Eye-tracking the emergence of attentional anchors in a mathematics learning tablet activity

Little is known about micro-processes by which sensorimotor interaction gives rise to conceptual development. Per embodiment theory, these micro-processes are mediated by dynamical attentional structures. Accordingly this study investigated eye-gaze behaviors during engagement in solving tablet-based bimanual manipulation tasks designed to foster proportional reasoning. Seventy-six elementary- and vocational-school students (9-15 yo) participated in individual task-based clinical interviews. Data gathered included action-logging, eye-tracking, and videography. Analyses revealed the emergence of stable eye-path gaze patterns contemporaneous with first enactments of effective manipulation and prior to verbal articulations of manipulation strategies. Characteristic gaze patterns included consistent or recurring attention to screen locations that bore non-salient stimuli or no stimuli at all yet bore invariant geometric relations to dynamical salient features. Arguably, this research validates empirically hypothetical constructs from constructivism, particularly reflective abstraction

Thermal X-Ray Pulses Resulting From Pulsar Glitches

The non-spherically symmetric transport equations and exact thermal evolution model are used to calculate the transient thermal response to pulsars. The three possible ways of energy release originated from glitches, namely the `shell', `ring' and `spot' cases are compared. The X-ray light curves resulting from the thermal response to the glitches are calculated. Only the `spot' case and the `ring' case are considered because the `shell' case does not produce significant modulative X-rays. The magnetic field ($\vec B$) effect, the relativistic light bending effect and the rotational effect on the photons being emitted in a finite region are considered. Various sets of parameters result in different evolution patterns of light curves. We find that this modulated thermal X-ray radiation resulting from glitches may provide some useful constraints on glitch models.Comment: 48 pages, 20 figures, submitted to Ap

Thomas-Fermi Calculations of Atoms and Matter in Magnetic Neutron Stars II: Finite Temperature Effects

We present numerical calculations of the equation of state for dense matter in high magnetic fields, using a temperature dependent Thomas-Fermi theory with a magnetic field that takes all Landau levels into account. Free energies for atoms and matter are also calculated as well as profiles of the electron density as a function of distance from the atomic nucleus for representative values of the magnetic field strength, total matter density, and temperature. The Landau shell structure, which is so prominent in cold dense matter in high magnetic fields, is still clearly present at finite temperature as long as it is less than approximately one tenth of the cyclotron energy. This structure is reflected in an oscillatory behaviour of the equation of state and other thermodynamic properties of dense matter and hence also in profiles of the density and pressure as functions of depth in the surface layers of magnetic neutron stars. These oscillations are completely smoothed out by thermal effects at temperatures of the order of the cyclotron energy or higher.Comment: 37 pages, 17 figures included, submitted to Ap

Praktische opdrachten bij Grieks en Latijn

Dit is een Ico-Isor rappor

Influence of hydrodynamic interactions on the ballistic deposition of colloidal particles on solid surfaces

The ballistic deposition of particles by taking hydrodynamic interactions (HI) into account has been studied by means of computer simulations. The radial distribution function of the assembly of particles deposited on a plane has been determined as a function of the coverage and compared to experimental data. It appears that the introduction of HI in the model when compared to the ballistic model predictions leads to a better agreement between experiment and simulation in particular for the radial distribution function.Comment: 13 pages To appear in Journal of Chemical Physics. 8 figures available upon reques

Temperature distribution in magnetized neutron star crusts

We investigate the influence of different magnetic field configurations on the temperature distribution in neutron star crusts. We consider axisymmetric dipolar fields which are either restricted to the stellar crust, ``crustal fields'', or allowed to penetrate the core, ``core fields''. By integrating the two-dimensional heat transport equation in the crust, taking into account the classical (Larmor) anisotropy of the heat conductivity, we obtain the crustal temperature distribution, assuming an isothermal core. Including quantum magnetic field effects in the envelope as a boundary condition, we deduce the corresponding surface temperature distributions. We find that core fields result in practically isothermal crusts unless the surface field strength is well above $10^{15}$ G while for crustal fields with surface strength above a few times $10^{12}$ G significant deviations from isothermality occur at core temperatures inferior or equal to $10^8$ K. At the stellar surface, the cold equatorial region produced by the quantum suppression of heat transport perpendicular to the field in the envelope, present for both core and crustal fields, is significantly extended by the classical suppression at higher densities in the case of crustal fields. This can result, for crustal fields, in two small warm polar regions which will have observational consequences: the neutron star has a small effective thermally emitting area and the X-ray pulse profiles are expected to have a distinctively different shape compared to the case of a neutron star with a core field. These features, when compared with X-ray data on thermal emission of young cooling neutron stars, will open a way to provide observational evidence in favor, or against, the two radically different configurations of crustal or core magnetic fields.Comment: 10 pages, 10 figures, submitted to A&

Innovations in ground and airborne technologies as reference and for training and validation : terrestrial laser scanning (TLS)

The use of terrestrial laser scanning (TLS) to provide accurate estimates of 3D forest canopy structure and above-ground biomass (AGB) has developed rapidly. Here, we provide an overview of the state of the art in using TLS for estimating forest structure for AGB. We provide a general overview of TLS methods and then outline the advantages and limitations of TLS for estimating AGB. We discuss the specific type of measurements that TLS can provide, tools and methods that have been developed for turning TLS point clouds into quantifiable metrics of tree size and volume, as well as some of the challenges to improving these measurements. We discuss the role of TLS for enabling accurate calibration and validation (cal/val) of Earth observation (EO)-derived estimates of AGB from spaceborne lidar and RADAR missions. We give examples of the types of TLS equipment that are in use and how these might develop in future, and we show examples of where TLS has already been applied to measuring AGB in the tropics in particular. Comparing TLS with harvested AGB shows r(2)>0.95 for all studies thus far, with absolute agreement to within 10% at the individual tree level for all trees and to within 2% in the majority of cases. Current limitations to the uptake of TLS include the capital cost of some TLS equipment, processing complexity and the relatively small coverage that is possible. We argue that combining TLS measurements with the existing ground-based survey approaches will allow improved allometric models and better cal/val, resulting in improved regional and global estimates of AGB from space, with better-characterised, lower uncertainties. The development of new, improved equipment and methods will accelerate this process and make TLS more accessible

New cooperative effects in ballistic deposition of hard disks

In this Letter, we analyze the problem of monolayer formation onto a flat surface by deposition of hard particles. Our detailed computer simulations of ballistic deposition of hard disks show significant deviations from the classical analytical solution obtained by J. Talbot et al. [Phys. Rev. Lett. 68, 958 (1992)]. These deviations are due to cooperative adsorption induced by particles trapped above the adsorbed layer. We show that not only the adsorption kinetics but also the jamming (saturation) coverage of the surface depends on the volume fraction of the suspension, a prediction which is completely new. These new cooperative effects cannot be neglected even in the case of very diluted suspensions

Adsorption of colloidal particles in the presence of external field

We present a new class of sequential adsorption models in which the adsorbing particles reach the surface following an inclined direction (shadow models). Capillary electrophoresis, adsorption in the presence of a shear or on an inclined substrate are physical manifestations of these models. Numerical simulations are carried out to show how the new adsorption mechanisms are responsible for the formation of more ordered adsorbed layers and have important implications in the kinetics, in particular modifying the jamming limit.Comment: LaTex file, 3 figures available upon request, to appear in Phys.Rev.Let