaussian filter. An iterative algorithm is then used to update the reference image, which is reconstructed from the restored image by means of principal component analysis (PCA), in order to obtain a visually better restored image. Image processing techniques are also used to improve the quality of the restored image. To evaluate the performance of our algorithm, restored images with frontal illumination are used for face recognition by means of PCA. Experimental results demonstrate that face recognition using our method can achieve a higher recognition rate based on the Yale B database and the Yale database. Our algorithm has several advantages over other previous algorithms: (1) it does not need to estimate the face surface normals and the light source directions, (2) it does not need many images captured under different lighting conditions for each person, nor a set of bootstrap images that includes many images with different illuminations, and (3) it does not need to detect accurate positions of some facial feature points or to warp the image for alignment, etc.

Bower location and orientation in Satin Bowerbirds: optimising the conspicuousness of male display?

Male Satin Bowerbirds, Ptilonorhynchus violaceus, have been reported to construct their bowers with the decorated portion of the bower platform oriented northward. Given the regularity of this orientation, it has been suggested that the intensity and quality of incoming solar radiation may enhance male displays. However, previous reports of bower orientation originate from studies conducted in open-canopy, sclerophyll forest, where diel variation in the intensity of light striking the bower is mostly influenced by the altitude and azimuth of the sun. We studied 12 Satin Bowerbird bowers in the mountainous rainforest of the Atherton Tablelands, Australia, and found no significant tendency for bower platforms to face north. Instead, bowers were invariably constructed near canopy gaps, and there was a significant tendency for bowers to face away from these gaps. We suggest that this pattern of orientation allows displaying males to be illuminated predominantly from the front when viewed by females from within the bower avenue. There was also a significant positive association between bower orientation and the orientation of the slope of the hill on which the bower was constructed, such that bowers were oriented upslope, further enhancing frontal illumination. We suggest that Satin Bowerbirds may use a variety of means, including bower orientation, to achieve this objective.

The shadow telescope vs. 3-D video system—evaluation in standardised tasks

Today's endoscopes use a central frontal illumination, which creates huge contrast, no visible shadows, and gives an unnaturally flat appearance. Since a few years, there are three-dimensional video systems available, but they have drawbacks considering image quality and comfort of use. In the SIMIC project 1 1 SIMIC project FKZ 16 SV 193 funded by the German Federal Ministry for Education and Research (BMBF). , the so-called “shadow telescope” 2 2 Developed and manufactured by Endoskopische Geräte Berlin (MGB), Rudower Chaussee 6, 12489 Berlin. with improved illumination has been developed. With the help of additional illumination fibres, a visible shadow and a more spatial and natural impression can be achieved. Comparative studies have been completed directly comparing two-dimensional (2-D) and three-dimensional (3-D) video systems. We also performed a study comparing the shadow telescope with conventional 2-D video. At the moment, a new study is proceeding comparing shadow vision with 3-D vision. The aim of this study using standardised phantom tasks is to gain objective information about benefits and drawbacks of shadow vision compared to 3-D vision. The results will be available and presented at the SMIT Congress 2001 in Berlin.