Interdigitated back‐contact heterojunction solar cell concept for liquid phase crystallized thin‐film silicon on glass

We present an interdigitated back‐contact silicon heterojunction system designed for liquid‐phase crystallized thin‐film (~10 µm) silicon on glass. The preparation of the interdigitated emitter (a‐Si:H(p)) and absorber (a‐Si:H(n)) contact layers relies on the etch selectivity of doped amorphous silicon layers in alkaline solutions. The etch rates of a‐Si:H(n) and a‐Si:H(p) in 0.6% NaOH were determined and interdigitated back‐contact silicon heterojunction solar cells with two different metallizations, namely Al and ITO/Ag electrodes, were evaluated regarding electrical and optical properties. An additional random pyramid texture on the back side provides short‐circuit current density (j_SC) of up to 30.3 mA/cm² using the ITO/Ag metallization. The maximum efficiency of 10.5% is mainly limited by a low of fill factor of 57%. However, the high j_SC, as well as V_OC values of 633 mV and pseudo‐fill factors of 77%, underline the high potential of this approach. Copyright © 2015 John Wiley & Sons, Ltd.     

Spatiotemporal EEG/MEG source analysis based on a parametric noise covariance model

A method is described to incorporate the spatiotemporal noise covariance matrix into a spatiotemporal source analysis. The essential feature is that the estimation problem is split into two parts. First, a model is fitted to the observed noise covariance matrix. This model is a Kronecker product of a spatial and a temporal matrix. The spatial matrix models the spatial covariances by a function dependent on sensor distance. The temporal matrix models the temporal covariances as lag dependent. In the second part, sources are estimated given this noise model, which can be done very efficiently due to the Kronecker formulation. An application to real electroencephalogram (EEG) data shows that the noise model fits the data very well. Simulation results show that the resulting source estimates are more precise than those obtained from a standard analysis neglecting the noise covariance. In addition, the estimated standard errors of the source parameter estimates are far more precise than those obtained from a standard analysis. Finally, the source parameter standard errors are used to investigate the effects of temporal sampling. It is shown that increasing the sampling by a factor x, decreases the standard errors of all source parameters with the square root of x.     

Power and Speed-Efficient Code Transformation of Video Compression Algorithms for RISC Processors

Upcoming multi-media compression applications will require high memory bandwidth. In this paper, we estimate that a software reference implementation of an MPEG-4 video decoder typically requires 200 Mtransfers/s to memory to decode 1 CIF (352×288) Video Object Plane (VOP) at 30 frames/s. This imposes a high penalty in terms of power but also performance.However, we also show that we can heavily improve on the memory transfers, without sacrificing speed (even gaining about 10% on cache misses and cycles for a DEC Alpha), by aggressive code transformations. For this purpose, we have manually applied an extended version of our data transfer and storage exploration (DTSE) methodology, which was originally developed for custom hardware implementations.     

A subspace matching color filter design methodology for a multispectral imaging system.

In this paper, we present a methodology to design filters for an imaging system to improve the accuracy of the spectral measurements for families of reflective surfaces. We derive the necessary and sufficient conditions that the sensor space of the system must obey in order to measure the spectral reflectance of the surfaces accurately. Through simulations, we show how these conditions can be applied to design filters using a set of sample spectral data acquired from extracted teeth. For this set of data, we also compare our results to those of Wolski's method, a conventional filter design method which produces filters that recover tristimulus values of surfaces accurately under several illuminants. We show that our method produces filters that capture the spectral reflectance better given the same number of measurements. The errors in predicting the color of the sample data are much lower under every test illuminant when the filters designed with our method are used.     

Increasing inequalities in what we do online: A longitudinal cross sectional analysis of Internet activities among the Dutch population (2010 to 2013) over gender,age, education,and income

We investigate types of Internet activities among a representative sample of the Dutch population from 2010 to 2013. We examined usage patterns of seven types of Internet activities (i.e., information, news, personal development, commercial transaction, social interaction, leisure, and gaming) and related these patterns with gender, age, education, and income. Activities related to news, personal development, commercial transaction, and social interaction increased in popularity. For most capital enhancing activities, men, younger people, higher educated people, and people with higher than average incomes were prominent. These observations, however, are subject to change. The Internet seems to provide increasingly more capital-enhancing opportunities for those with higher education and income, which would accordingly reinforce their already strong positions in society.     

Energy-efficient Rate Adaptation MAC Protocol for Ad Hoc Wireless Networks

In this paper, two novel energy-efficient rate adaptation schemes are presented. The proposed protocols use the Distributed Power Control (DPC) algorithm to predict the channel state and determine the necessary transmission power which optimizes the energy consumption. The first proposed rate adaptation scheme heuristically alters the modulation rate to balance the energy-efficiency and the required throughput which is estimated with queue fill ratio. Moreover, the back-off scheme is incorporated to mitigate congestion and reduce packet losses due to buffer overflows thus minimizing energy consumption. Consequently, the nodes will conserve energy when the traffic is low, offer higher throughput when needed and save energy during congestion by limiting transmission rates. The second rate adaptation scheme employs dynamic programming (DP) principle to analytically select modulation rate and a burst size to be used during transmission. The proposed quadratic cost-function minimizes the energy consumption while alleviating network congestions and buffer overflows. The proposed DP solution renders a Riccati equation ultimately providing an optimal rate selection. The simulation results indicate that an increase in throughput by 96% and energy-efficiency by 131% is observed when compared to other available protocols, for example Receiver Based AutoRate (RBAR).

Optical determination of the junction temperature of OLEDs

This paper describes a novel optical measurement technique for the in situ determination of the spatial temperature distribution at the organic layer level in large-area organic light-emitting diodes (OLEDs). The local junction temperature of OLEDs is a very important factor with respect to the luminance uniformity. Moreover the variation of local temperatures leads to a non-uniform depreciation of its light output, which in turn increases the luminance non-uniformity over time and affects the lifetime expectancy of the OLED.     

Multidimensional Nonlinear Schur Parametrization of NonGaussian Stochastic Signals. Part One: Statement of the Problem

The subject of this three-part paper is the multidimensional nonlinear Schur parametrization problem for higher-order (and non-Gaussian) stochastic signals. In the first part of this paper we state the nonlinear orthogonal parametrization problem as a generalization of the linear prediction/innovations filter problem. A unified geometric approach to the problem is introduced in the following three isometrically isomorphic spaces: of random variables (of higher-order stochastic sequences), of multi-indexed matrices, and of multidimensional z-polynomials. The nonlinear orthogonal approximate filters of the Volterra–Wiener class are considered. In the second part [30] of this paper we derive a generalized multidimensional nonlinear Schur parametrization algorithm for higher-order nonstationary stochastic sequences. The third part [33] of the paper is devoted to the complexity reduction problem in the nonlinear case, where a low-complexity Schur parametrization procedure, following from a nonlinear generalization of the staircase matrix extension problem [13], is proposed.     

Learning about learning: patterns of sharing of research knowledge among Education,Border, and Cognitive Science fields

This study explores the patterns of exchange of research knowledge among Education Research, Cognitive Science, and what we call “Border Fields.” We analyze a set of 32,121 articles from 177 selected journals, drawn from five sample years between 1994 and 2014. We profile the references that those articles cite, and the papers that cite them. We characterize connections among the fields in sources indexed by Web of Science (WoS) (e.g., peer-reviewed journal articles and proceedings), and connections in sources that are not (e.g., conference talks, chapters, books, and reports). We note five findings—first, over time the percentage of Education Research papers that extensively cite Cognitive Science has increased, but the reverse is not true. Second, a high percentage of Border Field papers extensively cite and are cited by the other fields. Border Field authors’ most cited papers overlap those most cited by Education Research and Cognitive Science. There are fewer commonalities between Educational research and Cognitive Science most cited papers. This is consistent with Border Fields being a bridge between fields. Third, over time the Border Fields have moved closer to Education Research than to Cognitive Science, and their publications increasingly cite, and are cited by, other Border Field publications. Fourth, Education Research is especially strongly represented in the literature published outside those WoS-indexed publications. Fifth, the rough patterns observed among these three fields when using a more restricted dataset drawn from the WoS are similar to those observed with the dataset lying outside the WoS, but Education Research shows a far heavier influence than would be indicated by looking at WoS records alone.