Unwanted Illumination Research Articles

Methodology and Error Analysis of Direct Resistance Measurements Used for the Quantification of Boron–Hydrogen Pairs in Crystalline Silicon

A method for quantifying dopant–hydrogen pairs and their formation dynamics in crystalline silicon by means of directly contacted resistance measurements is presented and exemplarily validated. The method can also be applied in-situ in the temperature range where dopant–hydrogen pair formation occurs. Furthermore, the influence of different confounding factors such as a faulty assumption of doping level, unnoticed temperature variations, and unwanted illumination is quantified. It is concluded that the detection limit of dopant–hydrogen pairs of the presented method is most likely limited by unnoticed temperature fluctuations and scales with the actual dopant concentration. For crystalline silicon doped with 1016 cm−3 as it is usually used for photovoltaic applications, the detection limit is found to be below 1013 cm−3.

Using geometric constraints to improve performance of image classifiers for automatic segmentation of traffic signs

Automatic detection and recognition of traffic signs from images is an important topic in many applications. At first, we segmented the images using a classification algorithm to delineate the areas where the signs are more likely to be found. In this regard, shadows, objects having similar colours, and extreme illumination changes can significantly affect the segmentation results. We propose a new shape-based algorithm to improve the accuracy of the segmentation. The algorithm works by incorporating the sign geometry to filter out the wrong pixels from the classification results. We performed several tests to compare the performance of our algorithm against those obtained by popular techniques such as Support Vector Machine (SVM), K-Means, and K-Nearest Neighbours. In these tests, to overcome the unwanted illumination effects, the images are transformed into colour spaces Hue, Saturation, and Intensity, YUV, normalized red green blue, and Gaussian. Among the traditional techniques used in this study, the best results were obtained with SVM applied to the images transformed into the Gaussian colour space. The comparison results also suggested that by adding the geometric constraints proposed in this study, the quality of sign image segmentation is improved by 10%–25%. We also comparted the SVM classifier enhanced by incorporating the geometry of signs with a U-Shaped deep learning algorithm. Results suggested the performance of both techniques is very close. Perhaps the deep learning results could be improved if a more comprehensive data set is provided.

Utilising variable sorting for normalisation to correct illumination effects in close-range spectral images of potato plants

Visible and near-infrared spectral imaging is a key non-destructive technique for rapid assessment of biophysical traits of plants. A major challenge with close-range spectral imaging of plants is spectral variation arising from illumination effects, which may mask the signals due to physiochemical differences. In the present work, we describe a new scatter correction technique called variable sorting for normalisation (VSN) and compare its efficiency with that of the commonly used standard normal variate (SNV) technique for the removal of unwanted illumination effects. Spectral images of potato plants were used for testing the correction. The results showed that the VSN outperformed SNV in removing illumination effects from the images of plants. The results show that the VSN approach to illumination correction can support high-throughput plant phenotyping where spectral imaging is used as a continuous monitoring tool.

Artifacts in time-resolved Kelvin probe force microscopy.

Kelvin probe force microscopy (KPFM) has been used for the characterization of metals, insulators, and semiconducting materials on the nanometer scale. Especially in semiconductors, the charge dynamics are of high interest. Recently, several techniques for time-resolved measurements with time resolution down to picoseconds have been developed, many times using a modulated excitation signal, e.g., light modulation or bias modulation that induces changes in the charge carrier distribution. For fast modulation frequencies, the KPFM controller measures an average surface potential, which contains information about the involved charge carrier dynamics. Here, we show that such measurements are prone to artifacts due to frequency mixing, by performing numerical dynamics simulations of the cantilever oscillation in KPFM subjected to a bias-modulated signal. For square bias pulses, the resulting time-dependent electrostatic forces are very complex and result in intricate mixing of frequencies that may, in some cases, have a component at the detection frequency, leading to falsified KPFM measurements. Additionally, we performed fast Fourier transform (FFT) analyses that match the results of the numerical dynamics simulations. Small differences are observed that can be attributed to transients and higher-order Fourier components, as a consequence of the intricate nature of the cantilever driving forces. These results are corroborated by experimental measurements on a model system. In the experimental case, additional artifacts are observed due to constructive or destructive interference of the bias modulation with the cantilever oscillation. Also, in the case of light modulation, we demonstrate artifacts due to unwanted illumination of the photodetector of the beam deflection detection system. Finally, guidelines for avoiding such artifacts are given.

Daylight Optimization for Green Office Building: A Study of West Facing Window Design and Configuration

Window placement and shading device configuration plays an important role when designing with daylight. In the tropical context, windows-especially on the west facade, can create unwanted illumination and induce glare. Excessive interior lighting can cause discomfort and stress amongst the users while poorly lit areas can have physical and mental consequences. Thus, the openings are to be configured as such that the interior can be naturally-lit while providing the optimum lighting for the required activities. In order to design a naturally-lit green office building, an experiment was conducted to determine the best opening configuration of a north-west facing building. For this purpose, a study model was constructed with adjustable slot-in louvres on the western side. A lux meter was used to measure the illuminance of the interior for different configurations of windows which varied according to the spacing, position, material and number of louvres. The daylight factor was calculated and the findings were found to be consistent with other literature on this topic. The results were established for several configurations which could be incorporated into design according to the design requirements. Finally, the findings were adapted and adjusted with respect to the building context and surroundings in designing the shading device for a green office building.

An Effective Face Recognition in Various Lighting Conditions Using LBP/LTP Techniques

Making recognition is more reliable under uncontrolled lighting conditions is one of the most important challenges for practical face recognition systems. We tackle this by combining following methods. The first step is simple and efficient preprocessing chain. The preprocessing is used to avoid the unwanted illumination effects such as Non-uniform illumination, Shadowing & highlights, aliasing, blurring and noise. Second step includes local binary pattern (LBP) and local ternary pattern methods (LTP). LBP is possible to describe the texture and shape of a digital image. LTP is a generalization of the local binary pattern (LBP). Local texture descriptor that is more discriminant and less sensitive to noise in uniform regions. The final step is used to improve robustness by adding two complementary sources Gabor wavelets and LBP showing that the combination is considerably more accurate than either feature set alone.

ON THE HARDNESS OF THE BORDER LENGTH MINIMIZATION PROBLEM ON A RECTANGULAR ARRAY

DNA microarray technology has proven to be an invaluable tool for molecular biologists. Microarrays are used extensively in SNP detection, genomic hybridization, alternative splicing and gene expression profiling. However the manufacturers of the microarrays are often stuck with the problem of minimizing the effects of unwanted illumination (border length minimization (BLM)) which is a hard combinatorial problem. In this paper we prove that the BLM problem on a rectangular grid is NP-hard – this however does not mean the BLM problem on a square grid is NP-hard. We also give the first integer linear programming (ILP) formulation to solve BLM problem optimally. Experimental results indicate that our ILP method produces superior results (both in runtime and cost) compared to the current state of the art algorithms to solve the BLM problem optimally.

Experimental quality factor determination of guided-mode resonances in photonic crystal slabs

We report on a method how quality factors of guided-mode resonances in photonic crystal slabs (PCSs) can be determined in the reciprocal space. Transmission measurements through PCSs are performed using crossed polarization filters before and after the PCS. Consequently the unwanted illumination source is suppressed and only the guided-mode resonances are revealed. This method allows for a spatially resolved quality factor determination in the reciprocal space. As an example we scan a two-dimensional PCS and visualize its inhomogeneities. Although the resonance wavelength variations were only ≈3 nm, the quality factor varies from 100 to 350.

Probability of a Laser Illuminating a Space Object

Laser beam impingement probability is needed to quantify the risk of accidental or unwanted illumination of a spaceobject.Atheoreticalmethodofcombininglaserbeampointingerrorandspaceobjectposition errorisused to calculatebeam impingementprobability.Themethodaccountsforposition,velocity,anderrorcovariancematrices of laser emitter and space object. Laser slew rate, pointing uncertainty, and beam divergence half-cone angle, as well asspace object sizeand shape, arealso included in the formulation. In performing thecalculation, parameters are transformed to a laser beam coordinated frame that is centered on the nominal beam axis. Instantaneous and time-dependent impingement probabilities are reduced to one-dimensional contour integrals. The cumulative impingement probability is expressed as a simple integral. A software tool was created to implement the method. Numerical results for example data are presented. Nomenclature A = unit vector normal to the laser beam having the largest pointing uncertainty a = standard deviation of the symmetric probability density,m B§ = y-axis intercept parameter in the diagonal frame, m b = standard deviation along the y axis of the diagonal frame, m C = satellite and laser combined error covariance matrix

Collection Efficiencies Greater Than Unity by Electron Or Hole Gating in a-Si:H p-i-n Diodes

AbstractWe report measured electron and hole gating in thick a-Si:H (3.5 μm) p-i-n diodes under reverse bias conditions. Previous publications have shown very high collection efficiency values for electron gating (p-side bias, n-side probe) of up to 50 (i.e. 5000%) for measured and simulated data and predictions of up to 400 (i.e. 40000%) from simulations. Reversing the usual sides of illumination for (electron) gating a situation can be created where, by n-side bias and p-side probe illumination, holes can be gated to travel through the sample to be collected at the contact. Even though the holes have much lower mobility, by this process we can still obtain collection efficiencies greater than unity. This measurement is more difficult because of unwanted illumination by stray bias beam photons on the more sensitive p-side, caused by reflections within the apparatus. Simulation of this situation corroborates qualitatively the measured data. A wide ranging study of the gating phenomenon in relation to different incident wavelengths and photon fluxes for bias and probe beam is reported. We present comparisons of electron and hole gating by measurement and simulation and explain the phenomenon for both electron and hole gating in terms of field changes near to the incident bias interface.