2,630 research outputs found
Teacher and child talk in active learning and whole-class contexts : some implications for children from economically less advantaged home backgrounds
This paper reports the experiences of 150 children and six primary teachers when active learning pedagogies were introduced into the first year of primary schools. Although active learning increased the amount of talk between children, those from socio-economically advantaged homes talked more than those from less advantaged homes. Also, individual children experienced very little time engaged in high-quality talk with the teacher, despite the teachers spending over one-third of their time responding to children's needs and interests. Contextual differences, such as the different staffing ratios in schools and pre-schools,may affect how well the benefits of active learning transfer from preschool contexts into primary schools. Policy-makers and teachers should pay particular attention to the implications of this for the education of children from economically less advantaged home backgrounds
A synthetic environment for visualization and planning of orbital maneuvers
An interactive proximity operations planning system, which allows on-site planning of fuel-efficient, multi-burn maneuvers in a potential multi-space-craft environment has been developed and tested. This display system most directly assists planning by providing visual feedback in a synthetic virtual space that aids visualization of trajectories and their constraints. Its most significant features include (1) an 'inverse dynamics' algorithm that removes control nonlinearities facing the operator and (2) a stack-oriented action-editor that reduces the order of control and creates, through a 'geometric spreadsheet,' the illusion of an inertially stable environment. This synthetic environment provides the user with control of relevant static and dynamic properties of way-points during small orbital changes allowing independent solutions to otherwise coupled problems of orbital maneuvering
Interactive orbital proximity operations planning system
An interactive, graphical proximity operations planning system was developed which allows on-site design of efficient, complex, multiburn maneuvers in the dynamic multispacecraft environment about the space station. Maneuvering takes place in, as well as out of, the orbital plane. The difficulty in planning such missions results from the unusual and counterintuitive character of relative orbital motion trajectories and complex operational constraints, which are both time varying and highly dependent on the mission scenario. This difficulty is greatly overcome by visualizing the relative trajectories and the relative constraints in an easily interpretable, graphical format, which provides the operator with immediate feedback on design actions. The display shows a perspective bird's-eye view of the space station and co-orbiting spacecraft on the background of the station's orbital plane. The operator has control over two modes of operation: (1) a viewing system mode, which enables him or her to explore the spatial situation about the space station and thus choose and frame in on areas of interest; and (2) a trajectory design mode, which allows the interactive editing of a series of way-points and maneuvering burns to obtain a trajectory which complies with all operational constraints. Through a graphical interactive process, the operator will continue to modify the trajectory design until all operational constraints are met. The effectiveness of this display format in complex trajectory design is presently being evaluated in an ongoing experimental program
Exocentric direction judgements in computer-generated displays and actual scenes
One of the most remarkable perceptual properties of common experience is that the perceived shapes of known objects are constant despite movements about them which transform their projections on the retina. This perceptual ability is one aspect of shape constancy (Thouless, 1931; Metzger, 1953; Borresen and Lichte, 1962). It requires that the viewer be able to sense and discount his or her relative position and orientation with respect to a viewed object. This discounting of relative position may be derived directly from the ranging information provided from stereopsis, from motion parallax, from vestibularly sensed rotation and translation, or from corollary information associated with voluntary movement. It is argued that: (1) errors in exocentric judgements of the azimuth of a target generated on an electronic perspective display are not viewpoint-independent, but are influenced by the specific geometry of their perspective projection; (2) elimination of binocular conflict by replacing electronic displays with actual scenes eliminates a previously reported equidistance tendency in azimuth error, but the viewpoint dependence remains; (3) the pattern of exocentrically judged azimuth error in real scenes viewed with a viewing direction depressed 22 deg and rotated + or - 22 deg with respect to a reference direction could not be explained by overestimation of the depression angle, i.e., a slant overestimation
A trajectory planning scheme for spacecraft in the space station environment
Simulated annealing is used to solve a minimum fuel trajectory problem in the space station environment. The environment is special because the space station will define a multivehicle environment in space. The optimization surface is a complex nonlinear function of the initial conditions of the chase and target crafts. Small permutations in the input conditions can result in abrupt changes to the optimization surface. Since no prior knowledge about the number or location of local minima on the surface is available, the optimization must be capable of functioning on a multimodal surface. It was reported in the literature that the simulated annealing algorithm is more effective on such surfaces than descent techniques using random starting points. The simulated annealing optimization was found to be capable of identifying a minimum fuel, two-burn trajectory subject to four constraints which are integrated into the optimization using a barrier method. The computations required to solve the optimization are fast enough that missions could be planned on board the space station. Potential applications for on board planning of missions are numerous. Future research topics may include optimal planning of multi-waypoint maneuvers using a knowledge base to guide the optimization, and a study aimed at developing robust annealing schedules for potential on board missions
The status of traditional Scottish animal breeds and plant varieties and the implications for biodiversity
The aim of this scoping study was to evaluate the effects on Scottish biodiversity of
changes in the use of traditional breeds and varieties. The overall objectives were:
a) The evaluation of the importance of genetic loss from the reduction in use of these
breeds and varieties, for example, the loss of unusual characteristics that might have
been of particular local use.
b) An assessment of the impacts of reduction in the ability to conduct further breeding or
research on rare and traditional varieties and breeds.
c) Identification of the loss of certain farming techniques associated with particular
varieties and breeds.
d) An assessment of possible losses of biodiversity associated with reduction in the use of
these breeds and varieties and the farming systems associated with them
Shift in the LHC Higgs diphoton mass peak from interference with background
The Higgs diphoton amplitude from gluon fusion at the LHC interferes with the
continuum background induced by quark loops. I investigate the effect of this
interference on the position of the diphoton invariant mass peak used to help
determine the Higgs mass. At leading order, the interference shifts the peak
towards lower mass by an amount of order 150 MeV or more, with the precise
value dependent on the methods used to analyze and fit the data.Comment: 10 pages. v2: comments on scale variation added, reference adde
Galaxy-Galaxy Lensing in the Hubble Deep Field: The Halo Tully-Fisher Relation at Intermediate Redshift
A tangential distortion of background source galaxies around foreground lens
galaxies in the Hubble Deep Field is detected at the 99.3% confidence level. An
important element of our analysis is the use of photometric redshifts to
determine distances of lens and source galaxies and rest-frame B-band
luminosities of the lens galaxies. The lens galaxy halos obey a Tully-Fisher
relation between halo circular velocity and luminosity; the typical lens
galaxy, at a redshift z = 0.6, has a circular velocity of 210 +/-40 km/s at M_B
= -18.5, if q_0 = 0.5. Control tests, in which lens and source positions and
source ellipticities are randomized, confirm the significance level of the
detection quoted above. Furthermore, a marginal signal is also detected from an
independent, fainter sample of source galaxies without photometric redshifts.
Potential systematic effects, such as contamination by aligned satellite
galaxies, the distortion of source shapes by the light of the foreground
galaxies, PSF anisotropies, and contributions from mass distributed on the
scale of galaxy groups are shown to be negligible. A comparison of our result
with the local Tully-Fisher relation indicates that intermediate-redshift
galaxies are fainter than local spirals by 1.0 +/- 0.6 B mag at a fixed
circular velocity. This is consistent with some spectroscopic studies of the
rotation curves of intermediate-redshift galaxies. This result suggests that
the strong increase in the global luminosity density with redshift is dominated
by evolution in the galaxy number density.Comment: Revised version with minor changes. 13 pages, 7 figures, LaTeX2e,
uses emulateapj and multicol styles (included). Accepted by Ap
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