Synthesizing antipodal chaotic waveforms

Chaotic waveforms are natural information carriers since a correspondence can be established between the symbolic dynamics of a chaotic oscillator and the symbols of a message. Message symbols can be efficiently encoded in a chaotic waveform by applying vanishingly small perturbations to an oscillator to guide its symbolic dynamics to follow a desired course. Recently, two chaotic hybrid dynamical systems were shown to have matched filters enabling robust reception of chaotic communication waveforms in the presence of noise. The first of these, the exact shift oscillator, produces waveforms with desirable properties similar to antipodal signaling, but a physical implementation may be difficult to control using small perturbations. The second oscillator, the exact folded-band oscillator, produces less optimal waveforms but is more easily controlled. Here we introduce a method for generating waveforms of the exact shift oscillator by summing waveforms from a bank of easily controlled exact folded-band oscillators. We show that any solution of the exact shift oscillator can be so constructed using only three folded-band oscillators. Thus, this scheme allows us to realize the advantages of both chaotic systems while overcoming their individual disadvantages, thereby enabling practical chaos communications.     

How persistent and general is the contextual interference effect?

The persistence and generality of the contextual interference (CI) effect was tested using a rapid sequential aiming task. Participants (N=48) practiced three movement patterns for three blocks of 18 trials under a blocked (BL) or random (RA) schedule. Movement patterns were displayed and KR provided throughout practice and testing. A 24-hr delayed knowledge of results (KR) retention test included three blocks of 18 trials, followed by a transfer test of a single new movement pattern. In contradiction of the CI effect, RA practice provided an advantage for RA retention only, not BL retention. Furthermore, group differences at transfer were not persistent. Hence, RA practice does not necessarily provide enhanced, context-free learning, but it is essential training for task switching. Overall the findings reveal limited persistence and generality of the CI effect.     

高效光伏电池

在没有阳光照亮的地方，请采用更好的背接触式太阳能电池。     

Footedness in world soccer: an analysis of France '98

Most football players and coaches agree that players are capable of learning to use both feet with equal frequency and efficiency – that is, become 'two-footed'. There is also some consensus that two-footed play is associated with skill in individual players. If these assumptions are true, then the world's elite football players should be substantially less 'one-footed' than the rest of the population. To examine this issue, we quantified the pattern of foot use in a sample of 236 players from 16 teams in the 1998 World Cup (France '98). Our findings indicate that World Cup players are as right-footed as the general population (~79%). The remaining players were largely leftfooted and as biased towards the use of their preferred foot as their right-footed counterparts. Very few players used each foot with equal frequency. Remarkably, both left- and right-footed players were as skilled, on average, with their non-preferred foot as they were with their preferred foot, on the rare occasions when they used it. Therefore, it is unlikely that infrequent use of one foot compared to the other foot can be accounted for by skill differences between the feet. Players were most asymmetrical for set pieces; nevertheless, first touches, passes, dribbles and tackles were rarely performed with the non-preferred foot as well. Our results support a biological model of foot preference and performance, as well as demonstrating the usefulness of soccer for studies of lateral asymmetries.