On-the-Fly Machine Learning of Atomic Potential in Density Functional Theory Structure Optimization.

Machine learning (ML) is used to derive local stability information for density functional theory calculations of systems in relation to the recently discovered SnO_{2}(110)-(4×1) reconstruction. The ML model is trained on (structure, total energy) relations collected during global minimum energy search runs with an evolutionary algorithm (EA). While being built, the ML model is used to guide the EA, thereby speeding up the overall rate by which the EA succeeds. Inspection of the local atomic potentials emerging from the model further shows chemically intuitive patterns.

Cis-interactions between Delta and Notch modulate neurogenic signalling in Drosophila.

We find that ectopic expression of Delta or Serrate in neurons within developing bristle organs is capable of non-autonomously inducing the transformation of the pre-trichogen cell into a tormogen cell in a wide variety of developmental contexts. The frequencies at which Delta can induce these transformations are dependent on the level of ectopic Delta expression and the levels of endogenous Notch signalling pathway components. The pre-trichogen cell becomes more responsive to Delta- or Serrate-mediated transformation when the level of endogenous Delta is reduced and less responsive when the dosage of endogenous Delta is increased, supporting the hypothesis that Delta interferes autonomously with the ability of a cell to receive either signal. We also find that a dominant-negative form of Notch, ECN, is capable of autonomously interfering with the ability of a cell to generate the Delta signal. When the region of Notch that mediates trans-interactions between Delta and the Notch extracellular domain is removed from ECN, the ability of Delta to signal is restored. Our findings imply that cell-autonomous interactions between Delta and Notch can affect the ability of a cell to generate and to transduce a Delta-mediated signal. Finally, we present evidence that the Fringe protein can interfere with Delta- and Serrate-mediated signalling within developing bristle organs, in contrast to previous reports of the converse effects of Fringe on Delta signalling in the developing wing.

Feedback regulation is central to Delta-Notch signalling required for Drosophila wing vein morphogenesis.

Delta and Notch are required for partitioning of vein and intervein cell fates within the provein during Drosophila metamorphosis. We find that partitioning of these fates is dependent on Delta-mediated signalling from 22 to 30 hours after puparium formation at 25 degrees C. Within the provein, Delta is expressed more highly in central provein cells (presumptive vein cells) and Notch is expressed more highly in lateral provein cells (presumptive intervein cells). Accumulation of Notch in presumptive intervein cells is dependent on Delta signalling activity in presumptive vein cells and constitutive Notch receptor activity represses Delta accumulation in presumptive vein cells. When Delta protein expression is elevated ectopically in presumptive intervein cells, complementary Delta and Notch expression patterns in provein cells are reversed, and vein loss occurs because central provein cells are unable to stably adopt the vein cell fate. Our findings imply that Delta-Notch signalling exerts feedback regulation on Delta and Notch expression during metamorphic wing vein development, and that the resultant asymmetries in Delta and Notch expression underlie the proper specification of vein and intervein cell fates within the provein.

Spatial perspective taking: coordination of left-right and near-far spatial dimensions.

Second- and fourth-grade children viewed a cylindrical object in nine positions on a square display board marked with a 3 X 3 grid. As the object was placed in each position children identified the view from 90, 180, or 270 degrees positions around the display from a set of photographs. Perspectives in which the object differed from the child's view in both left-right and near-far dimensions were more difficult than perspectives that only transformed one dimension. Error rates decreased with age. There were no main effects of left-right vs near-far or of observer position. Rates of egocentric responding were high at both ages. We note that the complementary spatial dimension to left-right is near-far not front-back. Moreover, the relative ease of front-back transformations in previous research resulted from distinctive front-back cues on the display objects which enabled subjects to use nonspatial strategies to identify observer perspectives.