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

Subdivision Directional Fields

We present a novel linear subdivision scheme for face-based tangent directional fields on triangle meshes. Our subdivision scheme is based on a novel coordinate-free representation of directional fields as halfedge-based scalar quantities, bridging the finite-element representation with discrete exterior calculus. By commuting with differential operators, our subdivision is structure-preserving: it reproduces curl-free fields precisely, and reproduces divergence-free fields in the weak sense. Moreover, our subdivision scheme directly extends to directional fields with several vectors per face by working on the branched covering space. Finally, we demonstrate how our scheme can be applied to directional-field design, advection, and robust earth mover's distance computation, for efficient and robust computation

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

Throughput sensitivity to antenna pattern and orientation in 802.11n networks

In this paper the throughput and packet error rate for an in-home 802.11n network is theoretically derived for two different types of 3x3 antenna configurations. Our first configuration assumes the use of three low directivity omni-dectional elements. The second arrangement makes use of three orthogonally orientated directional elements. The spatial and temporal characteristics of the in-home channels are modelled using 3D ray tracing and combined with appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is computed for all modulation and coding schemes using a received bit information rate abstraction technique. The theory shows that directional antennas outperform the omni-directional devices in most cases. Directional elements show increased sensitivity to orientation, however for 83% of locations and orientations they still result in throughput enhancement. Directional antennas provide a 33% improvement in average data rate for random client orientations, improving to 52% with optimum alignment to the multipath.In this paper the throughput and packet error rate for an in-home 802.11n network is theoretically derived for two different types of 3x3 antenna configurations. Our first configuration assumes the use of three low directivity omni-dectional elements. The second arrangement makes use of three orthogonally orientated directional elements. The spatial and temporal characteristics of the in-home channels are modelled using 3D ray tracing and combined with appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is computed for all modulation and coding schemes using a received bit information rate abstraction technique. The theory shows that directional antennas outperform the omni-directional devices in most cases. Directional elements show increased sensitivity to orientation, however for 83% of locations and orientations they still result in throughput enhancement. Directional antennas provide a 33% improvement in average data rate for random client orientations, improving to 52% with optimum alignment to the multipath

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

Testes asymmetry, condition and sexual selection in birds: an experimental test

The functional significance of the marked directional asymmetry in testes size observed in many bird species is obscure. Møller suggested that (i) the smaller of the two testes serves a compensatory role and increases in size (and hence reduces asymmetry) when the larger one is defective in some way, and (ii) as a consequence, the degree of directional asymmetry in testes size reflects male quality and covaries positively with the expression of secondary sexual traits.We conducted an experimental test of these two hypotheses in the zebra finch,Taeniopygia guttata. Neither hypothesis was supported. First, there was no significant relationship between the size of the left testis and relative testes asymmetry. Second, we obtained no support for the hypothesis that the degree of directional asymmetry in testes mass covaried with condition. On the contrary, directional asymmetry in testes mass was signifcantly greater in birds whose condition was experimentally reduced, compared with control birds. Moreover, we found no significant relationships between testes asymmetry and secondary sexual traits. We conclude that directional asymmetry in testes size does not reflect male condition in the zebra finch