Uni-directional polymerization leading to homochirality in the RNA world

The differences between uni-directional and bi-directional polymerization are considered. The uni-directional case is discussed in the framework of the RNA world. Similar to earlier models of this type, where polymerization was assumed to proceed in a bi-directional fashion (presumed to be relevant to peptide nucleic acids), left-handed and right-handed monomers are produced via an autocatalysis from an achiral substrate. The details of the bifurcation from a racemic solution to a homochiral state of either handedness is shown to be remarkably independent of whether the polymerization in uni-directional or bi-directional. Slightly larger differences are seen when dissociation is allowed and the dissociation fragments are being recycled into the achiral substrate.Comment: 9 pages, 4 figures, submitted to Astrobiolog

Directional complexity and entropy for lift mappings

We introduce and study the notion of a directional complexity and entropy for maps of degree 1 on the circle. For piecewise affine Markov maps we use symbolic dynamics to relate this complexity to the symbolic complexity. We apply a combinatorial machinery to obtain exact formulas for the directional entropy, to find the maximal directional entropy, and to show that it equals the topological entropy of the map. Keywords: Rotation interval, Space-time window, Directional complexity, Directional entropy;Comment: 19p. 3 fig, Discrete and Continuous Dynamical Systems-B (Vol. 20, No. 10) December 201

Why do many animals move with a predominance of roughly forward directions?

Animal movements can influence their ecology and demographics. Animal movements are often characterized by path structures with directional persistence. The extent to which directional persistence improves forage success is investigated in this paper using theoretical simulations. It is shown that a movement strategy with directional persistence enables simulated animals to find more forage as compared to a random movement strategy. Situations where resources are chosen with certainty (optimally) are even more successful. Choosing resource with certainty cannot result in directional persistence. However, in cases where animals choose with certainty adjacent cells with resource but continue in their existing direction if none of these have resources then results include directional persistence. It is posited here that this combined strategy is the most effective because if optimal foraging works it is optimally efficient but where foraging is sub-optimal, for a variety of reasons, directional persistence will benefit foraging

Adaptive multi-channel MAC protocol for dense VANET with directional antennas

Directional antennas in Ad hoc networks offer more benefits than the traditional antennas with omni-directional mode. With directional antennas, it can increase the spatial reuse of the wireless channel. A higher gain of directional antennas makes terminals a further transmission range and fewer hops to the destination. This paper presents the design, implementation and simulation results of a multi-channel Medium Access Control (MAC) protocols for dense Vehicular Ad hoc Networks using directional antennas with local beam tables. Numeric results show that our protocol performs better than the existing multichannel protocols in vehicular environment

Differential Effects in Bimodal Directional Stroop Interference

The directional Stroop task (e.g., Cannon, 1998) creates interference between a directional word and a directional cue, such as an arrow. This study was conducted to replicate directional Stroop interference using bimodal stimulus pairs and then to determine whether or not interference occurs when the word is replaced with a sound. In Experiment 1, an arrow, pointing up or down, was paired with a directional word (UP or DOWN). Subjects were faster responding to the direction of the arrow when the pairs were congruent compared to incongruent indicating interference. In Experiment 2, the visual word was replaced with a voice. Incongruent trials produced longer RTs but there was no statistical difference between conditions. In Experiment 3, the auditory word was replaced with the sound of a slide whistle either going up or going down. Although response times were longer for incongruent pairs and the effect size was moderate, there was no significant interference between the arrow and a direction-related sound. Experiment 4 utilized the same design as Experiment 3. However, in Experiment 4 subjects responded to the direction of the sound instead of the arrow. Performance across conditions was virtually identical indicating that the visual directional cue (i.e., the arrow) had no impact on identifying the direction of the sound. Together, the results replicate previous research with a visual directional task but did not extend these findings to auditory-visual cross-modal tasks. However, the initial results from Experiments 3 and 4 suggest that auditory cues may influence visual directional cues but that visual cues do not influence auditory directional cues