Analytical reasoning task reveals limits of social learning in networks

Social learning—by observing and copying others—is a highly successful cultural mechanism for adaptation, outperforming individual information acquisition and experience. Here, we investigate social learning in the context of the uniquely human capacity for reflective, analytical reasoning. A hallmark of the human mind is its ability to engage analytical reasoning, and suppress false associative intuitions. Through a set of laboratory-based network experiments, we find that social learning fails to propagate this cognitive strategy. When people make false intuitive conclusions and are exposed to the analytic output of their peers, they recognize and adopt this correct output. But they fail to engage analytical reasoning in similar subsequent tasks. Thus, humans exhibit an ‘unreflective copying bias’, which limits their social learning to the output, rather than the process, of their peers’ reasoning—even when doing so requires minimal effort and no technical skill. In contrast to much recent work on observation-based social learning, which emphasizes the propagation of successful behaviour through copying, our findings identify a limit on the power of social networks in situations that require analytical reasoning.     

Antenna Array Designs for OFDM WLAN Indoor Transmission

Wireless local area networks (WLAN??s) based on the 802.11 standards are ubiquitous. However, the popularity of WLAN??s has made interference between WLAN users an issue. Spatial division multiple access (SDMA) is one way to orthogonalize these users and reduce interference. The contribution of this paper is to use real antenna array prototypes to determine the best array design for implementing indoor SDMA. Two SDMA antenna array prototypes are constructed and used to collect propagation measurements in an indoor environment. The propagation data is then incorporated into an SDMA orthogonal frequency division multiplexing (OFDM) analysis. This approach is able to very accurately predict how the two array designs will influence SDMA-OFDM performance in the indoor environment where the measurements are collected. The results indicate that the compact sectorized antenna array prototype performs better than the linear array prototype for in-room communication and that the reverse is true for inter-room communication.     

Adaptive multisensor receiver for mobile communications

This paper describes a digital receiver for radiomobile communications. The adaptive filter is a purely spatial filter. The used criterion is the minimisation of a mean square error between the array output signal and a reference signal. The reference signal is generated using the demodulator results. No learning sequence is required. The algorithm is digitally implemented and it uses a direct matrix inversion algorithm. The performance study, using simulation and experimental results, shows tracking properties, jammers cancelling and multivath correction.     

Deviation of a monochromatic Lamb wave beam in anisotropic multilayered media: asymptotic analysis, numerical and experimental results

The aim of this paper is threefold: to describe the physical phenomenon of the excitation of modal waves such as Lamb waves, in anisotropic multilayered media, by a monochromatic incident beam, using an asymptotic approach; to present a three-dimensional model using the decomposition of the incident beam into monochromatic plane waves (the formalism is applied to the particle displacement vector); to illustrate the phenomenon both numerically and experimentally. Numerical and experimental maps of the reflected field of pressure are presented, and the reradiation of the Lamb wave beam in an oblique plane is theoretically and numerically illustrated.     

Spatio-temporal coding in complex media for optimum beamforming: the iterative time-reversal approach

Spatio-temporal encoding in transmit and receive modes is of major importance in the development of ultrasound imaging devices. Classically, the assumption of constant sound speed in the medium allows one to restrict the beamforming process to the application of a cylindrical time-delay law on the elements of a multiple-transducer array. Here is proposed an iterative time-reversal method capable of taking into account all the heterogeneities of the medium, concerning density, speed of sound, and absorption variations. It will be shown that this iterative focusing process converges toward a spatio-temporal inverse filter focusing, the first step of the process being a time-reversal focusing on the targeted point. This method can be seen as a calibration process and has been successfully applied to transskull focusing and intraplate echoes suppression. It is leading the way to promising applications such as high-resolution ultrasonic brain imaging and high-resolution focusing through complex reverberating media, in nondestructive testing and telecommunications. This work highlights the advantages of using spatio-temporal coding to focus through complex media. Such codes require the use of fully programmable, multichannel electronics to implement this technique in real time.     

Symmetry Breaking Revisited

Symmetries in constraint satisfaction problems (CSPs) are one of the difficulties that practitioners have to deal with. We present in this paper a new method based on the symmetries of decisions taken from the root of the search tree. This method can be seen as an improvement of the SBDD method presented by Focacci and Milano [7] and Fahle, Schamberger and Sellmann [5]. We present a simple formalization of our method for which we prove correctness and completeness results. We show that our method is theoretically more efficient as the size of each no-good is smaller. This theoretical analysis is confirmed by thorough experimental evaluation on highly symmetrical real world problems. We are able to break all symmetries for problems with more than 10⁷⁸ symmetries.     

Comparison of eliminating first order samples for minimizing first serving order bias to data corrections

This study was conducted to investigate the impacts of eliminating first order samples and data corrections on overall liking (OL) results. Nine consumer studies were employed for this work. For each study, all first order products were eliminated from the data to examine the impacts of first order bias on OL. Significantly higher OL values were observed for products presented in first order for 6 of the 9 studies. After removing first order samples, OL for each product slightly decreased. In addition, slight changes in sample OL rank orders were observed for 8 of the 9 studies. Data sets with first position sample removed seemed less discriminative. This indicates that samples were discriminated to a greater extent due to first order bias and actual differences might be overstated. Two first order data corrections were successfully adapted to remedy the first order bias even after data were segmented by cluster analysis.     

In situ active chlorine generation for the treatment of dye-containing effluents

This study examined the possibility to remove colour causing-compounds from synthetic effluent by indirect electrochemical oxidation using iridium oxide anode electrodes. Using a high concentration of chloride ions (17.1 mM) and various current densities, it was possible to produce high concentration of active chlorine with a specific production rate of 2.8 mg min⁻¹ A⁻¹. The best performance for acid methyl violet 2B dye (MV2B) decomposition was obtained using Ti/IrO₂ anodes operated at a current density of 15 mA cm⁻² during 40 min of treatment in the presence of 3.42 mM of chloride ions. Under these conditions, more than 99% of MV2B was removed (with a reaction rate apparent constant of 0.20 min⁻¹), whereas COD and TOC removal were 51% and 75%, respectively. The electrolytic cell was then used for the degradation of three other synthetic dye solutions: Eosin yellowish (EOY), Trypan Blue (TRB), Acridine Orange (ACO). TRB was the most difficult dye to remove from solution with a value reaction rate constant of 0.12 min⁻¹, compared to 0.19 min⁻¹ and 0.24 min⁻¹ recorded for ACO and EOY dyes, respectively. More than 99% of these dyes were removed by electrochemical oxidation.     

EX vivo ESR measurements associated with Monte Carlo calculations for accident dosimetry: application to the 2001 Georgian accident

Electron spin resonance (ESR) spectroscopy and the Monte Carlo (MC) technique were jointly applied to the physical dose reconstruction of the accident that occurred on 2 December 2001 in Georgia. Three people were exposed to two very-high-activity (2.6 x 10(15) Bq) 90Sr sources. Following this exposure, the two most seriously affected victims exhibited severe radiological injuries localised in the back as well as a haematopoietic syndrome. The information concerning the circumstances of the accident in terms of sequences of irradiation and the exposure time was not clearly established. The physical dose reconstruction of the accident was performed for one victim, treated in France, using both MC simulations and ESR measurements made on one vertebra and two rib samples removed from the victim for medical reasons. The complementary nature of the two tools made it possible to estimate the dose distribution within the body with reasonable accuracy and helped to develop the treatment strategy.