Investigation of deep flaws in thin walled tanks

Growth of deep surface flaws in thin wall tanks of aluminum and titanium base metal

On Bit-loading for Discrete Multi-tone Transmission over Short Range POF Systems

International audienceA novel bit-loading approach is proposed for the discrete multi-tone (DMT) transmission over short range polymer optical fiber (POF) systems. First of all, from the extract signal-to-noise ratio (SNR) table of quadrature amplitude modulation (QAM) for different desired bit error rates (BER), a new linear approximation (LA) expression is introduced to implement bit-loading for DMT systems. Then, based on water-filling concept, the performance bounds and optimal power allocations for the classical and the proposed bit-loading algorithms in Gaussian low-pass channel models are derived. Consequently, introducing the measured channel parameters of step-index (SI)-POF channels with different transmission distances, the theoretical performance bounds are computed and the practical transmission rates are simulated. Simulation results show that the proposed LA expression based bit-loading achieves higher transmission rate than classical modulation gap based bit-loading. Both algorithms use sub-optimal Chow algorithm with constant power allocation and iterative process. Finally, real DMT transmissions over SI-POFs are implemented in order to verify the proposed method. The LA expression based bit-loading outperforms the modulation gap based bit-loading in DMT transmission systems over different transmission distances. Moreover, experimental results show that the longer fiber length, the higher performance gain with LA expression based bit-loading. In the comparisons, for a 50 m SI-POF transmission, the transmission rate in DMT system with LA expression based bit-loading is improved by 5 % with the same experimental setups for a given BER at 1e-3 and by 10% for a 100 m length

Neuronal oscillations reveal the processes underlying intentional compared to incidental learning in children and young adults

This EEG study investigated the neuronal processes during intentional compared to incidental learning in young adults and two groups of children aged 10 and 7 years. Theta (3–8 Hz) and alpha (10–16 Hz) neuronal oscillations were analyzed to compare encoding processes during an intentional and an incidental encoding task. In all three age groups, both encoding conditions were associated with an increase in event-related theta activity. Encoding-related alpha suppression increased with age. Memory performance was higher in the intentional compared to the incidental task in all age groups. Furthermore, intentional learning was associated with an improved encoding of perceptual features, which were relevant for the retrieval phase. Theta activity increased from incidental to intentional encoding. Specifically, frontal theta increased in all age groups, while parietal theta increased only in adults and older children. In younger children, parietal theta was similarly high in both encoding phases. While alpha suppression may reflect semantic processes during encoding, increased theta activity during intentional encoding may indicate perceptual binding processes, in accordance with the demands of the encoding task. Higher encoding-related alpha suppression in the older age groups, together with age differences in parietal theta activity during incidental learning in young children, is in line with recent theoretical accounts, emphasizing the role of perceptual processes in mnemonic processing in young children, whereas semantic encoding processes continue to mature throughout middle childhood

Optimized Discrete Multitone Communication Over Polymer Optical Fiber

International audienceIn this paper, we propose an overall optimization of discrete multitone (DMT) transmissions over polymer optical fiber (POF). The optimization is carried out from both a theoretical and experimental approach. At first, the parameters of the POF channel characteristics, resonant cavity light emitting diode (RC-LED) dynamic nonlinearity performance and analog-to-digital converter effective number of bits (ENOB), in our digital storage oscilloscope are measured. From the measured results, we investigate the channel capacity of a 50 m step-index POF system. Then the optimal DMT bandwidth is theoretically derived. We also optimize the system with different experimental setups. The optimal cyclic prefix length and RC-LED optimal working current are given. The ENOB can be improved by oversampling and averaging. The optimal oversampling factor is discussed. Furthermore, a joint DMT clipping and subcarrier number optimization is synthetically investigated. Based on the proposed approaches, an optimized DMT gigabit transmission over a real 50 m POF channel employing low-cost components is presented. Finally, a methodology for the practical design of the DMT transmission over POF is concluded

Auto-SOM: recursive parameter estimation for guidance of self-organizing feature maps

An important technique for exploratory data analysis is to forma mapping from the high-dimensional data space to a low-dimensional representation space such that neighborhoods are preserved. A popular method for achieving this is Kohonen's self-organizing map (SOM) algorithm. However, in its original form, this requires the user to choose the values of several parameters heuristically to achieve good performance. Here we present the Auto-SOM, an algorithm that estimates the learning parameters during the training of SOMs automatically. The application of Auto-SOM provides the facility to avoid neighborhood violations up to a user-defined degree in either mapping direction. Auto-SOM consists of a Kalman filter implementation of the SOM coupled with a recursive parameter estimation method. The Kalman filter trains the neurons' weights with estimated learning coefficients so as to minimize the variance of the estimation error. The recursive parameter estimation method estimates the width of the neighborhood function by minimizing the prediction error variance of the Kalman filter. In addition, the "topographic function" is incorporated to measure neighborhood violations and prevent the map's converging to configurations with neighborhood violations. It is demonstrated that neighborhoods can be preserved in both mapping directions as desired for dimension-reducing applications. The development of neighborhood-preserving maps and their convergence behavior is demonstrated by three examples accounting for the basic applications of self-organizing feature maps

1.5 Gbps PN-ZP-DMT Transmission System for 1-mm Core Diameter SI-POF with RC-LED

A novel PN-ZP-DMT transmission scheme without requiring dedicated pilots for channel estimation is proposed. Hardware experiments on 50 m SI-POF with RC-LED show that the proposed scheme achieves a transmission rate of 1.5 Gbps with low cost off the shelf components